,,the ,,story ,,of ,,the ,,living ,,machine ,a ,,review ,,of ,,the ,,conclusions ,,of ,,modern ,,biology ,,in ,,regard ,,to ,,the ,,mechanism ,,which ,,controls ,,the ,,phenomena ,,of ,,living ,,activity ,,by ,h4,w4 ,,conn ,,professor ,,of ,,biology ,,in ,,wesleyan ,,university ,,author ,,of ,,the ,,story ,,of ,,germ ,,life1 ,,evolution ,,of ,,to-,,day1 ,,the ,,living ,,world1 ,,etc4 ,,with ,,fifty ,,illustrations ,,new ,,york ,d4 ,,appleton ,,and ,,company #aijc ,,copyright1 #ahii1 ,by ,d4 ,,appleton ,,and ,,company4 ,,preface4 ,that the living body is a machine is a statement that is frequently made without any very accurate idea as to what it means4 ,on the one hand it is made with a belief that a strict comparison can be made between the body and an ordinary1 artificial machine1 and that living beings are thus reduced to simple mechanisms2 on the other hand it is made loosely1 without any special thought as to its significance1 and certainly with no conception that it reduces life to a mechanism4 ,the conclusion that the living body is a machine1 involving as it does a mechanical conception of life1 is one of most extreme philosophical importance1 and no one interested in the philosophical conception of nature can fail to have an interest in this problem of the strict accuracy of the statement that the body is a machine4 ,doubtless the complete story of the living machine can not yet be told2 but the studies of the last fifty years have brought us so far along the road toward its completion that a review of the progress made and a glance at the yet unexplored realms and unanswered questions will be profitable4 ,for this purpose this work is designed1 with the hope that it may give a clear idea of the trend of recent biological science and of the advances made toward the solution of the problem of life4 ,,middletown1 ,,conn41 ,u4,s4,a4 ,october #a1 #ahih4 ,,contents4 ,,page ,,introduction--,biology a new science--,historical biology--,conservation of energy--,evolution--,cytology--,new aspects of biology--,the mechanical nature of living organisms--,significance of the new biological problems--,outline of the subject #a ,,part ,i4 ,,the ,,running ,,of ,,the ,,living ,,machine4 ,,chapter ,i4 ,,is ,,the ,,body ,a ,,machine8 ,what is a machine8--,a general comparison of a body and a machine--,details of the action of the machine--,physical explanation of the chief vital functions--,the living body is a machine--,the living machine constructive as well as destructive--,the vital factor #ai ,,chapter ,,ii4 ,,the ,,cell ,,and ,,protoplasm4 ,vital properties--,the discovery of cells--,the cell doctrine--,the cell--,the cellular structure of organisms--,the cell wall--,protoplasm--,the reign of protoplasm--,the decline of the reign of protoplasm--,the structure of protoplasm--,the nucleus--,centrosome--,function of the nucleus--,cell division or karyokinesis--,fertilization of the egg--,the significance of fertilization--,what is protoplasm8--,reaction against the cell doctrine--,fundamental vital activities as located in cells--,summary #ed ,,part ,,ii4 ,,the ,,building ,,of ,,the ,,living ,,machine4 ,,chapter ,,iii4 ,,the ,,factors ,,concerned ,,in ,,the ,,building ,,of ,,the ,,living ,,machine4 ,history of the living machine--,evidence for this history--,historical--,embryological--,a natomical--,significance of these sources of history--,forces at work in the building of the living machine--,reproduction--,heredity--,vari ation--,inheritance of variations--,method of machine building--,migration and isolation--,direct influence of environment--,consciousness--,summary of ,nature's power of building machines--,the origin of the cell machine--,general summary #aca ,,list ,,of ,,illustrations4 ,,figure ,,page ,amoeba ,polypodia in six successive stages of division ,frontispiece #a4 ,figure illustrating osmosis #cj #b4 ,figure illustrating osmosis #ca #c4 ,diagram of the intestinal walls #cb #d4 ,diagram of a single villus #cc #e4 ,enlarged figure of four cells in the villus membrane #cc #f4 ,a bit of muscle showing blood-vessels #cf #g4 ,a bit of bark showing cellular structure #fa #h4 ,successive stages in the division of the developing egg #fc #i4 ,a typical cell #fe #aj4 ,cells at a root tip #ff #aa4 ,section of a leaf showing cells of different shapes #ff #ab4 ,plant cells with thick walls1 from a fern #fg #ac4 ,section of potato #fg #ad4 ,various shaped wood cells from plant tissue #fh #ae4 ,a bit of cartilage #fh #af4 ,frogs' blood #fi #ag4 ,a bit of bone #fi #ah4 ,connective tissue #gj #ai4 ,a piece of nerve fibre #gj #bj4 ,a muscle fibre #ga #ba4 ,a complex cell1 vorticella #ga #bb4 ,an amoeba #gc #bc4 ,a cell as it appears to the modern microscope #hf #bd4 ,a cell cut into pieces1 each containing a bit of nucleus #hi #be4 ,a cell cut in pieces1 only one of which contains any nucleus #ij #bf4 ,different forms of nucleii #ic #bg and #bh4 ,two stages in cell division #if #bi and #cj4 ,stages in cell division #ih #ca and #cb4 ,latest stages in cell division #ajj #cc4 ,an egg #ajc #cd and #ce4 ,stages in the process of fertilization of the egg #ajd #cf and #cg4 ,stages in the process of fertilization of the egg #aje #ch1 #ci1 and #dj4 ,stages in fertilization of the egg #ajf #da and #db4 ,latest stages in the fertilization of the egg #aji #dc and #dd4 ,two stages in the division of the egg #aaa #de4 ,a group of cells resulting from division1 the first step in machine building #ace #df4 ,a later step in machine building1 the gastrula #ace #dg4 ,the arm of a monkey #add #dh4 ,the arm of a bird #add #di4 ,the arm of an ancient half-bird1 half-reptile animal #add #ej4 ,diagram to illustrate the principle of heredity #aef ,,the ,,story ,,of ,,the ,,living ,,machine4 ,,introduction4 ,biology a ,new ,science4--,in recent years biology has been spoken of as a new science4 ,thirty years ago departments of biology were practically unknown in educational institutions4 ,to-day none of our higher institutions of learning considers itself equipped without such a department4 ,this seems to be somewhat strange4 ,biology is simply the study of living things2 and living nature has been studied as long as mankind has studied anything4 ,even ,aristotle1 four hundred years before ,christ1 classified living things4 ,from this foundation down through the centuries living phenomena have received constant attention4 ,recent centuries have paid more attention to living things than to any other objects in nature4 ,linnus erected his systems of classification before modern chemistry came into existence2 the systematic study of zoology antedated that of physics2 and long before geology had been conceived in its modern form1 the animal and vegetable kingdoms had been comprehended in a scientific system4 ,how1 then1 can biology be called a new science ,when it is older than all the others8 ,there must be some reason why this1 the oldest of all1 has been recently called a new science1 and some explanation of the fact that it has only recently advanced to form a distinct department in our educational system4 ,the reason is not difficult to find4 ,biology is a new science1 not because the objects it studies are new1 but because it has adopted a new relation to those objects and is studying them from a new standpoint4 ,animals and plants have been studied long enough1 but not as we now study them4 ,perhaps the new attitude adopted toward living nature may be tersely expressed by saying that in the past it has been studied as at rest1 while to-day it is studied as in motion4 ,the older zoologists and botanists confined themselves largely to the study of animals and plants simply as so many museum specimens to be arranged on shelves with appropriate names4 ,the modern biologist is studying these same objects as intensely active beings and as parts of an ever-changing history4 ,to the student of natural history fifty years ago1 animals and plants were objects to be classified2 to the biologist of to-day1 they are objects to be explained4 ,to understand this new attitude1 a brief review of the history of the fundamental features of philosophical thought will be necessary4 ,when1 long ago1 man began to think upon the phenomena of nature1 he was able to understand almost nothing4 ,in his inability to comprehend the activities going on around him he came to regard the forces of nature as manifestations of some supernatural beings4 ,this was eminently natural4 ,he had a direct consciousness of his own power to act1 and it was natural for him to assume that the activities going on around him were caused by similar powers on the part of some being like himself1 only superior to him4 ,thus he came to fill the unseen universe with gods controlling the forces of nature4 ,the wind was the breath of one god1 and the lightning a bolt thrown from the hands of another4 ,with advancing thought the ideas of polytheism later gave place to the nobler conception of monotheism4 ,but for a long time yet the same ideas of the supernatural1 as related to the natural1 retained their place in man's philosophy4 ,those phenomena which he thought he could understand were looked upon as natural1 while those which he could not understand were looked upon as supernatural1 and as produced by the direct personal activity of some divine agency4 ,as the centuries passed1 and man's power of observation became keener and his thinking more logical1 many of the hitherto mysterious phenomena became intelligible and subject to simple explanations4 ,as fast as this occurred these phenomena were unconsciously taken from the realm of the supernatural and placed among natural phenomena which could be explained by natural laws4 ,among the first mysteries to be thus comprehended by natural law were those of astronomy4 ,the complicated and yet harmonious motions of the heavenly bodies had hitherto been inexplicable4 ,to explain them many a sublime conception of almighty power had arisen1 and the study of the heavenly bodies ever gave rise to the highest thoughts of ,deity4 ,but ,newton's law of gravitation reduced the whole to the greatest simplicity4 ,through the law and force of gravitation these mysteries were brought within the grasp of human understanding4 ,they ceased to be looked upon as supernatural1 and became natural phenomena as soon as the force of gravitation was accepted as a part of nature4 ,in other branches of natural phenomena the same history followed4 ,the forces and laws of chemical affinity were formulated and studied1 and physical laws and forces were comprehended4 ,as these natural forces were grasped it became1 little by little1 evident that the various phenomena of nature were simply the result of nature's forces acting in accordance with nature's laws4 ,phenomena hitherto mysterious were one after another brought within the realm of law1 and as this occurred a smaller and smaller portion of them were left within the realm of the so-called supernatural4 ,by the middle of this century this advance had reached a point where scientists1 at least1 were ready to believe that nature's forces were all-powerful to account for nature's phenomena4 ,science had passed from the reign of mysticism to the reign of law4 ,but after chemistry and physics1 with all the forces that they could muster1 had exhausted their powers in explaining natural phenomena1 there apparently remained one class of facts which was still left in the realm of the supernatural and the unexplained4 ,the phenomena associated with living things remained nearly as mysterious as ever4 ,life appeared to be the most inexplicable phenomena of nature1 and none of the forces and laws which had been found sufficient to account for other departments of nature appeared to have much influence in rendering intelligible the phenomena of life4 ,living organisms appeared to be actuated by an entirely unique force4 ,their shapes and structure showed so many marvellous adaptations to their surroundings as to render it apparently certain that their adjustment must have been the result of some intelligent planning1 and not the outcome of blind force4 ,who could look upon the adaptation of the eye to light without seeing in ,it the result of intelligent design8 ,adaptation to conditions is seen in all animals and plants4 ,these organisms are evidently complicated machines with their parts intricately adapted to each other and to surrounding conditions4 ,apart from animals and plants the only other similarly adjusted machines are those which have been made by human intelligence2 and the inference seemed to be clear that a similar intelligence was needed to account for the living machine4 ,the blind action of physical forces seemed inadequate4 ,thus the phenomena of life1 which had been studied longer than any other phase of nature1 continued to stand aloof from the rest and refused to fall into line with the general drift of thought4 ,the living world seemed to give no promise of being included among natural phenomena1 but still persisted in retaining its supernatural aspect4 ,it is the attempt to explain the phenomena of the living world by the same kind of natural forces that have been adequate to account for other phenomena1 that has created modern ,biology4 ,so long as students simply studied animals and plants as objects for classification1 as museum objects1 or as objects which had been stationary in the history of nature1 so long were they simply following along the same lines in which their predecessors had been travelling4 ,but when once they began to ask if living nature were not perhaps subject to an intelligent explanation1 to study living things as part of a general history and to look upon them as active moving objects whose motion and whose history might perhaps be accounted for1 then at once was created a new department of thought and a new science inaugurated4 ,historical ,geology4--,preparation had been made for this new method of studying life by the formulation of a number of important scientific discoveries4 ,prominent among these stood historical geology4 ,that the earth had left a record of her history in the rocks in language plain enough to be read appears to have been impressed upon scientists in the last of the century4 ,that the earth has had a history and that man could read it became more and more thoroughly understood as the first decades of this century passed4 ,the reading of that history proved a somewhat difficult task4 ,it was written in a strange language1 and it required many years to discover the key to the record4 ,but under the influence of the writings of ,lyell1 just before the middle of the century1 it began to appear that the key to this language is to be found by simply opening the eyes and observing what is going on around us to-day4 ,a more extraordinary and more important discovery has hardly ever been made1 for it contained the foundation of nearly all scientific discoveries which have been made since4 ,this discovery proclaimed that an application of the forces still at work to-day on the earth's surface1 but continued throughout long ages1 will furnish the interpretation of the history written in the rocks1 and thus an explanation of the history of the earth itself4 ,the slow elevation of the earth's crust1 such as is still going on to-day1 would1 if continued1 produce mountains2 and the washing away of the land by rains and floods1 such as we see all around us1 would1 if continued through the long centuries1 produce the valleys and gorges which so astound us4 ,the explanation of the past is to be found in the present4 ,but this geological history told of a history of life as well as a history of rocks4 ,the history of the rocks has indeed been bound up in the history of life1 and no sooner did it appear that the earth's crust has had a readable history than it appeared that living nature had a parallel history4 ,if the present is a key to the past in interpreting geological history1 should not the same be true of this history of life8 ,it was inevitable that problems of life should come to the front1 and that the study of life from the dynamical standpoint1 rather than a statical1 should ensue4 ,modern biology was the child of historical geology4 ,but historical geology alone could never have led to the dynamical phase of modern biology4 ,three other conceptions have contributed in an even greater degree to the development of this science4 ,conservation of ,energy4--,the first of these was the doctrine of conservation of energy and the correlation of forces4 ,this doctrine is really quite simple1 and may be outlined as follows3 ,in the universe1 as we know it1 there exists a certain amount of energy or power of doing work4 ,this amount of energy can neither be increased nor decreased2 energy can no more be created or destroyed than matter4 ,it exists1 however1 in a variety of forms1 which may be either active or passive4 ,in the active state it takes some form of motion4 ,the various forces which we recognize in nature--heat1 light1 electricity1 chemism1 etc4--are simply forms of motion1 and thus forms of this energy4 ,these various types of energy1 being only expressions of the universal energy1 are convertible into each other in such a way that when one disappears another appears4 ,a cannon ball flying through the air exhibits energy of motion2 but it strikes an obstacle and stops4 ,the motion has apparently stopped1 but an examination shows that this is not the case4 ,the cannon ball and the object it strikes have been heated1 and thus the motion of the ball has simply been transformed into a different form of motion1 which we call heat4 ,or1 again1 the heat set free under the locomotive boiler is converted by machinery into the motion of the locomotive4 ,by still different mechanism it may be converted into electric force4 ,all forms of motion are readily convertible into each other1 and each form in which energy appears is only a phase of the total energy of nature4 ,a second condition of energy is energy at rest1 or potential energy4 ,a stone on the roof of a house is at rest1 but by virtue of its position it has a certain amount of potential energy1 since1 if dislodged1 it will fall to the ground1 and thus develop energy of motion4 ,moreover1 it required to raise the stone to the roof the expenditure of an amount of energy exactly equal to that which will reappear if the stone is allowed to fall to the ground4 ,so in a chemical molecule1 like fat1 there is a store of potential energy which may be made active by simply breaking the molecule to pieces and setting it free4 ,this occurs when the fat burns and the energy is liberated as heat4 ,but it required at some time the expenditure of an equal amount of energy to make the molecule4 ,when the molecule of fat was built in the plant which produced it1 there was used in its construction an amount of solar energy exactly equivalent to the energy which may be liberated by breaking the molecule to pieces4 ,the total sum of the active and potential energy in the universe is thus at all times the same4 ,this magnificent conception has become the cornerstone of modern science4 ,as soon as conceived it brought at once within its grasp all forms of energy in nature4 ,it is primarily a physical doctrine1 and has been developed chiefly in connection with the physical sciences4 ,but it shows at once a possible connection between living and non-living nature4 ,the living organism also exhibits motion and heat1 and1 if the doctrine of the conservation of energy be true1 this energy must be correlated with other forms of energy4 ,here is a suggestion that the same laws control the living and the non-living world2 and a suspicion that if we can find a natural explanation of the burning of a piece of coal and the motion of a locomotive1 so1 too1 we may find a natural explanation of the motion of a living machine4 ,evolution--,a second conception1 whose influence upon-the development of biology was even greater1 was the doctrine of evolution4 ,it is true that the doctrine of evolution was no new doctrine with the middle of this century1 for it had been conceived somewhat vaguely before4 ,but until historical geology had been formulated1 and until the idea of the unity of nature had dawned upon the minds of scientists1 the doctrine of evolution had little significance4 ,it made little difference in our philosophy whether the living organisms were regarded as independent creations or as descended from each other1 so long as they were looked upon as a distinct realm of nature without connection with the rest of nature's activity4 ,if they are distinct from the rest of nature1 and therefore require a distinct origin1 it makes little difference whether we looked upon that origin as a single originating point or as thousands of independent creations4 ,but so soon as it appeared that the present condition of the earth's crust was formed by the action of forces still in existence1 and so soon as it appeared that the forces outside of living forces1 including astronomical1 physical and chemical forces1 are all correlated with each other as parts of the same store of energy1 then the problem of the origin of living things assumed a new meaning4 ,living things became then a part of nature1 and demanded to be included in the same general category4 ,the reign of law1 which was claiming that all nature's phenomena are the result of natural rather than supernatural powers1 demanded some explanation of the origin of living things4 ,consequently1 when ,darwin pointed out a possible way in which living phenomena could thus be included in the realm of natural law1 science was ready and anxious to receive his explanation4 ,cytology4--,a third conception which contributed to the formulation of modern biology was derived from the facts discovered in connection with the organic cell and protoplasm4 ,the significance of these facts we shall notice later1 but here we may simply state that these discoveries offered to students simplicity in the place of complexity4 ,the doctrine of cells and protoplasm appeared to offer to biologists no longer the complicated problems which were associated with animals and plants1 but the same problems stripped of all side issues and reduced to their lowest terms4 ,this simplifying of the problems proved to be an extraordinary stimulus to the students who were trying to find some way of understanding life4 ,new ,aspects of ,biology4--,these three conceptions seized hold of the scientific world at periods not very distant from each other1 and their influence upon the study of living nature was immediate and extraordinary4 ,living things now came to be looked upon not simply as objects to be catalogued1 but as objects which had a history1 and a history which was of interest not merely in itself1 but as a part of a general plan4 ,they were no longer studied as stationary1 but as moving phases of nature4 ,animals were no longer looked upon simply as beings now existing1 but as the results of the action of past forces and as the foundation of a different series of beings in the future4 ,the present existing animals and plants came to be regarded simply as a step in the long history of the universe4 ,it appeared at once that the study of the present forms of life would offer us a means of interpreting the past and perhaps predicting the future4 ,in a short time the entire attitude which the student assumed toward living phenomena had changed4 ,biological science assumed new guises and adopted new methods4 ,even the problems which it tried to solve were radically changed4 ,hitherto the attempt had been made to find instances of purpose in nature4 ,the marvellous adaptations of living beings to their conditions had long been felt1 and the study of the purposes of these adaptations had inspired many a magnificent conception4 ,but now the scientist lost sight of the purpose in hunting for the cause4 ,natural law is blind and can have no purpose4 ,to the scientist1 filled with the thought of the reign of law1 purpose could not exist in nature4 ,only cause and effect appeal to him4 ,the present phenomena are the result of forces acting in the past1 and the scientist's search should be not for the purpose of an adaptation1 but for the action of the forces which produced it4 ,to discover the forces and laws which led to the development of the present forms of animals and plants1 to explain the method by which these forces of nature have acted to bring about present results1 these became the objects of scientific research4 ,it no longer had any meaning to find that a special organ was adapted to its conditions2 but it was necessary to find out how it became adapted4 ,the difference in the attitude of these two points of view is world-wide4 ,the former fixes the attention upon the end1 the latter upon the means by which the end was attained2 the former is what we sometimes call teleological1 the latter scientific2 the former was the attitude of the study of animals and plants before the middle of this century1 the latter the spirit which actuates modern biology4 ,the ,mechanical ,nature of ,living ,organisms4--,this new attitude forced many new problems to the front4 ,foremost among them and fundamental to them all were the questions as to the mechanical nature of living organisms4 ,the law of the correlation of force told that the various forms of energy which appear around us--light1 heat1 electricity1 etc4--are all parts of one common store of energy and convertible into each other4 ,the question whether vital energy is in like manner correlated with other forms of energy was now extremely significant4 ,living forces had been considered as standing apart from the rest of nature4 ,vital force1 or vitality1 had been thought of as something distinct in itself2 and that there was any measurable relation between the powers of the living organism and the forces of heat and chemical affinity was of course unthinkable before the formulation of the doctrine of the correlation of forces4 ,but as soon as that doctrine was understood it began to appear at once that1 to a certain extent at least1 the living body might be compared to a machine whose function is simply to convert one kind of energy into another4 ,a steam engine is fed with fuel4 ,in that fuel is a store of energy deposited there perhaps centuries ago4 ,the rays of the sun1 shining on the world in earlier ages1 were seized upon by the growing plants and stored away in a potential form in the wood which later became coal4 ,this coal is placed in the furnace of the steam engine and is broken to pieces so that it can no longer hold its store of energy1 which is at once liberated in its active form as heat4 ,the engine then takes the energy thus liberated1 and as a result of its peculiar mechanism converts it into the motion of its great fly-wheel4 ,with this notion clearly in mind the question forces itself to the front whether the same facts are not true of the living animal organism4 ,it1 too1 is fed with food containing a store of energy2 and should we not regard it1 like the steam engine1 simply a machine for converting this potential energy into motion1 heat1 or some other active form8 ,this problem of the correlation of vital and physical forces is inevitably forced upon us with the doctrine of the correlation of forces4 ,plainly1 however1 such questions were inconceivable before about the middle of the nineteenth century4 ,this mechanical conception of living activity was carried even farther4 ,under the lead of ,huxley there arose in the seventh decade of the century a view of life which reduced it to a pure mechanism4 ,the microscope had1 at that time1 just disclosed the universal presence in living things of that wonderful substance1 protoplasm4 ,this material appeared to be a homogeneous substance1 and a chemical study showed it to be made of chemical elements united in such a way as to show close relation to albumens4 ,it appeared to be somewhat more complex than ordinary albumen1 but it was looked upon as a definite chemical compound1 or1 perhaps1 as a simple mixture of compounds4 ,chemists had shown that the properties of compounds vary with their composition1 and that the more complex the compound the more varied its properties4 ,it was a natural conception1 therefore1 that protoplasm was a complex chemical compound1 and that its vital properties were simply the chemical properties resulting from its composition4 ,just as water possesses the power of becoming solid at certain temperatures1 so protoplasm possesses the power of assimilating food and growing2 and1 since we do not doubt that the properties of water are the result of its chemical composition1 so we may also assume that the vital properties of protoplasm are the result of its chemical composition4 ,it followed from this conclusion that if chemists ever succeeded in manufacturing the chemical compound1 protoplasm1 it would be alive4 ,vital phenomena were thus reduced to chemical and mechanical problems4 ,these ideas arose shortly after the middle of the century1 and have dominated the development of biological science up to the present time4 ,it is evident that the aim of biological study must be to test these conceptions and carry them out into details4 ,the chemical and mechanical laws of nature must be applied to vital phenomena in order to see whether they can furnish a satisfactory explanation of life4 ,are the laws and forces of chemistry sufficient to explain digestion8 ,are the laws of electricity applicable to an understanding of nervous phenomena8 ,are physical and chemical forces together sufficient to explain life8 ,can the animal body be properly regarded as a machine controlled by mechanical laws8 ,or1 on the other hand1 are there some phases of life which the forces of chemistry and physics cannot account for8 ,are there limits to the application of natural law to explain life8 ,can there be found something connected with living beings which is force but not correlated with the ordinary forms of energy8 ,is there such a thing as vital energy1 or is the so-called vital force simply a name which we have given to the peculiar manifestations of ordinary energy as shown in the substance protoplasm8 ,these are some of the questions that modern biology is trying to answer1 and it is the existence of such questions which has made modern biology a new science4 ,such questions not only did not1 but could not1 have arisen before the doctrines of the conservation of energy and evolution had made their impression upon the thought of the world4 ,significance of the ,new ,biological ,problems--,it is further evident that the answers to these questions will have a significance reaching beyond the domain of biology proper and affecting the fundamental philosophy of nature4 ,the answer will determine whether or not we can accept in entirety the doctrines of the conservation of energy and evolution4 ,plainly if it should be found that the energy of animate nature was not correlated with other forms of energy1 this would demand either a rejection or a complete modification of our doctrine of the conservation of energy4 ,if an animal can create any energy within itself1 or can destroy any energy1 we can no longer regard the amount of energy of the universe as constant4 ,even if that subtile form of force which we call nervous energy should prove to be uncorrelated with other forms of energy1 the idea of the conservation of energy must be changed4 ,it is even possible that we must insist that the still more subtile form of force1 mental force1 must be brought within the scope of this great law in order that it be implicitly accepted4 ,this law has proved itself strictly applicable to the inanimate world1 and has then thrust upon us the various questions in regard to vital force1 and we must recognize that the real significance of this great law must rest upon the possibility of its application to vital phenomena4 ,no less intimate is the relation of these problems to the doctrine of evolution4 ,evolution tries to account for each moment in the history of the world as the result of the conditions of the moment before4 ,such a theory loses its meaning unless it can be shown that natural forces are sufficient to account for living phenomena4 ,if the supernatural must be brought in here and there to account for living phenomena1 then evolution ceases to have much meaning4 ,it is undoubtedly a fact that the rapidly developing ideas along the above mentioned lines of dynamical biology have1 been potent factors in bringing about the adoption of evolution4 ,certain it is that1 had it been found that no correlation could be traced between vital and non-vital forces1 the doctrine of evolution could not have stood1 and even now the special significance which we shall in the end give to evolution will depend upon how we succeed in answering the questions above outlined4 ,the fact is that this problem of the mechanical explanation of vital phenomena forms the capstone of the arch1 the sides of which are built of the doctrines of the conservation of energy and the theory of evolution4 ,to the presentation of these problems the following pages will be devoted4 ,the fact that both the doctrine of the conservation of energy and that of evolution are practically everywhere accepted indicates that the mechanical nature of vital forces is regarded as proved4 ,but there are still many questions which are not so easily answered4 ,it will be our purpose in the following discussion to ascertain just what are these problems in dynamical biology and how far they have been answered4 ,our object will be then in brief to discover to what extent the conception of the living organism as a machine is borne out by the facts which have been collected in the last quarter century1 and to learn where1 if anywhere1 limits have been found to our possibility of applying the forces of chemistry and physics to an explanation of life4 ,in other words1 we shall try to see how far we have been able to understand living phenomena in terms of natural force4 ,outline of the ,subject4--,the subject1 as thus presented1 resolves itself at once into two parts4 ,that the living organism is a machine is everywhere recognized1 although some may still doubt as to the completeness of the comparison4 ,in the attempt to explain the phenomena of life we have two entirely different problems4 ,the first is manifestly to account for the existence of this machine1 for such a completed piece of mechanism as a man or a tree cannot be explained as a result of simple accident1 as the existence of a rough piece of rock might be explained4 ,its intricacy of parts and their purposeful interrelation demands explanation1 and therefore the fundamental problem is to explain how this machine came into existence4 ,the second problem is simpler1 for it is simply to explain the running of the machine after it is made4 ,if the organism is really a machine1 we ought to be able to find some way of explaining its actions as we can those of a steam engine4 ,of these two problems the first is the more fundamental1 for if we fail to find an explanation for the existence of the machine1 our explanation of its method of action is only partly satisfactory4 ,but the second question is the simpler1 and must be answered first4 ,we cannot hope to explain the more puzzling matter of the origin of the machine unless we can first understand how it acts4 ,in our treatment of the subject1 therefore1 we shall divide it into two parts3 ,i4 ,the ,running of the ,living ,machine4 ,,ii4 ,the ,origin of the ,living ,machine4 ,,part ,i4 ,,the ,,running ,,of ,,the ,,living ,,machine4 99 99 99 99 99 ,,chapter ,i4 ,,is ,,the ,,body ,a ,,machine8 ,the problem before us in this section is to find out to what extent animals and plants are machines4 ,we wish to determine whether the laws and forces which regulate their activities are the same as the laws and forces with which we experiment in the chemical and physical laboratory1 and whether the principles of mechanics and the doctrine of the conservation of energy apply equally well in the living machine and the steam engine4 ,it might be inferred that the proper method of study would be to confine our attention largely to the simplest forms of life1 since the problems would be here less complicated1 and therefore of easier solution4 ,this1 however1 has not been nor can it be the method of study4 ,our knowledge of the processes of life have been derived largely from the most rather than the least complex forms4 ,we have a better knowledge of the physiology of man and his allies than any other animals4 ,the reason for this is plain enough4 ,in the first place1 there is a value in the knowledge of the life activities of man entirely apart from any theoretical aspects1 and hence human physiology has demanded attention for its own sake4 ,the practical utility of human physiology has stimulated its study for centuries2 and in the last fifty years of scientific progress it has been human physiology and that of allied animals that has attracted the chief attention of physiologists4 ,the result is that while the physiology of man is tolerably well known1 that of other animals is less understood the farther we get away from man and his allies4 ,for this reason most of our knowledge of the living body as a machine must be derived from the study of man4 ,this is1 however1 fortunate rather than otherwise4 ,in the first place1 it enables us to proceed from the known to the unknown2 and in the second place1 more interest attaches to the problem as connected with human physiology than along any other line4 ,in our discussion1 therefore1 we shall refer chiefly to the physiology of man4 ,if we find that the functions of human life are amenable to a mechanical explanation we cannot hesitate to believe that this will be equally true of the lower orders of nature4 ,for similar reasons little reference will be made to the mechanism of plant life4 ,the structure of the plant is simpler and its activities are much more easily referable to mechanical principles than are those of animals4 ,for these reasons it will only be necessary for us to turn our attention to the life activities of the higher animals4 ,what is a ,machine8--,turning now to our more immediate subject of the accuracy of the statement that the body is a machine1 we must first ask what is meant by a machine8 ,a brief definition of a machine might be as follows3 ,a machine is a piece of apparatus so designed that it can change one kind of energy into another for a definite purpose4 ,energy1 as already noticed1 is the power of doing work1 and its ordinary active forms are heat1 motion1 electricity1 light1 etc42 but it may be in a passive or potential form1 and in this form stored within a chemical molecule4 ,these various forms of energy are readily convertible into each other2 and any form of apparatus designed for the purpose of producing such a conversion is called a machine4 ,a dynamo is thus a machine so adjusted that when mechanical motion is supplied to it the energy of motion is converted into electricity2 while an electromotor1 on the other hand1 is a piece of apparatus so designed that when electricity is applied to it1 it is converted into motion4 ,a steam engine1 again1 is designed to convert potential or passive energy into active energy4 ,potential energy in the form of chemical composition 7coal7 is supplied to the engine1 and this energy is first liberated in the active form of heat and then is converted into the motion of the great fly-wheel4 ,in all these cases there is no energy or power created1 for the machine must be always supplied with an amount of energy equal to that which it gives back in another form4 ,indeed1 a larger amount of energy must be furnished the machine than is expected back1 for there is always an actual loss of available energy4 ,in the process of the conversion of one form of energy into another some of the energy1 from friction or other cause1 takes the form of heat1 and is then radiated into space beyond our reach4 ,it is1 of course1 not destroyed1 for energy cannot be destroyed2 but it has assumed a form called radiant heat1 which is not available for our uses4 ,a machine thus neither creates nor destroys energy4 ,it receives it in one form and gives it back in another form1 with an inevitable loss of a portion of the energy as radiant heat4 ,with this understanding1 we may now ask if the living body can be properly compared with a machine4 ,a ,general ,comparison of a ,body and a ,machine4--,that the living body exhibits the ordinary types of energy is of course clear enough when we remember that it is always in motion and is always radiating heat--two of the most common types of physical energy4 ,that this energy is supplied to the body as it is to other machines1 in the form of the energy of chemical composition1 will also need no further proof when it is remembered that it is necessary to supply the body with appropriate food in order that it may do work4 ,the food we eat1 like coal1 represents so much solar energy which is stored up by the agency of plant life1 and the close comparison between feeding the body to enable it to work and feeding the engine to enable it to develop energy is so evident that it demands no further demonstration4 ,the details of the problem may1 however1 present some difficulties4 ,the first question which presents itself is whether the only power the body possesses is1 as in the case with other machines1 to transform energy without being able to create or destroy it8 ,can every bit of energy shown by the living organism be accounted for by energy furnished in the food1 and conversely can all the energy furnished in the food be found manifested in the living organism8 ,the theoretical answer to this question in terms of the law of the conservation of energy is clear enough1 but it is by no means so easy to answer it by experimental data4 ,to obtain experimental demonstration it would be necessary to make an accurate determination of the amount of energy an individual receives during a given period1 and at the same time a similar measurement of the amount of energy liberated in his body either as motion or heat4 ,if the body is a machine1 these two should exactly balance1 and if they do not balance it would indicate that the living organism either creates or destroys energy1 and is therefore not a machine4 ,such experiments are exceedingly difficult4 ,they must be performed usually upon man rather than other animals1 and it is necessary to inclose an individual in an absolutely sealed space with arrangements for furnishing him with air and food in measured quantity1 and with appliances for measuring accurately the work he does and the heat given off from his body4 ,in addition1 it is necessary to measure the exact amount of material he eliminates in the form of carbonic acid and other excretions4 ,such experiments present many difficulties which have not yet been thoroughly overcome1 but they have been attempted by several investigators4 ,for the purpose of such an experiment scientists have allowed themselves to be shut up in a small chamber six or eight feet in length1 in which their only communication with the outer world is by telephone and through a small opening in the side of the chamber1 occasionally opened for a second or two to supply the prisoner with food4 ,in such a chamber they have remained as long as twelve days4 ,in these experiments it is necessary to take account not only of the food eaten1 but of the actual amount of this food which is used by the body4 ,if the person gains in weight1 this must mean that he is storing up in his body material for future use2 while if he loses in weight1 this means that he is consuming his own tissues for fuel4 ,careful daily records of his weight must therefore be taken4 ,estimates of the solids1 liquids1 and gases given off from his body must be obtained1 for to carry out the experiment an exact balance must be made between the income and the outgo4 ,the apparatus devised for such experiments has been made very delicate2 so delicate1 indeed1 that the rising of the individual in the box from his chair is immediately seen in a rise in temperature of the apparatus4 ,but even with this delicacy the apparatus is comparatively coarse1 and can measure only the most apparent forms of energy4 ,the more subtle types of energy1 such as nervous force1 if this is to be regarded as energy1 do not make any impression on the apparatus4 ,the obstacles in the way of these experiments do not particularly concern us1 but the general results are of the greatest significance for our purpose4 ,while1 for manifest reasons1 it has not been possible to carry on these experiments for any great length of time1 and while the results have not yet been very accurately refined1 they are all of one kind and teach unhesitatingly one conclusion4 ,so far as concerns measurable energy or measurable material1 the body behaves just like any other machine4 ,if the body is to do work in this respiration apparatus1 it does so only by breaking to pieces a certain amount of food and using the energy thus liberated1 and the amount of food needed is proportional to the amount of work done4 ,when the individual simply walks across the floor1 or even rises from his chair1 this is accompanied by an increase in the amount of food material broken up and a consequent increase in the amount of refuse matter eliminated and the heat given off4 ,the income and outgo of the body in both matter and energy is balanced4 ,if1 during the experimental period1 it is found that less energy is liberated than that contained in the food assimilated1 it is also found that the body has gained in weight1 which simply means that the extra energy has been stored in the body for future use4 ,no more energy can be obtained from the body than is furnished1 and for all furnished in the food an equivalent amount is regained4 ,there is no trace of any creation or destruction of energy4 ,while1 on account of the complexity of the experimenting1 an absolutely strict balance sheet cannot be made1 all the results are of the same nature4 ,so far as concerns measurable energy1 all the facts collected bear out the theoretical conception that the living body is to be regarded as a machine which converts the potential energy of chemical composition1 stored passively in its food1 into active energy of motion and heat4 ,it is found1 however1 that the body is a machine of a somewhat superior grade1 since it is able to convert this potential energy into motion with less loss than the ordinary machine4 ,as noticed above1 in all machines a portion of the energy is converted into heat and rendered unavailable by radiating into space4 ,in an ordinary engine only about one-fifteenth of the energy furnished in the coal can be regained in the form of motive power1 the rest being radiated from the machine as heat4 ,some of our better engines to-day utilize a somewhat larger part1 but most of them utilize less than one-tenth4 ,the experiments with the living body in the respiration apparatus above described1 give a means of determining the proportion of the energy furnished in the form of food which can be utilized in the form of motive force4 ,this figure appears to be decidedly larger than that obtained by any machine yet devised by man4 ,the conclusion of the matter up to this point is then clear4 ,if we leave out of account the phenomena of the nervous system1 which we shall consider presently1 the general income and outgo of the body as concerns matter and energy is such that the body must be regarded as a machine1 which1 like other machines1 simply transforms energy without creating or destroying it4 ,to this extent1 at least1 animals conform to the law of the conservation of energy and are veritable machines4 ,details of the ,action of the ,machine4--,we turn next to some of the subordinate problems concerning the details of the action of the living machine4 ,we have a clear understanding of the method of action of a steam engine4 ,its mechanism is simple1 and1 moreover1 it was designed by human intelligence4 ,we can understand how the force of chemical affinity breaks up the chemical composition of the coal1 how the heat thus liberated is applied to the water to vapourize it2 how the vapour is collected in the boiler under pressure2 how this pressure is applied to the piston in the cylinder1 and how this finally results in the revolution of the fly-wheel4 ,it is true that we do not understand the underlying forces of chemism1 etc41 but these forces certainly exist and are the foundation of science4 ,but the mechanism of the engine is intelligible4 ,our understanding of it is such that1 with the forces of chemistry and physics as a foundation1 we can readily explain the running of the machine4 ,our next problem1 therefore1 is to see if we can in the same way reach an understanding of the phenomena of the living machine4 ,can we1 by the use of these same chemical and physical forces1 explain the activities taking place in the living organism8 ,can the motion of the body1 for example1 be made as intelligible as the motion of the steam engine8 ,physical ,explanation of the ,chief ,vital ,functions4--,the living machine is1 of course1 vastly more complicated than the steam engine1 and there are many different processes which must be considered separately4 ,there is not space in a work of this size to consider them all carefully1 but we may select a few of the vital functions as illustrations of the method which is pursued4 ,it will be assumed that the fundamental processes of human physiology are understood by the reader1 and we shall try to interpret some of them in terms of chemical and physical force4 ,digestion4--,the first step in this transformation of fuel is the process of digestion4 ,now this process of digestion is nothing mysterious1 nor does it involve any peculiar or special forces4 ,digestion of food is simply a chemical change therein4 ,the food which is taken into the body in the form of sugar1 starch1 fat or protein1 is acted upon by the digestive juices in such a way that its chemical nature is slightly changed4 ,but the changes that thus occur are not peculiar to the living body1 since they will take place equally well in the chemist's laboratory4 ,they are simply changes in the molecular structure of the food material1 and only such changes as are simple and familiar to the chemist4 ,the forces which effect the change are undoubtedly those of chemical affinity4 ,the only feature of the process which is not perfectly intelligible in terms of chemical law is the nature of the digestive juices4 ,the digestive fluids of the mouth and stomach contain certain substances which possess a somewhat remarkable power1 inasmuch as they are able to bring about the chemical changes which occur in the digestion of food4 ,an example will make this clearer4 ,one of the digestive processes is the conversion of starch into sugar4 ,the relation of these two bodies is a very simple one1 starch being readily converted into sugar by the addition to its molecule of a molecule of water4 ,the change can not be produced by simply adding starch to water1 but the water must be introduced into the starch molecule4 ,this change can be brought about in a variety of ways1 and is undoubtedly effected by the forces of chemical affinity4 ,chemists have found simple methods of producing this chemical union1 and the manufacture of sugar out of starchy material has even become something of a commercial industry4 ,one of the methods by which this change can be produced is by adding to the starch1 along with some water1 a little saliva4 ,the saliva has the power of causing the chemical change to occur at once1 and the molecule of water enters into the starch molecule and forms sugar4 ,now we do not understand how this saliva possesses this power to induce the chemical change4 ,but apparently the process is of the simplest character and involves no greater mystery than chemical affinity4 ,we know that the saliva contains a certain material called a ferment1 which is the active agent in bringing about the change4 ,this ferment is not alive1 nor does it need any living environment for its action4 ,it can be separated from the saliva in the form of a dry amorphous powder1 and in this form can be preserved almost indefinitely1 retaining its power to effect the change whenever put under proper conditions4 ,the change of starch into sugar is thus a simple chemical change occurring under the influence of chemical affinity under certain conditions4 ,one of the conditions is the presence of this saliva ferment4 ,if we can not exactly understand how the ferment produces this action1 neither do we exactly understand how a spark causes a bit of gunpowder to explode4 ,but we can not doubt that the latter is a purely natural result of the relation of chemical and physical forces1 and there is no more reason for doubting it in the former case4 ,what is true of the digestion of starch by saliva is equally true of the digestion of other foods in the stomach and intestine4 ,each of the digestive juices contains a ferment which brings about a chemical change in the food4 ,the changes are always chemical changes and are the result of chemical forces4 ,apart from the presence of these ferments there is really little difference between laboratory chemistry and living chemistry4 ,absorption of food4--,the next function of this machine to attract our attention is the absorption of food from the intestine into the blood4 ,the digested food is carried down the alimentary canal in a purely mechanical fashion by muscular action1 and when it reaches the intestine it begins to pass through its walls into the blood4 ,in this absorption we find engaged another set of forces1 the chief of which appears to be the physical force of osmosis4 ,the force of osmosis has no special connection with life4 ,if a membrane separates two liquids of different composition 7,fig4 i71 a force is exerted on the liquids which cause them to pass through the membrane1 each passing through the membrane into the other compartment4 ,the force which drives these liquids through the membrane is considerable1 and may sometimes be exerted against considerable pressure4 ,a simple experiment will illustrate this force4 ,in ,fig4 #b is represented a membranous bag tightly fastened to a glass tube4 ,the bag is filled with a strong solution of sugar1 and is immersed in a vessel containing pure water4 ,under these conditions some of the sugar solution passes through the bag into the water1 and some of the water passes from the vessel into the bag4 ,but if the solution of sugar is inside the bag and the pure water outside1 the amount of liquid passing into the bag is greater than the amount passing out2 the bag soon becomes distended and the water even rises in the tube to a considerable height at a7,fig4 #b74 ,the force here concerned is a force known as osmosis or dialysis1 and is always exerted when two different solutions of certain substances are separated from each other by a membrane4 ,the substances in solution will1 under these conditions1 pass from the dense to the weaker solution4 ,the process is a purely physical one4 ,illustration3 ,,fig4 #a4--,to illustrate osmosis4 ,in the vessel ,a is a solution of sugar2 in ,b1 is pure water4 ,the two are separated by the membrane ,c4 ,the sugar passes through the membrane into ,b4 ,illustration3 ,,fig4 #b4--;,in the bladder ,a is a sugar solution4 ,in the vessel ,b is pure water4 ,sugar passes out and water into the bladder until it rises in the tube to a4 ,this process of osmosis lies at the basis of the absorption of food from the alimentary canal4 ,in the first place1 most of the food when swallowed is not soluble1 and therefore not capable of osmosis4 ,but the process of digestion1 as we have seen1 changes the chemical nature of the food4 ,the food1 as the result of chemical change1 has become soluble1 and after being dissolved it is dialyzable--i4e41 capable of osmosis4 ,after digestion1 therefore1 the food is dissolved in the liquids in the stomach and intestine1 and is in proper condition for dialysis4 ,furthermore1 the structure of the intestine is such as to produce conditions adapted for dialysis4 ,this can be understood from ,fig4 #c1 which represents diagrammatically a cross section through the intestinal wall4 ,within the intestinal wall1 at ,a1 is the food mass in solution4 ,at ,b are shown little projections of the intestinal wall1 called villi extending into this food and covered by a membrane4 ,one of these villi is shown more highly magnified in ,fig4 #d1 in which ,b shows this membrane4 ,inside of these villi are blood-vessels1 ,c1 and it will be thus seen that the membrane1 ,b1 separates two liquids1 one containing the dissolved food outside the villus1 and the other containing blood inside the villus4 ,here are proper conditions for osmosis1 and this process of dialysis will take place whenever the intestinal contents holds more dialyzable material than the blood4 ,under these conditions1 which will always occur after food has been digested by the digestive juices1 the food will begin to pass through this membranous wall of the intestine into the blood under the influence of the physical force of osmosis4 ,thus the primary factor in food absorption is a physical one4 ,we must notice1 however1 that the physical force of osmosis is not the only factor concerned in absorption4 ,in the first place1 it is found that the food during its passage through the intestinal wall1 or shortly afterwards1 undergoes a further change1 so that by the time it has fairly reached the blood it has again changed its chemical nature4 ,these changes are1 however1 of a chemical nature1 and1 while we do not yet know very much about them1 they are of the same sort as those of digestion1 and involve probably nothing more than chemical processes4 ,illustration3 ,,fig4 #c--;,diagram of the intestinal walls4 ,a1 lumen of intestine filled with digested food4 ,b1 villi1 containing blood vessels4 ,c1 larger blood vessel1 which carries blood with absorbed food away from the intestine4 ,secondly1 we notice that there is one phase of absorption which is still obscure4 ,part of the food is composed of fat1 and this fat1 as the result of digestion1 is mechanically broken up into extremely minute droplets4 ,although these droplets are of microscopic size they are not actually in solution1 and therefore not subject to the force of osmosis which only affects solutions4 ,the osmotic force will not force fat drops through membranes1 and to explain their passage through the walls of the intestine requires something additional4 ,we are as yet1 however1 able to give only a partial explanation of this matter4 ,the inner wall of the intestine is not an inert1 lifeless membrane1 but is made of active bits of living matter4 ,these bits of living matter appear to seize hold of the droplets of oil by means of little processes which they thrust out1 and then pass them through their own bodies to excrete them on their inner surface into the blood vessels4 ,fig4 #e shows a few of these living bits of the membrane1 each containing several such fat droplets4 ,this fat absorption thus appears to be a vital process1 and not one simply controlled by physical forces like osmosis4 ,here our explanation runs against what we call vital power of the ultimate elements of the body4 ,the consideration of this vital feature we must1 of course1 investigate further2 but this will be done later4 ,at present our purpose is a general comparison of the body and a machine1 and we may for a little postpone the consideration of this vital phenomenon4 ,illustration3 ,,fig4 #d4--;,diagram of a single villus enlarged4 ,b represents the membranous surface covering the villus2 ,c1 the blood-vessels within the villus4 ,illustration3 ,,fig4 #e4--;,an enlarged figure of four cells of the membrane ,b in ,fig4 #d4 ,the free surface is at a2 f shows fat droplets in process of passage through the cells4 ,circulation4--,the next piece of mechanism for us to consider in this machine is the device for distributing this fuel to the various parts of the machine where it is to be used as a source of energy1 corresponding in a sense to the fireman of a locomotive4 ,this mechanism we call the circulatory system4 ,it consists of a series of tubes1 or blood vessels1 running to every part of the body and supplying every bit of tissue4 ,within the tubes is the blood1 which1 from its liquid nature1 is easily forced around the body through the tubes4 ,at the centre of the system is a pump which keeps the blood in motion4 ,the tubes form a closed system1 such that the pump1 or heart1 may suck the blood in from one side to force it out into the tubes on the other side2 and the blood1 after passing over the body in this closed set of tubes1 is finally brought back again to be forced once more over the same path4 ,as this blood is carried around the body it conveys from one part of the machine to another all material that needs distribution4 ,while in the intestine1 as already noticed 7,fig4 #c71 it receives the food1 and now this food is carried by the circulation to the muscles or the other organs that need it4 ,while in the lungs the blood receives oxygen1 and this oxygen is then carried to those parts of the body that need it4 ,the circulatory system is thus simply a medium by which each part of the machine may receive its proper share of the supplies needed for its action4 ,now in this circulation we have again to do with chemical and physical forces4 ,all of its general phenomena are based upon purely mechanical principles4 ,the action of the heart--leaving out of consideration for a moment its muscular power--is that of a simple pump4 ,it is provided with valves whose action is as simple and as easy to understand as those of any water pump4 ,by the action of these valves the blood is kept circulating in one direction4 ,the blood vessels are elastic1 and the study of the effect of a liquid pumped rhythmically into elastic tubes explains with simplicity the various phenomena associated with the circulation4 ,for example1 the rhythmically contracting heart forces a small quantity of blood into the arteries at short intervals4 ,these tubes are large near the heart1 but smaller at their ends1 where they flow into the veins1 so that the blood does not flow out into the veins so readily as it flows in from the heart4 ,the jet of blood that is sent in with every beat of the heart slightly stretches the artery1 and the tension thus produced causes the blood to continue to flow between the beats4 ,but the heart continues beating1 and there is an accumulation of the blood in the arteries until it exists under some pressure--a pressure sufficient to force it rapidly through the small ends of the arteries into the veins4 ,after passing into the veins the pressure is at once removed1 since the veins are larger than the arteries1 and there is no resistance to the flow of the blood4 ,hence the blood in the arteries is under pressure1 while there is little or no pressure in the veins4 ,into the details of this matter we need not go1 but this will be sufficient to indicate that the whole process is a mechanical one4 ,we must not fail to see1 however1 that in this problem of circulation there are two points at least where once more we meet with that class of phenomena which we still call vital4 ,the beating of the heart is the first of these1 for this is active muscular power4 ,the second is a contraction of the smaller blood-vessels which regulates the blood supply4 ,both of these phenomena are phases of muscular activity1 and will be included under the discussion of other similar phenomena later4 ,illustration3 ,,fig4 #f4--;,a bit of muscle with its blood-vessels3 a1 the muscle fibres2 b1 the minute blood-vessels4 ,the fibres and vessels are bathed in lymph 7not shown in the figure71 and food material passes through the walls of the blood-vessels into this lymph4 ,we next notice that not only is the distribution of the blood explained upon mechanical principles1 but the supplying of the active parts of the body with food is in the same way intelligible4 ,as we have seen1 the blood coming from the intestine contains the food material received from the digested food4 ,now when this blood in its circulation flows through the active tissues--for instance1 the muscles--it is again placed under conditions where osmosis is sure to occur4 ,in the muscles the thin-walled blood-vessels are surrounded and bathed by a liquid called lymph4 ,figure #f shows a bit of muscle tissue1 with its blood-vessels1 which are surrounded by lymph4 ,the lymph1 which is not shown1 fills all the space outside the blood-vessels1 thus bathing both muscles and blood-vessels4 ,here again we have a membrane 7i4e41 the wall of the blood-vessel7 separating two liquids1 and since the lymph is of a different composition from the blood1 dialysis between them is sure to occur1 and the materials which passed into the blood in the intestine through the influence of the osmotic force1 now pass out into the lymph under the influence of the same force4 ,the food is thus brought into the lymph2 and since the lymph lies in actual contact with the living muscle fibres1 these fibres are now able to take directly from the lymph the material needed for their use4 ,the power which enables the muscle fibre to take the material it needs1 discarding the rest1 is1 again1 one of the vital processes which we defer for a moment4 ,respiration4--,pursuing the same line of study1 we turn for a moment to the relation of the circulatory system to the function of supplying the body with oxygen gas4 ,oxygen is absolutely needed to carry on the functions of life2 for these1 like those of the engine1 are based upon the oxidation of the fuel4 ,the oxygen is derived from the air in the simplest manner4 ,during its circulation the blood is brought for a fraction of a second into practical contact with air4 ,this occurs in the lungs1 where there are great numbers of air cells1 in the walls of which the blood-vessels are distributed in great profusion4 ,while the blood is in these vessels it is not indeed in actual contact with the air1 but is separated from it by only a very thin membrane--so thin that it forms no hindrance to the interchange of gases4 ,these air-cells are kept filled with air by simple muscular action4 ,by the contraction of the muscles of the thorax the thoracic cavity is enlarged1 and as a result air is sucked in in exactly the same way that it is sucked into a pair of bellows when expanded4 ,then the contraction of another set of muscles decreases the size of the thoracic cavity1 and the air is squeezed out again4 ,the action is just as truly mechanical as is that of the blacksmith's bellows4 ,the relation of the air to the blood is just as simple4 ,in the blood there are various chemical ingredients1 among which is one known as hmoglobin4 ,it does not concern us at present to ask where this material comes from1 since this question is part of the broader question1 the origin of the machine1 to be discussed in the second part of this work4 ,the hmoglobin is a normal constituent of the blood1 and1 being red in colour1 gives the red colour to the blood4 ,this hmoglobin has peculiar relations to oxygen4 ,it can be separated from the blood and experimented upon by the chemist in his laboratory4 ,it is found that when hmoglobin is brought in contact with oxygen1 under sufficient pressure it will form a chemical union with it4 ,this chemical union is1 however1 what the chemist calls a loose combination1 since it is readily broken up4 ,if the oxygen is above a certain rather low pressure1 the union will take place2 while if the pressure be below this point the union is at once destroyed1 and the oxygen leaves the hmoglobin to become free4 ,all of this is a purely chemical matter1 and can be demonstrated at will in a test tube in the laboratory4 ,but this union and disassociation is just what occurs as the foundation of respiration4 ,the blood coming to the lungs contains hmoglobin1 and since the oxygen pressure in the air is quite high1 this hmoglobin unites at once with a quantity of oxygen while the blood is flowing through the air-vessels4 ,the blood is then carried off in the circulation to the active tissues like the muscles4 ,these tissues are constantly using oxygen to carry on their life processes1 and consequently at all times use up about all the oxygen within their reach4 ,the result is that in these tissues the oxygen pressure is very low1 and when the oxygen-laden hmoglobin reaches them the association of the hmoglobin with oxygen is at once broken up and the oxygen set free in the tissue4 ,it passes at once to the lymph1 from which the active tissues seize it for the purpose of carrying on the oxidizing processes of the body4 ,this whole matter of supplying the body with oxygen is thus fundamentally a chemical one1 controlled by chemical laws4 ,removal of ,waste4--,the next step in this life process is one of difficulty4 ,after the food and oxygen have reached the tissues it is seized by the living cell4 ,the food material is now oxidized by the oxygen and its latent energy is liberated1 and appears in the form of motion or heat or some other vital function4 ,herein is the really mysterious part of the life process2 but for the present we will overlook the mystery of this action1 and consider the results from a purely material standpoint4 ,in a steam engine the fundamental process by which the latent energy of the fuel is liberated is that of oxidation4 ,the oxygen of the air unites with the chemical elements of the fuel1 and breaks up that fuel into simple compounds--which may be chiefly considered as three--carbonic dioxide 7,,co#b71 water 7,h#b,o71 and ash4 ,the energy contained in the original compound can not be held by these simpler bodies1 and it therefore escapes as heat4 ,just the same process1 with of course difference in details1 is found in the living machine4 ,the food1 after reaching the living cell1 is united with the oxygen1 and1 so far as chemical results are concerned1 the process is much the same as if it occurred outside the body4 ,the food is broken into simpler compounds and the contained energy is liberated4 ,the energy is1 by the mechanism of the machine1 changed into motion or nervous impulse1 etc4 ,the food is broken into simple compounds1 which are chiefly carbonic dioxide1 water1 and ash2 the ash being1 however1 quite different from the ash obtained from burning coal4 ,now the engine must have its chimney to remove the gases and vapours 7the ,,co#b and ,h#b,o7 and its ashpit for the ashes4 ,in the same way the living machine has its excretory system for removing wastes4 ,in the removal of the carbonic acid and water we have to do once more with the respiratory system1 and the process is simply a repetition of the story of gas diffusion1 chemical union1 and osmosis4 ,it is sufficient here to say that the process is just as simple and as easily explained as those already described4 ,the elimination of these wastes is simply a problem of chemistry and mechanics4 ,in the removal of the ash1 however1 we have something more1 for here again we are brought up against the vital action of the cell4 ,this ash takes chiefly the form of a compound known as urea1 which finds its way into the general circulatory system4 ,from the blood it is finally removed by the kidneys4 ,in the kidneys are a large number of bits of living matter 7kidney cells71 which have the power of seizing hold of the urea as the blood is flowing over them1 and after thus taking it out of the blood they deposit it in a series of tubes which lead to the bladder and hence to the exterior4 ,the bringing of this ash to the kidney cell is a mechanical matter1 based simply upon the flow of the blood4 ,the seizing of the urea by the kidney cell is a vital phenomenon which we must waive for the moment4 ,up to this point in the analysis there has been no difficulty1 and no one can fail to agree with the conclusions4 ,the position we reach is as follows3 ,so far as relates to the general problems of energy in the universe the body is a machine4 ,it neither creates nor destroys energy1 but simply transforms one form into another4 ,in attempting to explain the action of the machine1 we find that for the functions thus far considered 7sometimes called the vegetative functions7 the laws of chemistry and physics furnish adequate explanation4 ,we must now look a little further1 and question some of the functions the mechanical nature of which is less obvious4 ,the whole operation thus far described is under the control of the nervous system1 which acts somewhat like the engineer of an engine4 ,can this phase of living activity be included within the conception of the body as a machine8 ,nervous ,system4--,when we come to try to apply mechanical principles to the nervous system1 we meet with what seems at first to be no thoroughfare4 ,while dealing with the grosser questions of chemical compounds1 heat1 and motion1 there is little difficulty in applying natural laws to the explanation of living phenomena4 ,but the problem with the nervous system is very different4 ,it is only to-day that we are finding that the problem is open to study1 to say nothing of solution4 ,it is true that mental and other nervous phenomena have been studied for a long time1 but this study has been simply the study of these phenomena by themselves without a thought of their correlation with other phenomena of nature4 ,it is a matter of quite recent conception that nervous phenomena have any direct relation to the other realms of nature4 ,our first question must be whether we can find any correlation between nervous energy and other types of energy4 ,for our purpose it will be convenient to distinguish between the phenomena of simple nervous transmission and the phenomena of mental activity4 ,the former are the simpler1 and offer the greatest hope of solution4 ,if we are to find any correlation between nervous energy and other physical energy1 we must do so by finding some way of measuring nervous energy and comparing it with the latter4 ,this has been very difficult1 for we have no way of measuring a nervous impulse directly4 ,in the larger experiments upon the income and outgo of the body1 in the respiration apparatus mentioned above1 nervous phenomena apparently leave no trace4 ,so far as experiments have gone as yet1 there is no evidence of an expenditure of extra physical energy when the nervous system is in action4 ,this is not surprising1 however1 for this apparatus is entirely too coarse to measure such delicate factors4 ,that there is a correlation between nervous energy and physical energy is1 however1 pretty definitely proved by experiments along different lines4 ,the first step in this direction was to find that a nervous stimulus can be measured at least indirectly4 ,when the nerve is stimulated there passes from one end to the other an impulse1 and the rapidity with which it travels can be accurately measured4 ,when such an impulse reaches the brain it may give rise to a conscious sensation1 and a somewhat definite estimation can be made of the amount of time required for this4 ,the periods are very short1 of course1 but they are not instantaneous4 ,the nervous impulse1 can be studied in still other ways4 ,we find that the impulse can be started by ordinary forms of energy4 ,a mechanical shock1 a chemical or an electrical shock will develop nervous energy4 ,now these are ordinary forms of physical energy1 and if1 when they are applied to a nerve1 they give rise to a nervous stimulus1 the inference is certainly a legitimate one that the nerve is simply a bit of machinery adapted to the conversion of certain kinds of physical energy into nervous energy4 ,if this is the case1 then it is necessary to regard nervous energy as correlated with other forms of energy4 ,other facts point in the same direction4 ,not only can the nervous stimulus be developed by an electric shock1 but the strength of the stimulus is within certain limits proportional to the strength of the shock which produces it4 ,again1 not only is it found that an electrical shock can develop a nervous stimulus1 but conversely a nervous stimulus develops electrical energy4 ,in ordinary nerves1 even when not active1 slight electric currents can be detected4 ,they are extremely slight1 and require the most delicate instruments for their detection4 ,now when a nerve is stimulated these currents are immediately affected in such a way that under proper conditions they are increased in intensity4 ,the increase is sufficient to make itself easily seen by the motion of a galvanometer4 ,the motion of the galvanometer under these conditions gives a ready means of studying the character of the nervous impulse4 ,by its use it can be determined that the nerve impulse travels along the nerve like a wave1 and we can approximately determine the length and shape of the wave and its relative height at various points4 ,now what is the significance of all these facts for our discussion8 ,together they point clearly to the conclusion that nervous energy is correlated with other forms of physical energy4 ,since the nervous stimulus is started by other forms of energy1 and since it can1 in turn1 modify ordinary forms of energy1 we can not avoid the conclusion that the nervous impulse is only a special form of energy developed within the nerve4 ,it is a form of wave motion peculiar to the nerve substance1 but correlated with and developed from other types of energy4 ,this1 of course1 makes the nerve simply a bit of machinery4 ,if this conclusion is true1 the development of a nerve impulse would mean that a certain portion of food is broken to pieces in the body to liberate energy1 and this should be accompanied by an elimination of carbonic dioxide and heat4 ,this is easily shown to be true of muscle action4 ,when we remove a muscle from the body it may remain capable of contracting for some time4 ,by studying it under these conditions we find that it gives rise to carbonic dioxide and other substances1 and liberates heat whenever it contracts4 ,as already noticed1 in the respiration experiments1 whenever the individual experimented upon makes any motions1 there is an accompanying elimination of waste products and a development of heat4 ,but this does not appear to be demonstrable for the actions of the nervous system4 ,although very careful experiments have been made1 it has as yet been found impossible to detect any rise in temperature when a nerve impulse is passing through a nerve1 nor is there any demonstrable excretion of waste products4 ,this would be a serious objection to the conception of the nerve as a machine were it not for the fact that the nerve is so small that the total sum of its nervous energy must be very slight4 ,the total energy of this minute machine is so slight that it can not be detected by our comparatively rough instruments of measurement4 ,in short1 all evidence goes to show that the nerve impulse is a form of motion1 and hence of energy1 correlated with other forms of physical energy4 ,the nerve is1 however1 a very delicate machine1 and its total amount of energy is very small4 ,a tiny watch is a more delicate machine than a water-wheel1 and its actions are more dependent upon the accuracy of its adjustment4 ,the water-wheel may be made very coarse and yet be perfectly efficacious1 while the watch must be fashioned with extreme delicacy4 ,yet the water-wheel transforms vastly more energy than the watch4 ,it may drive the many machines in a factory1 while the watch can do no more than move itself4 ,but who can doubt that the watch1 as well as the water-wheel1 is governed by the law of the correlation of forces8 ,so the nervous system of the living machine is delicately adjusted and easily put out of order1 and its action involves only a small amount of energy2 but it is just as truly subject to the law of the conservation of energy as is the more massive muscle4 ,sensations4--,pursuing this subject further1 we next notice that it is possible to trace a connection between physical energy and sensations4 ,sensations are excited by certain external forms of motion4 ,the living machine has1 for example1 one piece of apparatus capable of being affected by rapidly vibrating waves of air4 ,this bit of the machine we call the ear4 ,it is made of parts delicately adjusted1 so that vibrating waves of air set them in motion1 and their motion starts a nervous stimulus travelling along the auditory nerve4 ,as a result this apparatus will be set in motion1 and an impulse sent along the auditory nerve whenever that external type of motion which we call sound strikes the ear4 ,in other words1 the ear is a piece of apparatus for changing air vibrations into nervous stimulation1 and is therefore a machine4 ,apparently the material in the ear is like a bit of gunpowder1 capable of being exploded by certain kinds of external excitation2 but neither the gunpowder nor the material in the ear develops any energy other than that in it at the outset4 ,in the same way the optic nerve has1 at its end1 a bit of mechanism readily excited by light vibrations of the ether1 and hence the optic nerve will always be excited when ether vibrations chance to have an opportunity of setting the optic machinery in motion4 ,and so on with the other senses4 ,each sensory nerve has1 at its end1 a bit of machinery designed for the transformation of certain kinds of external energy into nervous energy1 just as a dynamo is a machine for transforming motion into electricity4 ,if the machine is broken1 the external force has no longer any power of acting upon it1 and the individual becomes deaf or blind4 ,mental ,phenomena4--,thus far in our analysis we need not hesitate in recognizing a correlation between physical and nervous energy4 ,even though nervous energy is very subtle and only affects our instruments of measurements under exceptional conditions1 the fact that nervous forces are excited by physical forces1 and are themselves directly measurable1 indicates that they are correlated with physical forces4 ,up to this point1 then1 we may confidently say that the nervous system is part of the machine4 ,but when we turn to the more obscure parts of the nervous phenomena1 those which we commonly call mental1 we find ourselves obliged to stop abruptly4 ,we may trace the external force to the sensory organ1 we may trace this force into a nervous stimulus1 and may follow this stimulus to the brain as a wave motion1 and therefore as a form of physical energy4 ,but there we must stop4 ,we have no idea of how the nervous impulse is converted into a sensation4 ,the mental side of the sensation appears to stand in a category by itself1 and we can not look upon it as a form of energy4 ,it is true that many brave attempts have been made to associate the two4 ,sensations can be measured as to intensity1 and the intensity of a sensation is to a certain extent dependent upon the intensity of the stimulus exciting it4 ,the mental sensation is undoubtedly excited by the physical wave of nervous impulse4 ,in the growth of the individual the development of its mental powers are found to be parallel to the development of its nerves and brain--a fact which1 of course1 proves that mental power is dependent upon brain structure4 ,further1 it is found that certain visible changes occur in certain parts of the brain--the brain cells--when they are excited into mental activity4 ,such series of facts point to an association between the mental side of sensations and physical structure of the machine4 ,but they do not prove any correlation between them4 ,the unlikeness of mental and physical phenomena is so absolute that we must hesitate about drawing any connection between them4 ,it is impossible to conceive the mental side of a sensation as a form of wave motion4 ,if1 further1 we take into consideration the other phenomena associated with the nervous system1 the more distinctly mental processes1 we have absolutely no data for any comparison4 ,we can not imagine thought measured by units1 and until we can conceive of such measurement we can get no meaning from any attempt to find a correlation between mental and physical phenomena4 ,it is true that certain psychologists have tried to build up a conception of the physical nature of mind2 but their attempts have chiefly resulted in building up a conception of the physical nature of the brain1 and then ignoring the radical chasm that exists between mind and matter4 ,the possibility of describing a complex brain as growing parallel to the growth of a complex mind has been regarded as equivalent to proving their identity4 ,all attempts in this direction thus far have simply ignored the fact that the stimulation of a nerve1 a purely physical process1 is not the same thing as a mental action4 ,what the future may disclose it is hazardous to say1 but at present the mental side of the living machine has not been included within the conception of the mechanical nature of the organism4 ,the ,living ,body is a ,machine4--,reviewing the subject up to this point1 what must be our verdict as to our ability to understand the running of the living machine8 ,in the first place1 we are justified in regarding the body as a machine1 since1 so far as concerns its relations to energy1 it is simply a piece of mechanism--complicated1 indeed1 beyond any other machine1 but still a machine for changing one kind of energy into another4 ,it receives the energy in the form of chemical composition and converts it into heat1 motion1 nervous wave motion1 etc4 ,all of this is sure enough4 ,whether other forms of nervous and mental activity can be placed under the same category1 or whether these must be regarded as belonging to a realm by themselves and outside of the scope of energy in the physical sense1 can not perhaps be yet definitely decided4 ,we can simply say that as yet no one has been able even to conceive how thought can be commensurate with physical energy4 ,the utter unlikeness of thought and wave motion of any kind leads us at present to feel that on the side of mentality the comparison of the body with a machine fails of being complete4 ,in regard to the second half of the question1 whether natural forces are adequate to explain the running of the machine1 we have again been able to reach a satisfactory positive answer4 ,digestion1 assimilation1 circulation1 respiration1 excretion1 the principal categories of physiological action1 and at least certain phases of the action of the nervous system are readily understood as controlled by the action of chemical and physical forces4 ,in the accomplishment of these actions there is no need for the supposition of any force other than those which are at our command in the scientific laboratory4 ,the ,living ,machine ,constructive as well as ,destructive4--,in one respect the living machine differs from all others4 ,the action of all other machines results in the destruction of organized material1 and thus in a degradation of matter4 ,for example1 a steam engine receives coal1 a substance of high chemical composition1 and breaks it into more simple compounds1 in this way liberating its stored energy4 ,now if we examine all forms of artificial machines1 we find in the same way that there is always a destruction of compounds of high chemical composition4 ,in such machines it is common to start with heat as a source of energy1 and this heat is always produced by the breaking of chemical compounds to pieces4 ,in all chemical processes going on in the chemist's laboratory there is similarly a destruction of organic compounds4 ,it is true that the chemist sometimes makes complex compounds out of simpler ones2 but in order to do this he is obliged to use heat to bring about the combination1 and this heat is obtained from the destruction of a much larger quantity of high compounds than he manufactures4 ,the total result is therefore destruction rather than manufacture of high compounds4 ,thus it is a fact1 that in all artificial machines and in all artificial chemical processes there is1 as a total result1 a degradation of matter toward the simpler from the more complex compounds4 ,as a result of the action of the living machine1 however1 we have the opposite process of construction going on4 ,all high chemical compounds are to be traced to living beings as their source4 ,when green plants grow in sunlight they take simple compounds and combine them together to form more complex ones in such a way that the total result is an increase of chemical compounds of high complexity4 ,in doing this they use the energy of sunlight1 which they then store away in the compounds formed4 ,they thus produce starches1 oils1 proteids1 woods1 etc41 and these stores of energy now may be used by artificial machines4 ,the living machine builds up1 other machines pull down4 ,the living machine stores sunlight in complex compounds1 other machines take it out and use it4 ,the living organism is therefore to be compared to a sun engine1 which obtains its energy directly from the sun1 rather than to the ordinary engine4 ,while this does not in the slightest militate against the idea of the living body as a machine1 it does indicate that it is a machine of quite a different character from any other1 and has powers possessed by no other machine4 ,living machines alone increase the amount of chemical compounds of high complexity4 ,we must notice1 however1 that this power of construction in distinction from destruction1 is possessed only by one special class of living machines4 ,green plants alone can thus increase the store of organic compounds in the world4 ,all colourless plants and all animals1 on the other hand1 live by destroying these compounds and using the energy thus liberated2 in this respect being more like ordinary artificial machines4 ,the animal does indeed perform certain constructive operations1 manufacturing complex material out of simpler bodies2 as1 for example1 making fats out of starches4 ,but in this operation it destroys a large amount of organic material to furnish the energy for the construction1 so that the total result is a degradation of chemical compounds rather than a construction4 ,constructive processes1 which increase the amount of high compounds in nature1 are confined to the living machine1 and indeed to one special form of it1 viz41 the green plant4 ,this constructive power radically separates the living from other machines2 for while constructive processes are possible to the chemist1 and while engines making use of sunlight are possible1 the living machine is the only machine that increases the amount of high chemical compounds in the world4 ,the ,vital ,factor4--,with all this explanation of life processes it can not fail to be apparent that we have not really reached the centre of the problem4 ,we have explained many secondary processes1 but the primary ones are still unsolved4 ,in studying digestion we reach an understanding of everything until we come to the active vital property of the gland-cells in secreting4 ,in studying absorption we understand the process until we come to what we have called the vital powers of the absorptive cells of the alimentary canal4 ,the circulation is intelligible until we come to the beating of the heart and the contraction of the muscles of the blood-vessels4 ,excretion is also partly explained1 but here again we finally must refer certain processes to the vital powers of active cells4 ,and thus wherever we probe the problem we find ourselves able to explain many secondary problems1 while the fundamental ones we still attribute to the vital properties of the active tissues4 ,why a muscle contracts or a gland secretes we have certainly not yet answered4 ,the relation of the actions to the general problems of correlation of force is simple enough4 ,that a muscle is a machine in the sense of our definition is beyond question4 ,but the problem of why a muscle acts is not answered by showing that it derives its energy from broken food material4 ,there are plainly still left for us a number of fundamental problems1 although the secondary ones are soluble4 ,what can we say in regard to these fundamental vital powers of the active tissues8 ,firstly1 we must notice that many of the processes which we now understand were formerly classed as vital1 and we only retain under this term those which are not yet explained4 ,this1 of course1 suggests to us that perhaps we may some day find an explanation for all the so-called vital powers by the application of simple physical forces4 ,is it a fact that the only significance to the term vital is that we have not yet been able to explain these processes to our entire satisfaction8 ,is the difference between what we have called the secondary processes and the primary ones only one of degree8 ,is there a probability that the actions which we now call vital will some day be as readily understood as those which have already been explained8 ,is there any method by which we can approach these fundamental problems of muscle action1 heart beat1 gland secretion1 etc48 ,evidently1 if this is to be done1 it must be by resolving the body into its simple units and studying these units4 ,our study thus far has been a study of the machinery of the body as a whole2 but we have found that the various parts of the machine are themselves active1 that apart from the action of the general machine as a whole1 the separate parts have vital powers4 ,we must1 therefore1 get rid of this complicated machinery1 which confuses the problem1 and see if we can find the fundamental units which show these properties1 unencumbered by the secondary machinery which has hitherto attracted our attention4 ,we must turn now to the problem connected with protoplasm and the living cell1 since here1 if anywhere1 can we find the life substance reduced to its lowest terms4 ,,chapter ,,ii4 ,,the ,,cell ,,and ,,protoplasm4 ,vital ,properties4--,we have seen that the general activities of the body are intelligible according to chemical and mechanical laws1 provided we can assume as their foundation the simple vital properties of living phenomena4 ,we must now approach closer to the centre of the problem1 and ask whether we can trace these fundamental properties to their source and find an explanation of them4 ,in the first place1 what are these properties8 ,the vital powers are varied1 and lie at the basis of every form of living activity4 ,when we free them from complications1 however1 they may all be reduced to four4 ,these are3 7#a7 ,irritability1 or the property possessed by living matter of reacting when stimulated4 7#b7 ,movement1 or the power of contracting when stimulated4 7#c7 ,metabolism1 or the power of absorbing extraneous food and producing in it certain chemical changes1 which either convert it into more living tissue or break it to pieces to liberate the inclosed energy4 7#d7 ,reproduction1 or the power of producing new individuals4 ,from these four simple vital activities all other vital actions follow2 and if we can find an explanation of these1 we have explained the living machine4 ,if we grant that certain parts of the body can assimilate food and multiply1 having the power of contraction when irritated1 we can readily explain the other functions of the living machine by the application of these properties to the complicated machinery of the body4 ,but these properties are fundamental1 and unless we can grasp them we have failed to reach the centre of the problem4 ,as we pass from the more to the less complicated animals we find a gradual simplification of the machinery until the machinery apparently disappears4 ,with this simplification of the machinery we find the animals provided with less varied powers and with less delicate adaptations to conditions4 ,but withal we find the fundamental powers of the living organisms the same4 ,for the performance of these fundamental activities there is apparently needed no machinery4 ,the simple types of living bodies are simple in number of parts1 but they possess essentially the same powers of assimilation and growth that characterize the higher forms4 ,it is evident that in our attempt to trace the vital properties to their source we may proceed in two ways4 ,we may either direct our attention to the simplest organisms where all secondary machinery is wanting1 or to the smallest parts into which the tissues of higher organisms can be resolved and yet retain their life properties4 ,in either way we may hope to find living phenomena in its simplest form independent of secondary machinery4 ,but the fact is1 when we turn our attention in these two directions1 we find the result is the same4 ,if we look for the lowest organisms we find them among forms that are made of a single cell1 and if we analyze the tissues of higher animals we find the ultimate parts to be cells4 ,thus1 in either direction1 the study of the cell is forced upon us4 ,before beginning the study of the cell it will be well for us to try to get a clear notion of the exact nature of the problems we are trying to solve4 ,we wish to explain the activities of life phenomena in such a way as to make them intelligible through the application of natural forces4 ,that these processes are fundamentally chemical ones is evident enough4 ,a chemical oxidation of food lies at the basis of all vital activity1 and it is thus through the action of chemical forces that the vital powers are furnished with their energy4 ,but the real problem is what it is in the living machine that controls these chemical processes4 ,fat and starch may be oxidized in a chemist's test tubes1 and will there liberate energy2 but they do not1 under these conditions1 manifest vital phenomena4 ,proteid may be brought in contact with oxygen without any oxidation occurring1 and even if it is oxidized no motion or assimilation or reproduction occurs under ordinary conditions4 ,these phenomena occur only when the oxidation takes place in the living machine4 ,our problem is then to determine1 if possible1 what it is in the living machine that regulates the oxidations and other changes in such a way as to produce from them vital activities4 ,why is it that the oxidation of starch in the living machine gives rise to motion1 growth1 and reproduction1 while if the oxidation occurs in the chemist's laboratory1 or even in a bit of dead protoplasm1 it simply gives rise to heat8 ,one of the primary questions to demand attention in this search is whether we are to find the explanation1 at the bottom1 a chemical or a mechanical one4 ,in the simplest form of life in which vital manifestations are found are we to attribute these properties simply to chemical forces of the living substance1 or must we here too attribute them to the action of a complicated machinery8 ,this question is more than a formal one4 ,that it is one of most profound significance will appear from the following considerations3 ,chemical affinity is a well recognized force4 ,under the action of this force chemical compounds are produced and different compounds formed under different conditions4 ,the properties of the different compounds differ with their composition1 and the more complex are the compounds the more varied their properties4 ,now it might be assumed as an hypothesis that there could be a chemical compound so complex as to possess1 among other properties1 that of causing the oxidation of food to occur in such a way as to produce assimilation and growth4 ,such a compound would1 of course1 be alive1 and it would be just as true that its power of assimilating food would be one of its physical properties as it is that freezing is a physical property of water4 ,if such an hypothesis should prove to be the true one1 then the problem of explaining life would be a chemical one1 for all vital properties would be reducible to the properties of a chemical compound4 ,it would then only be necessary to show how such a compound came into existence and we should have explained life4 ,nor would this be a hopeless task4 ,we are well acquainted with forces adequate to the formation of chemical compounds4 ,if the force of chemical affinity is adequate under certain conditions to form some compounds1 it is easy to conceive it as a possibility under other conditions to produce this chemical living substance4 ,our search would need then to be for a set of conditions under which our living compound could have been produced by the known forces of chemical affinity4 ,but suppose1 on the other hand1 that we find this simplest bit of living matter is not a chemical compound1 but is in itself a complicated machine4 ,suppose that1 after reducing this vital substance to its simplest type1 we find that the substance with which we are dealing not only has complex chemical structure1 but that it also possesses a large number of structural parts adapted to each other in such a way as to work together in the form of an intricate mechanism4 ,the whole problem would then be changed4 ,to explain such a machine we could no longer call upon chemical forces4 ,chemical affinity is adequate to the explanation of chemical compounds however complicated1 but it cannot offer any explanation for the adaptation of parts which make a machine4 ,the problem of the origin of the simplest form of life would then be no longer one of chemical but one of mechanical evolution4 ,it is plain then that the question of whether we can attribute the properties of the simplest type of life to chemical composition or to mechanical structure is more than a formal one4 ,the ,discovery of ,cells4--,it is difficult for us to-day to have any adequate idea of the wonderful flood of light that was thrown upon scientific and philosophical study by the discoveries which are grouped around the terms cells and protoplasm4 ,cells and protoplasm have become so thoroughly a part of modern biology that we can hardly picture to ourselves the vagueness of knowledge before these facts were recognized4 ,perhaps a somewhat crude comparison will illustrate the relation which the discovery of cells had to the study of life4 ,imagine for a moment1 some intelligent being located on the moon and trying to study the phenomena on the earth's surface4 ,suppose that he is provided with a telescope sufficiently powerful to disclose moderately large objects on the earth1 but not smaller ones4 ,he would see cities in various parts of the world with wide differences in appearance1 size1 and shape4 ,he would see railroad trains on the earth rushing to and fro4 ,he would see new cities arising and old ones increasing in size1 and we may imagine him speculating as to their method of origin and the reasons why they adopt this or that shape4 ,but in spite of his most acute observations and his most ingenious speculation1 he could never understand the real significance of the cities1 since he is not acquainted with the actual living unit4 ,imagine now1 if you will1 that this supramundane observer invents a telescope which enables him to perceive more minute objects and thus discovers human beings4 ,what a complete revolution this would make in his knowledge of mundane affairs6 ,we can imagine how rapidly discovery would follow discovery2 how it would be found that it was the human beings that build the houses1 construct and run the railroads1 and control the growth of the cities according to their fancy2 and1 lastly1 how it would be learned that it is the human being alone that grows and multiplies and that all else is the result of his activities4 ,such a supramundane observer would find himself entering into a new era1 in which all his previous knowledge would sink into oblivion4 ,something of this same sort of revolution was inaugurated in the study of living things by the discovery of cells and protoplasms4 ,animals and plants had been studied for centuries and many accurate and painstaking observations had been made upon them4 ,monumental masses of evidence had been collected bearing upon their shapes1 sizes1 distribution1 and relations4 ,anatomy had long occupied the attention of naturalists1 and the general structure of animals and plants was already well known4 ,but the discoveries starting in the fourth decade of the century by disclosing the unity of activity changed the aspect of biological science4 ,the ,cell ,doctrine4--,the cell doctrine is1 in brief1 the theory that the bodies of animals and plants are built up entirely of minute elementary units1 more or less independent of each other1 and all capable of growth and multiplication4 ,this doctrine is commonly regarded as being inaugurated in #ahci by ,schwann4 ,long before this1 however1 many microscopists had seen that the bodies of plants are made up of elementary units4 ,in describing the bark of a tree in #affe1 ,robert ,hooke had stated that it was composed of little boxes or cells1 and regarded it as a sort of honeycomb structure with its cells filled with air4 ,the term cell quite aptly describes the compartments of such a structure1 as can be seen by a glance at ,fig4 #g1 and this term has been retained even till to-day in spite of the fact that its original significance has entirely disappeared4 ,during the last century not a few naturalists observed and described these little vesicles1 always regarding them as little spaces and never looking upon them as having any significance in the activities of plants4 ,in one or two instances similar bodies were noticed in animals1 although no connection was drawn between them and the cells of plants4 ,in the early part of the century observations upon various kinds of animals and plant tissues multiplied1 and many microscopists independently announced the discovery of similar small corpuscular bodies4 ,finally1 in #ahci1 these observations were combined together by ,schwann into one general theory4 ,according to the cell doctrine then formulated1 the parts of all animals and plants are either composed of cells or of material derived from cells4 ,the bark1 the wood1 the roots1 the leaves of plants are all composed of little vesicles similar to those already described under the name of cells4 ,in animals the cellular structure is not so easy to make out2 but here too the muscle1 the bone1 the nerve1 the gland are all made up of similar vesicles or of material made from them4 ,the cells are of wonderfully different shapes and widely different sizes1 but in general structure they are alike4 ,these cells1 thus found in animals and plants alike1 formed the first connecting link between animals and plants4 ,this discovery was like that of our supposed supramundane observer when he first found the human being that brought into connection the widely different cities in the various parts of the world4 ,illustration3 ,,fig4 #g4--;,a bit of bark showing cellular structure4 ,schwann and his immediate followers1 while recognizing that the bodies of animals and plants were composed of cells1 were at a loss to explain how these cells arose4 ,the belief held at first was that there existed in the bodies of animals and plants a structureless substance which formed the basis out of which the cells develop1 in somewhat the same way that crystals arise from a mother liquid4 ,this supposed substance ,schwann called the cytoblastema1 and he thought it existed between the cells or sometimes within them4 ,for example1 the fluid part of the blood is the cytoblastema1 the blood corpuscles being the cells4 ,from this structureless fluid the cells were supposed to arise by a process akin to crystallization4 ,to be sure1 the cells grow in a manner very different from that of a crystal4 ,a crystal always grows by layers being added upon its outside1 while the cells grow by additions within its body4 ,but this was a minor detail1 the essential point being that from a structureless liquid containing proper materials the organized cell separated itself4 ,this idea of the cytoblastema was early thrown into suspicion1 and almost at the time of the announcement of the cell doctrine certain microscopists made the claim that these cells did not come from any structureless medium1 but by division from other cells like themselves4 ,this claim1 and its demonstration1 was of even greater importance than the discovery of the cells4 ,for a number of years1 however1 the matter was in dispute1 evidence being collected which about equally attested each view4 ,it was a ,scotchman1 ,dr4 ,barry1 who finally produced evidence which settled the question from the study of the developing egg4 ,the essence of his discovery was as follows3 ,the ovum of an animal is a single cell1 and when it begins to develop into an embryo it first simply divides into two halves1 producing two cells 7,fig1 #h1 a and b74 ,each of these in turn divides1 giving four1 and by repeated divisions of this kind there arises a solid mass of smaller cells 7,fig4 #h1 b to f17 called the mulberry stage1 from its resemblance to a berry4 ,this is1 of course1 simply a mass of cells1 each derived by division from the original4 ,as the cells increase in number1 the mass also increases in size by the absorption of nutriment1 and the cells continue dividing until the mass contains thousands of cells4 ,meantime the body of the animal is formed out of these cells1 and when it is adult it consists of millions of cells1 all of which have been derived by division from the original cell4 ,in such a history each cell comes from pre-existing cells and a cytoblastema plays no part4 ,illustration3 ,,fig4 #h4--,successive stages in the division of the developing egg4 ,it was impossible1 however1 for ,barry or any other person to follow the successive divisions of the egg cell through all the stages to the adult4 ,the divisions can be followed for a short time under the microscope1 but the rest must be a matter of simple inference4 ,it was argued that since cell origin begins in this way by simple division1 and since the same process can be observed in the adult1 it is reasonable to assume that the same process has continued uninterruptedly1 and that this is the only method of cell origin4 ,but a final demonstration of this conclusion was not forthcoming for a long time4 ,for many years some biologists continued to believe that cells can have other origin than from pre-existing cells4 ,year by year has the evidence for such free cell origin become less1 until the view has been entirely abandoned1 and to-day it is everywhere admitted that new cells always arise from old ones by direct descent1 and thus every cell in the body of an animal or plant is a direct descendant by division from the original egg cell4 ,the ,cell4--,but what is this cell which forms the unit of life1 and to which all the fundamental vital properties can be traced8 ,we will first glance at the structure of the cell as it was understood by the earlier microscopists4 ,a typical cell is shown in ,fig4 #i4 ,it will be seen that it consists of three quite distinct parts4 ,there is first the cell wall 7cw7 which is a limiting membrane of varying thickness and shape4 ,this is in reality lifeless material1 and is secreted by the rest of the cell4 ,being thus produced by the other active parts of the cell1 we will speak of it as formed material in distinction from the rest1 which is active material4 ,inside this vesicle is contained a somewhat transparent semifluid material which has received various names1 but which for the present we will call cell substance 7,fig4 #i1 pr74 ,it may be abundant or scanty1 and has a widely varying consistency from a very liquid mass to a decidedly thick jellylike substance4 ,lying within the cell substance is a small body1 usually more or less spherical in shape1 which is called the nucleus 7,fig4 #i1 n74 ,it appears to the microscope similar to the cell substance in character1 and has frequently been described as a bit of the cell substance more dense than the remainder4 ,lying within the nucleus there are usually to be seen one or more smaller rounded bodies which have been called nucleoli4 ,from the very earliest period that cells have been studied1 these three parts1 cell wall1 cell substance1 and nucleus have been recognized1 but as to their relations to each other and to the general activities of the cell there has been the widest variety of opinion4 ,illustration3 ,,fig4 #i4--;,a cell2 cw is the cell wall2 pr1 the cell substance2 n1 the nucleus4 ,cellular ,structure of ,organisms4--,it will be well to notice next just what is meant by saying that all living bodies are composed of cells4 ,this can best be understood by referring to the accompanying figures4 ,figs4 #aj-ad1 for instance1 show the microscopic appearance of several plant tissues4 ,illustration3 ,,fig4 #aj4--;,cells at a root tip4 ,illustration3 ,,fig4 #aa4--,section of a leaf showing cells of different shapes4 ,at ,fig4 #aj will be seen the tip of a root1 plainly made of cells quite similar to the typical cell described4 ,at ,fig4 #aa will be seen a bit of a leaf showing the same general structure4 ,at ,fig4 #ab is a bit of plant tissue of which the cell walls are very thick1 so that a very dense structure is formed4 ,at ,fig4 #ac is a bit of a potato showing its cells filled with small granules of starch which the cells have produced by their activities and deposited within their own bodies4 ,at ,fig4 #ad are several wood cells showing cell walls of different shape which1 having become dead1 have lost their contents and simply remain as dead cell walls4 ,each was in its earlier history filled with cell substance and contained a nucleus4 ,in a similar way any bit of vegetable tissue would readily show itself to be made of similar cells4 ,in animal tissues the cellular structure is not so easily seen1 largely because the products made by the cells1 the formed products1 become relatively more abundant and the cells themselves not so prominent4 ,but the cellular structure is none the less demonstrable4 ,in ,fig4 #ae1 for instance1 will be seen a bit of cartilage where the cells themselves are rather small1 while the material deposited between them is abundant4 ,this material between the cells is really to be regarded as an excessively thickened cell wall and has been secreted by the cell substance lying within the cells1 so that a bit of cartilage is really a mass of cells with an exceptionally thick cell wall4 ,at ,fig4 #af is shown a little blood4 ,here the cells are to be seen floating in a liquid4 ,the liquid is colourless and it is the red colour in the blood cells which gives the blood its red colour4 ,the liquid may here again be regarded as material produced by cells4 ,at ,fig4 #ag is a bit of bone showing small irregular cells imbedded within a large mass of material which has been deposited by the cell4 ,in this case the formed material has been hardened by calcium phosphate1 which gives the rigid consistency to the bone4 ,in some animal tissues the formed material is still greater in amount4 ,at ,fig4 #ah1 for example1 is a bit of connective tissue1 made up of a mass of fine fibres which have no resemblance to cells1 and indeed are not cells4 ,these fibres have1 however1 been made by cells1 and a careful study of such tissue at proper places will show the cells within it4 ,the cells shown in ,fig4 #ah 7c7 have secreted the fibrous material4 ,fig4 #ai shows a cell composing a bit of nerve4 ,at ,fig4 #bj is a bit of muscle2 the only trace of cellular structure that it shows is in the nuclei 7n71 but if the muscle be studied in a young condition its cellular structure is more evident4 ,thus it happens in adult animals that the cells which are large and clear at first1 become less and less evident1 until the adult tissue seems sometimes to be composed mostly of what we have called formed material4 ,illustration3 ,,fig4 #ab4--,plant cells with thick walls1 from a fern4 ,illustration3 ,,fig4 #ac4--,section of a potato showing different shaped cells1 the inner and larger ones being filled with grains of starch4 ,illustration3 ,,fig4 #ad4--,various shaped wood cells from plant tissue4 ,illustration3 ,,fig4 #ae4--;,a bit of cartilage4 ,illustration3 ,,fig4 #af4--;,frog's blood3 a and b are the cells2 c is the liquid4 ,illustration3 ,,fig4 #ag4--;,a bit of bone1 showing the cells imbedded in the bony matter4 ,it must not be imagined1 however1 that a very rigid line can be drawn between the cell itself and the material it forms4 ,the formed material is in many cases simply a thickened cell wall1 and this we commonly regard as part of the cell4 ,in many cases the formed material is simply the old dead cell walls from which the living substance has been withdrawn 7,fig4 #ad74 ,in other cases the cell substance acquires peculiar functions1 so that what seems to be the formed material is really a modified cell body and is still active and alive4 ,such is the case in the muscle4 ,in other cases the formed material appears to be manufactured within the cell and secreted1 as in the case of bone4 ,no sharp lines can be drawn1 however1 between the various types4 ,but the distinction between formed material and cell body is a convenient one and may well be retained in the discussion of cells4 ,in our discussion of the fundamental vital properties we are only concerned in the cell substance1 the formed material having nothing to do with fundamental activities of life1 although it forms largely the secondary machinery which we have already studied4 ,illustration3 ,,fig4 #ah4--;,connective tissue4 ,the cells of the tissue are shown at c1 and the fibres or formed matter at f4 ,in all higher animals and plants the life of the individual begins as a single ovum or a single cell1 and as it grows the cells increase rapidly until the adult is formed out of hundreds of millions of cells4 ,as these cells become numerous they cease1 after a little1 to be alike4 ,they assume different shapes which are adapted to the different duties they are to perform4 ,thus1 those cells which are to form bone soon become different from those which are to form muscle1 and those which are to form the blood are quite unlike those which are to produce the hairs4 ,by means of such a differentiation there arises a very complex mass of cells1 with great variety in shape and function4 ,illustration3 ,,fig4 #ai4 ,a piece of nerve fibre1 showing the cell with its nucleus at n4 ,it should be noticed further that there are some animals and plants in which the whole animal is composed of a single cell4 ,these organisms are usually of extremely minute size1 and they comprise most of the so-called animalcul which are found in water4 ,in such animals the different parts of the cell are modified to perform different functions4 ,the different organs appear within the cell1 and the cell is more complex than the typical cell described4 ,fig4 #ba shows such a cell4 ,such an animal possesses several organs1 but1 since it consists of a single mass of protoplasm and a single nucleus1 it is still only a single cell4 ,in the multicellular organisms the organs of the body are made up of cells1 and the different organs are produced by a differentiation of cells1 but in the unicellular organisms the organs are the results of the differentiation of the parts of a single cell4 ,in the one case there is a differentiation of cells1 and in the other of the parts of a cell4 ,illustration3 ,,fig4 #bj4--;,a muscle fibre4 ,the nucleii are shown at n4 ,illustration3 ,,fig4 #ba4--;,a complex cell4 ,it is an entire animal1 but composed of only one cell4 ,such1 in brief1 is the cell to whose activities it is possible to trace the fundamental properties of all living things4 ,cells are endowed with the properties of irritability1 contractibility1 assimilation and reproduction1 and it is thus plainly to the study of cells that we must look for an interpretation of life phenomena4 ,if we can reach an intelligible understanding of the activities of the cell our problem is solved1 for the activities of the fully formed animal or plant1 however complex1 are simply the application of mechanical and chemical principles among the groups of such cells4 ,but wherein does this knowledge of cells help us8 ,are we any nearer to understanding how these vital processes arise8 ,in answer to this question we may first ask whether it is possible to determine whether any one part of the cell is the seat of its activities4 ,the ,cell ,wall4--,the first suggestion which arose was that the cell wall was the important part of the cell1 the others being secondary4 ,this was not an unnatural conclusion4 ,the cell wall is the most persistent part of the cell4 ,it was the part first discovered by the microscope and is the part which remains after the other parts are gone4 ,indeed1 in many of the so-called cells the cell wall is all that is seen1 the cell contents having disappeared 7,fig4 #ad74 ,it was not strange1 then1 that this should at first have been looked upon as the primary part4 ,the idea was that the cell wall in some way changed the chemical character of the substances in contact with its two sides1 and thus gave rise to vital activities which1 as we have seen1 are fundamentally chemical4 ,thus the cell wall was regarded as the most essential part of the cell1 since it controlled its activities4 ,this the belief of ,schwann1 although he also regarded the other parts of the cell as of importance4 ,illustration3 ,,fig4 #bb4--;,an amoeba4 ,a single cell without cell wall4 n is the nucleus2 f1 a bit of food which the cell has absorbed4 ,this conception1 however1 was quite temporary4 ,it was much as if our hypothetical supramundane observer looked upon the clothes of his newly discovered human being as forming the essential part of his nature4 ,it was soon evident that this position could not be maintained4 ,it was found that many bits of living matter were entirely destitute of cell wall4 ,this is especially true of animal cells4 ,while among plants the cell wall is almost always well developed1 it is very common for animal cells to be entirely lacking in this external covering--as1 for example1 the white blood-cells4 ,fig4 #bb shows an amoeba1 a cell with very active powers of motion and assimilation1 but with no cell wall4 ,moreover1 young cells are always more active than older ones1 and they commonly possess either no cell wall or a very slight one1 this being deposited as the cell becomes older and remaining long after it is dead4 ,such facts soon disproved the notion that the cell wall is a vital part of the cell1 and a new conception took its place which was to have a more profound influence upon the study of living things than any discovery hitherto made4 ,this was the formulation of the doctrine of the nature of protoplasm4 ,protoplasm4--7a7 ,discovery4 ,as it became evident that the cell wall is a somewhat inactive part of the cell1 more attention was put on the cell contents4 ,for twenty years after the formulation of the cell doctrine both the cell substance and the nucleus had been looked upon as essential to its activities4 ,this was more especially true of the nucleus1 which had been thought of as an organ of reproduction4 ,these suggestions appeared indefinitely in the writings of one scientist and another1 and were finally formulated in #ahfj into a general theory which formed what has sometimes been called the starting point of modern biology4 ,from that time the material known as protoplasm was elevated into a prominent position in the discussion of all subjects connected with living phenomena4 ,the idea of protoplasm was first clearly defined by ,schultze1 who claimed that the real active part of the cell was the cell substance within the cell wall4 ,this substance he proved to be endowed with powers of motion and powers of inducing chemical changes associated with vital phenomena4 ,he showed it to be the most abundant in the most active cells1 becoming less abundant as the cells lose their activity1 and disappearing when the cells lose their vitality4 ,this cell substance was soon raised into a position of such importance that the smaller body within it was obscured1 and for some twenty years more the nucleus was silently ignored in biological discussion4 ,according to ,schultze1 the cell substance itself constituted the cell1 the other parts being entirely subordinate1 and indeed frequently absent4 ,a cell was thus a bit of protoplasm1 and nothing more4 ,but the more important feature of this doctrine was not the simple conclusion that the cell substance constitutes the cell1 but the more sweeping conclusion that this cell substance is in all cells essentially identical4 ,the study of all animals1 high and low1 showed all active cells filled with a similar material1 and more important still1 the study of plant cells disclosed a material strikingly similar4 ,schultze experimented with this material by all means at his command1 and finding that the cell substance in all animals and plants obeys the same tests1 reached the conclusion that the cell substance in animals and plants is always identical4 ,to this material he now gave the name protoplasm1 choosing a name hitherto given to the cell contents of plant cells4 ,from this time forth this term protoplasm was applied to the living material found in all cells1 and became at once the most important factor in the discussion of biological problems4 ,the importance of this newly formulated doctrine it is difficult to appreciate4 ,here1 in protoplasm had been apparently found the foundation of living phenomena4 ,here was a substance universally present in animals and plants1 simple and uniform--a substance always present in living parts and disappearing with death4 ,it was the simplest thing that had life1 and indeed the only thing that had life1 for there is no life outside of cells and protoplasm4 ,but simple as it was it had all the fundamental properties of living things--irritability1 contractibility1 assimilation1 and reproduction4 ,it was a compound which seemingly deserved the name of physical basis of life1 which was soon given to it by ,huxley4 ,with this conception of protoplasm as the physical basis of life the problems connected with the study of life became more simplified4 ,in order to study the nature of life it was no longer necessary to study the confusing mass of complex organs disclosed to us by animals and plants1 or even the somewhat less confusing structures shown by individual cells4 ,even the simple cell has several separate parts capable of undergoing great modifications in different types of animals4 ,this confusion now appeared to vanish1 for only one thing was found to be alive1 and that was apparently very simple4 ,but that substance exhibited all the properties of life4 ,it moved1 it could grow1 and reproduce itself1 so that it was necessary only to explain this substance and life would be explained4 7b7 ,nature of ,protoplasm4--,what is this material1 protoplasm8 ,as disclosed by the early microscope it appeared to be nothing more than a simple mass of jelly1 usually transparent1 more or less consistent1 sometimes being quite fluid1 and at others more solid4 ,structure it appeared to have none4 ,its chief peculiarity1 so far as physical characters were concerned1 was a wonderful and never-ceasing activity4 ,this jellylike material appeared to be endowed with wonderful powers1 and yet neither physical nor microscopical study revealed at first anything more than a uniform homogeneous mass of jelly4 ,chemical study of the same substance was of no less interest than the microscopical study4 ,of course it was no easy matter to collect this protoplasm in sufficient quantity and pure enough to make a careful analysis4 ,the difficulties were in time1 however1 overcome1 and chemical study showed protoplasm to be a proteid1 related to other proteids like albumen1 but one which was more complex than any other known4 ,it was for a long time looked upon by many as a single definite chemical compound1 and attempts were made to determine its chemical formula4 ,such an analysis indicated a molecule made up of several hundred atoms4 ,chemists did not1 however1 look with much confidence upon these results1 and it is not surprising that there was no very close agreement among them as to the number of atoms in this supposed complex molecule4 ,moreover1 from the very first1 some biologists thought protoplasm to be not one1 but more likely a mixture of several substances4 ,but although it was more complex than any other substance studied1 its general characters were so like those of albumen that it was uniformly regarded as a proteid2 but one which was of a higher complexity than others1 forming perhaps the highest number of a series of complex chemical compounds1 of which ordinary proteids1 such as albumen1 formed lower members4 ,thus1 within a few years following the discovery of protoplasm there had developed a theory that living phenomena are due to the activities of a definite though complex chemical compound1 composed chiefly of the elements carbon1 oxygen1 hydrogen1 and nitrogen1 and closely related to ordinary proteids4 ,this substance was the basis of living activity1 and to its modification under different conditions were due the miscellaneous phenomena of life4 7c7 ,significance of ,protoplasm4--,the philosophical significance of this conception was very far-reaching4 ,the problem of life was so simplified by substituting the simple protoplasm for the complex organism that its solution seemed to be not very difficult4 ,this idea of a chemical compound as the basis of all living phenomena gave rise in a short time to a chemical theory of life which was at least tenable1 and which accounted for the fundamental properties of life4 ,that theory1 the chemical theory of life1 may be outlined somewhat as follows3 ,the study of the chemical nature of substances derived from living organisms has developed into what has been called organic chemistry4 ,organic chemistry has shown that it is possible to manufacture artificially many of the compounds which are called organic1 and which had been hitherto regarded as produced only by living organisms4 ,at the beginning of the century1 it was supposed to be impossible to manufacture by artificial means any of the compounds which animals and plants produce as the result of their life4 ,but chemists were not long in showing that this position is untenable4 ,many of the organic products were soon shown capable of production by artificial means in the chemist's laboratory4 ,these organic compounds form a series beginning with such simple bodies as carbonic acid 7,,co#b71 water 7,h#b,o71 and ammonia 7,,nh#c71 and passing up through a large number of members of greater and greater complexity1 all composed1 however1 chiefly of the elements carbon1 oxygen1 hydrogen1 and nitrogen4 ,our chemists found that starting with simple substances they could1 by proper means1 combine them into molecules of greater complexity1 and in so doing could make many of the compounds that had hitherto been produced only as a result of living activities4 ,for example1 urea1 formic acid1 indigo1 and many other bodies1 hitherto produced only by animals and plants1 were easily produced by the chemist by purely chemical methods4 ,now when protoplasm had been discovered as the physical basis of life1 and1 when it was further conceived that this substance is a proteid related to albumens1 it was inevitable that a theory should arise which found the explanation of life in accordance with simple chemical laws4 ,if1 as chemists and biologists then believe1 protoplasm is a compound which stands at the head of the organic series1 and if1 as is the fact1 chemists are each year succeeding in making higher and higher members of the series1 it is an easy assumption that some day they will be able to make the highest member of the series4 ,further1 it is a well-known fact that simple chemical compounds have simple physical properties1 while the higher ones have more varied properties4 ,water has the property of being liquid at certain temperatures and solid at others1 and of dividing into small particles 7i4e41 dissolving7 certain bodies brought in contact with it4 ,the higher compound albumen has1 however1 a great number of properties and possibilities of combination far beyond those of water4 ,now if the properties increase in complexity with the complexity of the compound1 it is again an easy assumption that when we reach a compound as complex as protoplasm1 it will have properties as complex as those of the simple life substance4 ,nor was this such a very wild hypothesis4 ,after all1 the fundamental life activities may all be traced to the simple oxidation of food1 for this results in movement1 assimilation1 and growth1 and the result of growth is reproduction4 ,it was therefore only necessary for our biological chemists to suppose that their chemical compound protoplasm possessed the power of causing certain kinds of oxidation to take place1 just as water itself induces a simpler kind of oxidation1 and they would have a mechanical explanation of the life activities4 ,it was certainly not a very absurd assumption to make1 that this substance protoplasm could have this power1 and from this the other vital activities are easily derived4 ,in other words1 the formulation of the doctrine of protoplasm made it possible to assume that life is not a distinct force1 but simply a name given to the properties possessed by that highly complex chemical compound protoplasm4 ,just as we might give the name aquacity to the properties possessed by water1 so we have actually given the name vitality to the properties possessed by protoplasm4 ,to be sure1 vitality is more marvelous than aquacity1 but so is protoplasm a more complex compound than water4 ,this compound was a very unstable compound1 just as is a mass of gunpowder1 and hence it is highly irritable1 also like gunpowder1 and any disturbance of its condition produces motion1 just as a spark will do in a mass of gunpowder4 ,it is capable of inducing oxidation in foods1 something as water induces oxidation in a bit of iron4 ,the oxidation is1 however1 of a different kind1 and results in the formation of different chemical combinations2 but it is the basis of assimilation4 ,since now assimilation is the foundation of growth and reproduction1 this mechanical theory of life thus succeeded in tracing to the simple properties of the chemical compound protoplasm1 all the fundamental properties of life4 ,since further1 as we have seen in our first chapter1 the more complex properties of higher organisms are easily deduced from these simple ones by the application of the laws of mechanics1 we have here in this mechanical theory of life the complete reduction of the body to a machine4 ,the ,reign of ,protoplasm4--,this substance protoplasm became now naturally the centre of biological thought4 ,the theory of protoplasm arose at about the same time that the doctrine of evolution began to be seriously discussed under the stimulus of ,darwin1 and naturally these two great conceptions developed side by side4 ,evolution was constantly teaching that natural forces are sufficient to account for many of the complex phenomena which had hitherto been regarded as insolvable2 and what more natural than the same kind of thinking should be applied to the vital activities manifested by this substance protoplasm4 ,while the study of plants and animals was showing scientists that natural forces would explain the origin of more complex types from simpler ones through the law of natural selection1 here in this conception of protoplasm was a theory which promised to show how the simplest forms may have been derived from the non-living4 ,for an explanation of the origin of life by natural means appeared now to be a simple matter4 ,it required now no violent stretch of the imagination to explain the origin of life something as follows3 ,we know that the chemical elements have certain affinities for each other1 and will unite with each other under proper conditions4 ,we know that the methods of union and the resulting compounds vary with the conditions under which the union takes place4 ,we know further that the elements carbon1 hydrogen1 oxygen1 and nitrogen have most remarkable properties1 and unite to form an almost endless series of remarkable bodies when brought into combination under different conditions4 ,we know that by varying the conditions the chemist can force these elements to unite into a most extraordinary variety of compounds with an equal variety of properties4 ,what more natural1 then1 than the assumption that under certain conditions these same elements would unite in such a way as to form this compound protoplasm2 and then1 if the ideas concerning protoplasm were correct1 this body would show the properties of protoplasm1 and therefore be alive4 ,certainly such a supposition was not absurd1 and viewed in the light of the rapid advance in the manufacture of organic compounds could hardly be called improbable4 ,chemists beginning with simple bodies like ,,co#b and ,h#b,o were climbing the ladder1 each round of which was represented by compounds of higher complexity4 ,at the top was protoplasm1 and each year saw our chemists nearer the top of the ladder1 and thus approaching protoplasm as their final goal4 ,they now began to predict that only a few more years would be required for chemists to discover the proper conditions1 and thus make protoplasm4 ,as late as #ahhj the prediction was freely made that the next great discovery would be the manufacture of a bit of protoplasm by artificial means1 and thus in the artificial production of life4 ,the rapid advance in organic chemistry rendered this prediction each year more and more probable4 ,the ability of chemists to manufacture chemical compounds appeared to be unlimited1 and the only question in regard to their ability to make protoplasm thus resolved itself into the question of whether protoplasm is really a chemical compound4 ,we can easily understand how eager biologists became now in pursuit of the goal which seemed almost within their reach2 how interested they were in any new discovery1 and how eagerly they sought for lower and simpler types of protoplasm since these would be a step nearer to the earliest undifferentiated life substance4 ,indeed so eager was this pursuit for pure undifferentiated protoplasm1 that it led to one of those unfounded discoveries which time showed to be purely imaginary4 ,when this reign of protoplasm was at its height and biologists were seeking for even greater simplicity a most astounding discovery was announced4 ,the ,british exploring ship ,challenger had returned from its voyage of discovery and collection1 and its various treasures were turned over to the different scientists for study4 ,the brilliant ,prof4 ,huxley1 who had first formulated the mechanical theory of life1 now startled the biological world with the statement that these collections had shown him that at the bottom of the deep sea1 in certain parts of the world1 there exists a diffused mass of living undifferentiated protoplasm4 ,so simple and undifferentiated was it that it was not divided into cells and contained no nucleii4 ,it was1 in short1 exactly the kind of primitive protoplasm which the evolutionist wanted to complete his chain of living structures1 and the biologist wanted to serve as a foundation for his mechanical theory of life4 ,if such a diffused mass of undifferentiated protoplasm existed at the bottom of the sea1 one could hardly doubt that it was developed there by some purely natural forces4 ,the discovery was a startling one1 for it seemed that the actual starting point of life had been reached4 ,huxley named his substance ,bathybias1 and this name became in a short time familiar to every one who was thinking of the problems of life4 ,but the discovery was suspected from the first1 because it was too closely in accord with speculation1 and it was soon disproved4 ,its discoverer soon after courageously announced to the world that he had been entirely mistaken1 and that the ,bathybias1 so far from being undifferentiated protoplasm1 was not an organic product at all1 but simply a mineral deposit in the sea water made by purely artificial means4 ,bathybias stands therefore as an instance of a too precipitate advance in speculation1 which led even such a brilliant man as ,prof4 ,huxley into an unfortunate error of observation2 for1 beyond question1 he would never have made such a mistake had he not been dominated by his speculative theories as to the nature of protoplasm4 ,but although ,bathybias proved delusive1 this did not materially affect the advance and development of the doctrine of protoplasm4 ,simple forms of protoplasm were found1 although none quite so simple as the hypothetical ,bathybias4 ,the universal presence of protoplasm in the living parts of all animals and plants and its manifest activities completely demonstrated that it was the only living substance1 and as the result of a few years of experiment and thought the biologist's conception of life crystallized into something like this3 ,living organisms are made of cells1 but these cells are simply minute independent bits of protoplasm4 ,they may contain a nucleus or they may not1 but the essence of the cell is the protoplasm1 this alone having the fundamental activities of life4 ,these bits of living matter aggregate themselves together into groups to form colonies4 ,such colonies are animals or plants4 ,the cells divide the work of the colony among themselves1 each cell adopting a form best adapted for the special work it has to do4 ,the animal or plant is thus simply an aggregate of cells1 and its activities are the sum of the activities of its separate cells2 just as the activities of a city are the sum of the activities of its individual inhabitants4 ,the bit of protoplasm was the unit1 and this was a chemical compound or a simple mixture of compounds to whose combined physical properties we have given the name vitality4 ,the ,decline of the ,reign of ,protoplasm4--,hardly had this extreme chemical theory of life been clearly conceived before accumulating facts began to show that it is untenable and that it must at least be vastly modified before it can be received4 ,the foundation of the chemical theory of life was the conception that protoplasm is a definite though complex chemical compound4 ,but after a few years' study it appeared that such a conception of protoplasm was incorrect4 ,it had long been suspected that protoplasm was more complex than was at first thought4 ,it was not even at the outset found to be perfectly homogeneous1 but was seen to contain minute granules1 together with bodies of larger size4 ,although these bodies were seen they were regarded as accidental or secondary1 and were not thought of as forming any serious objection to the conception of protoplasm as a definite chemical compound4 ,but modern opticians improved their microscopes1 and microscopists greatly improved their methods4 ,with the new microscopes and new methods there began to appear1 about twenty years ago1 new revelations in regard to this protoplasm4 ,its lack of homogeneity became more evident1 until there has finally been disclosed to us the significant fact that protoplasm is to be regarded as a substance not only of chemical but also of high mechanical complexity4 ,the idea of this material as a simple homogeneous compound or as a mixture of such compounds is absolutely fallacious4 ,protoplasm is to-day known to be made up of parts harmoniously adapted to each other in such a way as to form an extraordinarily intricate machine2 and the microscopist of to-day recognizes clearly that the activities of this material must be regarded as the result of the machinery which makes up protoplasm rather than as the simple result of its chemical composition4 ,protoplasm is a machine and not a chemical compound4 ,illustration3 ,,fig4 #bc4--;,a cell as it appears to the modern microscope4 a1 protoplasmic reticulum2 b1 liquid in its meshes2 c1 nuclear membrane2 d1 nuclear reticulum2 e1 chromatin reticulum2 f1 nucleolus2 g1 centrosome2 h1 centrosphere2 i1 vacuole2 j1 inert bodies4 ,structure of ,protoplasm4--,the structure of protoplasm is not yet thoroughly understood by scientists1 but a few general facts are known beyond question4 ,it is thought1 in the first place1 that it consists of two quite different substances4 ,there is a somewhat solid material permeating it1 usually1 regarded as having a reticulate structure4 ,it is variously described1 sometimes as a reticulate network1 sometimes as a mass of threads or fibres1 and sometimes as a mass of foam 7,fig4 #bc1 a74 ,it is extremely delicate and only visible under special conditions and with the best of microscopes4 ,only under peculiar conditions can it be seen in protoplasm while alive4 ,there is no question1 however1 that all protoplasm is permeated when alive by a minute delicate mass of material1 which may take the form of threads or fibres or may assume other forms4 ,within the meshes of this thread or reticulum there is found a liquid1 perfectly clear and transparent1 to whose presence the liquid character of the protoplasm is due 7,fig4 #bc1 b74 ,in this liquid no structure can be determined1 and1 so far as we know1 it is homogeneous4 ,still further study discloses other complexities4 ,it appears that the fibrous material is always marked by the presence of excessively minute bodies1 which have been called by various names1 but which we will speak of as microsomes4 ,sometimes1 indeed1 the fibres themselves appear almost like strings of beads1 so that they have been described as made up of rows of minute elements4 ,it is immaterial for our purpose1 however1 whether the fibres are to be regarded as made up of microsomes or not4 ,this much is sure1 that these microsomes --granules of excessive minuteness--occur in protoplasm and are closely connected with the fibres 7,fig4 #bc1 a74 ,the ,nucleus4--7a7 ,presence of a ,nucleus4--,if protoplasm has thus become a new substance in our minds as the result of the discoveries of the last twenty years1 far more marvelous have been the discoveries made in connection with that body which has been called the nucleus4 ,even by the early microscopists the nucleus was recognized1 and during the first few years of the cell doctrine it was frequently looked upon as the most active part of the cell and as especially connected with its reproduction4 ,the doctrine of protoplasm1 however1 so captivated the minds of biologists that for quite a number of years the nucleus was ignored1 at least in all discussions connected with the nature of life4 ,it was a body in the cell whose presence was unexplained and which did not fall into accord with the general view of protoplasm as the physical basis of life4 ,for a while1 therefore1 biologists gave little attention to it1 and were accustomed to speak of it simply as a bit of protoplasm a little more dense than the rest4 ,the cell was a bit of protoplasm with a small piece of more dense protoplasm in its centre appearing a little different from the rest and perhaps the most active part of the cell4 ,as a result of this excessive belief in the efficiency of protoplasm the question of the presence of a nucleus in the cell was for a while looked upon as one of comparatively little importance4 ,many cells were found to have nucleii while others did not show their presence1 and microscopists therefore believed that the presence of a nucleus was not necessary to constitute a cell4 ,a ,german naturalist recognized among lower animals one group whose distinctive characteristic was that they were made of cells without nucleii1 giving the name ,monera to the group4 ,as the method of studying cells improved microscopists learned better methods of discerning the presence of the nucleus1 and as it was done little by little they began to find the presence of nucleii in cells in which they had hitherto not been seen4 ,as microscopists now studied one after another of these animals and plants whose cells had been said to contain no nucleus1 they began to find nucleii in them1 until the conclusion was finally reached that a nucleus is a fundamental part of all active cells4 ,old cells which have lost their activity may not show nucleii1 but1 so far as we know1 all active cells possess these structures1 and apparently no cell can carry on its activity without them4 ,some cells have several nucleii1 and others have the nuclear matter scattered through the whole cell instead of being aggregated into a mass2 but nuclear matter the cell must have to carry on its life4 ,illustration3 ,,fig4 #bd4--;,a cell cut into three pieces1 each containing a bit of the nucleus4 ,each continues its life indefinitely1 soon acquiring the form of the original as at ,c4 ,later the experiment was made of depriving cells of their nucleii1 and it still further emphasized the importance of the nucleus4 ,among unicellular animals are some which are large enough for direct manipulation1 and it is found that if these cells are cut into pieces the different pieces will behave very differently in accordance with whether or not they have within them a piece of the nucleus4 ,all the pieces are capable of carrying on their life activities for a while4 ,the pieces of the cell which contain the nucleus of the original cell1 or even a part of it1 are capable of carrying on all its life activities perfectly well4 ,in ,fig4 #bd is shown such a cell cut into three pieces1 each of which contains a piece of the nucleus4 ,each carries on its life activities1 feeds1 grows and multiplies perfectly well1 the life processes seeming to continue as if nothing had happened4 ,quite different is it with fragments which contain none of the nucleus 7,fig4 #be74 ,these fragments 7#a and #c71 even though they may be comparatively large masses of protoplasm1 are incapable of carrying on the functions of their life continuously4 ,for a while they continue to move around and apparently act like the other fragments1 but after a little their life ceases4 ,they are incapable of assimilating food and incapable of reproduction1 and hence their life cannot continue very long4 ,facts like these demonstrate conclusively the vital importance of the nucleus in cell activity1 and show us that the cell1 with its power of continued life1 must be regarded as a combination of protoplasm with its nucleus1 and cannot exist without it4 ,it is not protoplasm1 but cell substance1 plus cell nucleus1 which forms the simplest basis of life4 ,illustration3 ,,fig4 #be4--;,a cell cut into three pieces1 only one of which1 ,no4 #b1 contains any nucleus4 ,this fragment soon acquires the original form and continues its life indefinitely1 as shown at ,b4 ,the other two pieces though living for a time1 die without reproducing4 ,as more careful study of protoplasm was made it soon became evident that there is a very decided difference between the nucleus and the protoplasm4 ,the old statement that the nucleus is simply a bit of dense protoplasm is not true4 ,in its chemical and physical composition as well as in its activities the nucleus shows itself to be entirely different from the protoplasm4 ,it contains certain definite bodies not found in the cell substance1 and it goes through a series of activities which are entirely unrepresented in the surrounding protoplasm4 ,it is something entirely distinct1 and its relations to the life of the cell are unique and marvelous4 ,these various facts led to a period in the discussion of biological topics which may not inappropriately be called the ,reign of the ,nucleus4 ,let us1 therefore1 see what this structure is which has demanded so much attention in the last twenty years4 7b7 ,structure of the ,nucleus4--,at first the nucleus appears to be very much like the cell substance4 ,like the latter1 it is made of fibres1 which form a reticulum 7,fig4 #bc71 and these fibres1 like those of protoplasm1 have microsomes in intimate relation with them and hold a clear liquid in their meshes4 ,the meshes of the network are usually rather closer than in the outer cell substance1 but their general character appears to be the same4 ,but a more close study of the nucleus discloses vast differences4 ,in the first place1 the nucleus is usually separated from the cell substance by a membrane 7,fig4 #bc1 c74 ,this membrane is almost always present1 but it may disappear1 and usually does disappear1 when the nucleus begins to divide4 ,within the nucleus we find commonly one or two smaller bodies1 the nucleoli 7,fig4 #bc1 f74 ,they appear to be distinct vital parts of the nucleus1 and thus different from certain other solid bodies which are simply excreted material1 and hence lifeless4 ,further1 we find that the reticulum within the nucleus is made up of two very different parts4 ,one portion is apparently identical with the reticulum of the cell substance 7,fig4 #bc1 d74 ,this forms an extremely delicate network1 whose fibres have chemical relations similar to those of the cell substance4 ,indeed1 sometimes1 the fibres of the nucleus may be seen to pass directly into those of the network of the cell substance1 and hence they are in all probability identical4 ,this material is called linin1 by which name we shall hereafter refer to it4 ,there is1 however1 in the nucleus another material which forms either threads1 or a network1 or a mass of granules1 which is very different from the linin1 and has entirely different properties4 ,this network has the power of absorbing certain kinds of stains very actively1 and is consequently deeply stained when treated as the microscopist commonly prepares his specimens4 ,for this reason it has been named chromatin 7,fig1 #bc1 e71 although in more recent times other names have been given to it4 ,of all parts of the cell this chromatin is the most remarkable4 ,it appears in great variety in different cells1 but it always has remarkable physiological properties1 as will be noticed presently4 ,all things considered1 this chromatin is probably the most remarkable body connected with organic life4 ,illustration3 ,,fig4 #bf4--;,different forms of nucleii4 ,the nucleii of different animals and plants all show essentially the characteristics just described4 ,they all contain a liquid1 a linin network1 and a chromatin thread or network1 but they differ most remarkably in details1 so that the variety among the nucleii is almost endless 7,fig4 #bf74 ,they differ first in their size relative to the size of the cell2 sometimes--especially in young cells--the nucleus being very large1 while in other cases the nucleus is very small and the protoplasmic contents of the cell very large2 finally1 in cells which have lost their activity the nucleus may almost or entirely disappear4 ,they differ1 secondly1 in shape4 ,the typical form appears to be spherical or nearly so2 but from this typical form they may vary1 becoming irregular or elongated4 ,they are sometimes drawn out into long masses looking like a string of beads 7,fig4 #bd71 or1 again1 resembling minute coiled worms 7,fig4 #ba71 while in still other cells they may be branching like the twigs of a tree4 ,the form and shape of the chromatin thread differs widely4 ,sometimes this appears to be mere reticulum 7,fig4 #bc72 at others1 a short thread which is somewhat twisted or coiled 7,fig4 #bf72 while in other cells the chromatin thread is an extremely long1 very much twisted convolute thread so complexly woven into a tangle as to give the appearance of a minute network4 ,the nucleii differ also in the number of nucleoli they contain as well as in other less important particulars4 ,fig4 #bf will give a little notion of the variety to be found among different nucleii2 but although they thus do vary most remarkably in shape in the essential parts of their structure they are alike4 ,centrosome4--,before noticing the activities of the nucleus it will be necessary to mention a third part of the cell4 ,within the last few years there has been found to be present in most cells an organ which has been called the centrosome4 ,this body is shown at ,fig4 #bc1 g4 ,it is found in the cell substance just outside the nucleus1 and commonly appears as an extremely minute rounded dot1 so minute that no internal structure has been discerned4 ,it may be no larger than the minute granules or microsomes in the cell1 and until recently it entirely escaped the notice of microscopists4 ,it has now1 however1 been clearly demonstrated as an active part of the cell and entirely distinct from the ordinary microsomes4 ,it stains differently1 and1 as we shall soon see1 it appears to be in most intimate connection with the center of cell life4 ,in the activities which characterize cell life this centrosome appears to lead the way4 ,from it radiate the forces which control cell activity1 and hence this centrosome is sometimes called the dynamic center of the cell4 ,this leads us to the study of cell activity1 which discloses to us some of the most extraordinary phenomena which have come to the knowledge of science4 ,function of the ,nucleus4--,to understand why it is that the nucleus has taken such a prominent position in modern biological discussion it will be only necessary to notice some of the activities of the cell4 ,of the four fundamental vital properties of cell life the one which has been most studied and in regard to which most is known is reproduction4 ,this knowledge appears chiefly under two heads1 viz41 cell division and the fertilization of the egg4 ,every animal and plant begins its life as a simple cell1 and the growth of the cell into the adult is simply the division of the original cell into parts accompanied by a differentiation of the parts4 ,the fundamental phenomena of growth and reproduction is thus cell division1 and if we can comprehend this process in these simple cells we shall certainly have taken a great step toward the explanation of the mechanics of life4 ,during the last ten years this cell division has been most thoroughly studied1 and we have a pretty good knowledge of it so far as its microscopical features are concerned4 ,the following description will outline the general facts of such cell division1 and will apply with considerable accuracy to all cases of cell division1 although the details may differ not a little4 ,illustration3 ,,fig4 #bg4--,this and the following figures show stages in cell division4 ,fig4 #bg shows the resting stage with the chromatin1 cr1 in the form of a network within the nuclear membrane and the centrosome1 ce1 already divided into two4 ,illustration3 ,,fig4 #bh4--,the chromatin is broken into threads or chromosomes1 cr4 ,the centrosomes show radiating fibres4 ,cell ,division or ,karyokinesis4--,we will begin with a cell in what is called the resting stage1 shown at ,fig4 #bc4 ,such a cell has a nucleus1 with its chromatin1 its membrane1 and linin1 as already described4 ,outside the nucleus is the centrosome1 or1 more commonly1 two of them lying close together4 ,if there is only one it soon divides into two1 and if it has already two1 this is because a single centrosome which the cell originally possessed has already divided into two1 as we shall presently see4 ,this cell1 in short1 is precisely like the typical cell which we have described1 except in the possession of two centrosomes4 ,the first indication of the cell division is shown by the chromatin fibres4 ,during the resting stage this chromatin material may have the form of a thread1 or may form a network of fibres 7see ,fig4 #bg74 ,but whatever be its form during the resting stage1 it assumes the form of a thread as the cell prepares for division4 ,almost at once this thread breaks into a number of pieces known as chromosomes 7,fig4 #bh74 ,it is an extremely important fact that the number of these chromosomes in the ordinary cells of any animal or plant is always the same4 ,in other words1 in all the cells of the body of animal or plant the chromatin material in the nucleus breaks into the same number of short threads at the time that the cell is preparing to divide4 ,the number is the same for all animals of the same species1 and is never departed from4 ,for example1 the number in the ox is always sixteen1 while the number in the lily is always twenty-four4 ,during this process of the formation of the chromosomes the nucleoli disappear1 sometimes being absorbed apparently in the chromosomes1 and sometimes being ejected into the cell body1 where they disappear4 ,whether they have anything to do with further changes is not yet known4 ,the next step in the process of division appears in the region of the centrosomes4 ,each of the two centrosomes appears to send out from itself delicate radiating fibres into the surrounding cell substance 7,fig4 #bh74 ,whether these actually arise from the centrosome or are simply a rearrangement of the fibres in the cell substance is not clear1 but at all events the centrosome becomes surrounded by a mass of radiating fibres which give it a starlike appearance1 or1 more commonly1 the appearance of a double star1 since there are two centrosomes close together 7,fig4 #bh74 ,these radiating fibres1 whether arising from the centrosomes or not1 certainly all centre in these bodies1 a fact which indicates that the centrosomes contain the forces which regulate their appearance4 ,between the two stars or asters a set of fibres can be seen running from one to the other 7,fig4 #bi74 ,these two asters and the centrosomes within them have been spoken of as the dynamic centre of the cell since they appear to control the forces which lead to cell division4 ,in all the changes which follow these asters lead the way4 ,the two asters1 with their centrosomes1 now move away from each other1 always connected by the spindle fibres1 and finally come to lie on opposite sides of the nucleus 7,figs4 #bi1 #cj74 ,when they reach this position they are still surrounded by the radiating fibres1 and connected by the spindle fibres4 ,meantime the membrane around the nucleus has disappeared1 and thus the spindle fibres readily penetrate into the nuclear substance 7,fig4 #cj74 ,illustration3 ,,fig4 #bi4--,the centrosomes are separating but are connected by fibres4 ,illustration3 ,,fig4 #cj4--,the centrosomes are separate and the equatorial plate of chromosomes1 cr1 is between them4 ,during this time the chromosomes have been changing their position4 ,whether this change in position is due to forces within themselves1 or whether they are moved around passively by forces residing in the cell substances1 or whether1 which is the most probable1 they are pulled or pushed around by the spindle fibres which are forcing their way into the nucleus1 is not positively known2 nor is it1 for our purposes1 of special importance4 ,at all events1 the result is that when the asters have assumed their position at opposite poles of the nucleus the chromosomes are arranged in a plane passing through the middle of the nucleus at equal distances from each aster4 ,it seems certain that they are pulled or pushed into this position by forces radiating from the centrosomes4 ,fig4 #cj shows this central arrangement of the chromosomes1 forming what is called the equatorial plate4 ,the next step is the most significant of all4 ,it consists in the splitting of each chromosome into two equal halves4 ,the threads do not divide in their middle but split lengthwise1 so that there are formed two halves identical in every respect4 ,in this way are produced twice the original number of chromosomes1 but all in pairs4 ,the period at which this splitting of the chromosomes occurs is not the same in all cells4 ,it may occur1 as described1 at about the time the asters have reached the opposite poles of the nucleus1 and an equatorial plate is formed4 ,it is not infrequent1 however1 for it to occur at a period considerably earlier1 so that the chromosomes are already divided when they are brought into the equatorial plate4 ,at some period or other in the cell division this splitting of the chromosomes takes place4 ,the significance of the splitting is especially noteworthy4 ,we shall soon find reason for believing that the chromosomes contain all the hereditary traits which the cell hands down from generation to generation1 and indeed that the chromosomes of the egg contain all the traits which the parent hands down to the child4 ,now1 if this chromatin thread consists of a series of units1 each representing certain hereditary characters1 then it is plain that the division of the thread by splitting will give rise to a double series of threads1 each of which has identical characters4 ,should the division occur across the thread the two halves would be unlike1 but taking place as it does by a longitudinal splitting each unit in the thread simply divides in half1 and thus the resulting half threads each contain the same number of similar units as the other and the same as possessed by the original undivided chromosome4 ,this sort of splitting thus doubles the number of chromosomes1 but produces no differentiation of material4 ,illustration3 ,,fig4 #ca4--,stage showing the two halves of the chromosomes separated from each other4 ,illustration3 ,,fig4 #cb4--;,final stage with two nucleii in which the chromosomes have again assumed the form of a network4 ,the centrosomes have divided preparatory to the next division1 and the cell is beginning to divide4 ,the next step in the cell division consists in the separation of the two halves of the chromosomes4 ,each half of each chromosome separates from its fellow1 and moves to the opposite end of the nucleus toward the two centrosomes 7,fig4 #ca74 ,whether they are pulled apart or pushed apart by the spindle fibres is not certain1 although it is apparently sure that these fibres from the centrosomes are engaged in the matter4 ,certain it is that some force exerted from the two centrosomes acts upon the chromosomes1 and forces the two halves of each one to opposite ends of the nucleus1 where they now collect and form two new nucleii1 with evidently exactly the same number of chromosomes as the original1 and with characters identical to each other and to the original 7,fig4 #cb74 ,the rest of the cell division now follows rapidly4 ,a partition grows in through the cell body dividing it into two parts 7,fig4 #cb71 the division passing through the middle of the spindle4 ,in this division1 in some cases at least1 the spindle fibres bear a part--a fact which again points to the importance of the centrosomes and the forces which radiate from them4 ,now the chromosomes in each daughter nucleus unite to form a single thread1 or may diffuse through the nucleus to form a network1 as in ,fig4 #cb4 ,they now become surrounded by a membrane1 so that the new nucleus appears exactly like the original one4 ,the spindle fibres disappear1 and the astral fibres may either disappear or remain visible4 ,the centrosome may apparently in some cases disappear1 but more commonly remains beside the daughter nucleii1 or it may move into the nucleus4 ,eventually it divides into two1 the division commonly occurring at once 7,fig4 #cb71 but sometimes not until the next cell division is about to begin4 ,thus the final result shows two cells each with a nucleus and two centrosomes1 and this is exactly the same sort of structure with which the process began4 7,see ,frontispiece47 ,viewed as a whole1 we may make the following general summary of this process4 ,the essential object of this complicated phenomena of karyokinesis is to divide the chromatin into equivalent halves1 so that the cells resulting from the cell division shall contain an exactly equivalent chromatin content4 ,for this purpose the chromatic elements collect into threads and split lengthwise4 ,the centrosome1 with its fibres1 brings about the separation of these two halves4 ,plainly1 we must conclude that the chromatin material is something of extraordinary importance to the cell1 and the centrosome is a bit of machinery for controlling its division and thus regulating cell division4 ,fertilization of the ,egg4--,this description of cell division will certainly give some idea of the complexity of cell life1 but a more marvelous series of changes still takes place during the time when the egg is preparing for development4 ,inasmuch as this process still further illustrates the nature of the cell1 and has further a most intimate bearing upon the fundamental problem of heredity1 it will be necessary for us to consider it here briefly4 ,the sexual reproduction of the many-celled animals is always essentially alike4 ,a single one of the body cells is set apart to start the next generation1 and this cell1 after separating from the body of the animal or plant which produced it1 begins to divide1 as already shown in ,fig4 #h1 and the many cells which arise from it eventually form the new individual ,this reproductive cell is the egg4 ,but before its division can begin there occurs in all cases of sexual reproduction a process called fertilization1 the essential feature of which is the union of this cell with another commonly from a different individual4 ,while the phenomenon is subject to considerable difference in details1 it is essentially as follows3 ,illustration3 ,,fig4 #cc--;,an egg showing the cell substance and the nucleus1 the latter containing chromosomes in large number and a nucleolus ,the female reproductive cell is called the egg1 and it is this cell which divides to form the next generation4 ,such a cell is shown in ,fig4 #cc4 ,like other cells it has a cell wall1 a cell substance with its linin and fluid portions1 a nucleus surrounded by a membrane and containing a reticulum1 a nucleolus and chromatic material1 and lastly1 a centrosome4 ,now such an egg is a complete cell1 but it is not able to begin the process of division which shall give rise to a new individual until it has united with another cell of quite a different sort and commonly derived from a different individual called the male4 ,why the egg cell is unable to develop without such union with male cell does not concern us here1 but its purpose will be evident as the description proceeds4 ,the egg cell as it comes from the ovary of the female individual is1 however1 not yet ready for union with the male cell1 but must first go through a series of somewhat remarkable changes constituting what is called maturation of the egg4 ,this phenomenon has such an intimate relation to all problems connected with the cell1 that it must be described somewhat in detail4 ,there are considerable differences in the details of the process as it occurs in various animals1 but they all agree in the fundamental points4 ,the following is a general description of the process derived from the study of a large variety of animals and plants4 ,illustration ,fig4 #cd4--,this and the following figures represent the process of fertilization of an egg4 ,in all figures cr is the chromosomes2 cs represents the cell substance 7omitted in the following figures72 mc is the male reproductive cell lying in contact with the egg2 mn is the male nucleus after entering the egg4 ,illustration3 ,,fig4 #ce4--,the egg centrosome has divided1 and the male cell with its centrosome has entered the egg4 ,in the cells of the body of the animal to which this description applies there are four chromosomes ,this is true of all the cells of the animal except the sexual cells4 ,the eggs arise from the other cells of the body1 but during their growth the chromatin splits in such a way that the egg contains double the number of chromosomes1 i4e41 eight 7,fig4 #cd74 ,if this egg should now unite with the other reproductive cell from the male1 the resulting fertilized egg would plainly contain a number of chromosomes larger than that normal for this species of animal4 ,as a result the next generation would have a larger number of chromosomes in each cell than the last generation1 since the division of the egg in development is like that already described and always results in producing new cells with the same number of chromosomes as the starting cell4 ,hence1 if the number of chromosomes in the next generation is to be kept equal to that in the last generation1 this egg cell must get rid of a part of its chromatin material4 ,this is done by a process shown in ,fig4 #ce4 ,the centrosome divides as in ordinary cell division 7,fig4 #ce71 and after rotating on its axis it approaches the surface of the egg 7,figs4 #cf and #cg74 ,the egg now divides 7,fig4 #ch71 but the division is of a peculiar kind4 ,although the chromosomes divide equally the egg itself divides into two very unequal parts1 one part still appearing as the egg and the other as a minute protuberance called the polar cell 7pc' in ,fig4 #ch74 ,the chromosomes do not split as they do in the cell division already described1 but each of these two cells1 the egg and the polar body1 receives four chromosomes 7,fig4 #ch74 ,the result is that the egg has now the normal number of chromosomes for the ordinary cells of the animal in question4 ,but this is still too many1 for the egg is soon to unite with the male cell2 and this male cell1 as we shall see1 is to bring in its own quota of chromosomes4 ,hence the egg must get rid of still more of its chromatin material4 ,consequently1 the first division is followed by a second 7,fig4 #ci71 in which there is again produced a large and a small cell4 ,this division1 like the first1 occurs without any splitting of the chromosomes1 one half of the remaining chromosomes being ejected in this new cell1 the second polar cell 7pc7 leaving the larger cell1 the egg1 with just one half the number of chromosomes normal for the cells of the animal in question4 ,meantime the first pole cell has also divided1 so that we have now1 as shown in ,fig4 #dj1 four cells1 three small and one large1 but each containing one half the normal number of chromosomes4 ,in the example figured1 four is the normal number for the cells of the animal4 ,the egg at the beginning of the process contained eight1 but has now been reduced to two4 ,in the further history of the egg the smaller cells1 called polar cells1 take no part1 since they soon disappear and have nothing to do with the animal which is to result from the further division of the egg4 ,this process of the formation of the polar cells is thus simply a device for getting rid of some of the chromatin material in the egg cell1 so that it may unite with a second cell without doubling the normal number of chromosomes4 ,illustration3 ,,fig4 #ch--;,first division complete and first polar cell formed1 pc'4 ,illustration3 ,,fig4 #ci4--;,formation of the second polar cell1 pc4 ,illustration3 ,,fig4 #dj4--;,completion of the process of extrusion of the chromatic material2 fn shows the two chromosomes retained in the egg forming the female pronucleus4 ,the centrosome has disappeared4 ,previously to this process the other sexual cell1 the spermatozoon1 or male reproductive cell1 has been undergoing a somewhat similar process4 ,this is also a true cell 7,fig4 #cd1 mc71 although it is of a decidedly smaller size than the egg and of a very different shape4 ,it contains cell substance1 a nucleus with chromosomes1 and a centrosome1 the number of chromosomes1 as shown later1 being however only half that normal for the ordinary cells of the animals4 ,the study of the development of the spermatozoon shows that it has come from cells which contained the normal number of four1 but that this number has been reduced to one half by a process which is equivalent to that which we have just noticed in the egg4 ,thus it comes about that each of the sexual elements1 the egg and the spermatozoon1 now contains one half the normal number of chromosomes4 ,illustration3 ,,fig4 #cf--,the egg centrosomes have changed their position4 ,the male cell with its centrosome remains inactive until the stage represented in ,fig4 #db4 ,illustration3 ,,fig4 #cg--;,beginning of the first division for removing superfluous chromosomes4 ,now by some mechanical means these two reproductive cells are brought in contact with each other1 shown in ,fig4 #cd1 and as soon as they are brought into each other's vicinity the male cell buries its head in the body of the egg4 ,the tail by which it has been moving is cast off1 and the head containing the chromosomes and the centrosome enters the egg1 forming what is called the male pronucleus 7,figs4 #ce-ch1 mn74 ,this entrance of the male cell occurs either before the formation of the polar cells of the egg or afterward4 ,if1 however1 it takes place before1 the male pronucleus simply remains dormant in the egg while the polar cells are being protruded1 and not until after that process is concluded does it begin again to show signs of activity which result in the cell union4 ,the further steps in this process appear to be controlled by the centrosome1 although it is not quite certain whence this centrosome is derived4 ,originally1 as we have seen1 the egg contained a centrosome1 and the male cell has also brought a second into the egg 7,fig4 #ce1 ce74 ,in some cases1 and this is true for the worm we are describing1 it is certain that the egg centrosome disappears while that of the spermatozoon is retained alone to direct the further activities 7,fig4 #da74 ,possibly this may be the case in all eggs1 but it is not sure4 ,it is a matter of some little interest to have this settled1 for if it should prove true1 then it would evidently follow that the machinery for cell division1 in the case of sexual reproduction1 is derived from the father1 although the bulk of the cell comes from the mother1 while the chromosomes come from both parents4 ,in the cases where the process has been most carefully studied1 the further changes are as follows3 ,the head of the spermatozoon1 after entrance into the egg1 lies dormant until the egg has thrown off its polar cells1 and thus gotten rid of part of its chromosomes4 ,close to it lies its centrosomes 7,fig4 #ce1 ce71 and there is thus formed what is known as the male pronucleus 7,fig4 #ce-dj1 mn74 ,the remains of the egg nucleus1 after having discharged the polar cells1 form the female nucleus 7,fig4 #dj1 fn74 ,the chromatin material1 in both the male and female pronucleus1 soon breaks up into a network in which it is no longer possible to see that each contains two chromosomes 7,fig4 #da74 ,now the centrosome1 which is beside the male pronucleus1 shows signs of activity4 ,it becomes surrounded by prominent rays to form an aster 7,fig4 #da1 ce71 and then it begins to move toward the female pronucleus1 apparently dragging the male pronucleus after it4 ,in this way the centrosome approaches the female pronucleus1 and thus finally the two nucleii are brought into close proximity4 ,meantime the chromatin material in each has once more broken up into short threads or chromosomes1 and once more we find that each of the nucleii contains two of these bodies 7,fig4 #db74 ,in the subsequent figures the chromosomes of the male nucleus are lightly shaded1 while those of the female are black in order to distinguish them4 ,as these two nucleii finally come together their membranes disappear1 and the chromatic material comes to lie freely in the egg1 the male and female chromosomes1 side by side1 but distinct forming the segmentation nucleus4 ,the egg plainly now contains once more the number of chromosomes normal for the cells of the animal1 but half of them have been derived from each parent4 ,it is very suggestive to find further that the chromosomes in this fertilized egg do not fuse with each other1 but remain quite distinct1 so that it can be seen that the new nucleus contains chromosomes derived from each parent 7,fig4 #db74 ,nor does there appear to be1 in the future history of this egg1 any actual fusion of the chromatic material1 the male and female chromosomes perhaps always remaining distinct4 ,illustration3 ,,fig4 #da4--,the chromosomes in the male and female pronucleii have resolved into a network4 ,the male centrosome begins to show signs of activity4 ,illustration3 ,,fig4 #db4--,the centrosome has divided1 and the two pronucleii have been brought together4 ,the network in each nucleus has again resolved itself into two chromosomes which are now brought together near the centre of the egg but do not fuse2 mcr1 represents the chromosomes from the male nucleus2 fcr1 the chromosomes from the female nucleus4 ,illustration3 ,,fig4 #dc4--;,an equatorial plate is formed and each chromosome has split into two halves by longitudinal division4 ,illustration3 ,,fig4 #dd4--,the halves of the chromosomes have separated to form two nucleii1 each with male and female chromosomes4 ,the egg has divided into two cells4 ,while this mixture of chromosomes has been taking place the centrosome has divided into two parts1 each of which becomes surrounded by an aster and travels to opposite ends of the nucleus 7,fig4 #db74 ,there now follows a division of the nucleus exactly similar to that which occurs in the normal cell division already described in ,figs4 #bh-cd4 ,each of the chromosomes splits lengthwise 7,fig4 #dc71 and one half of each then travels toward each centrosome to form a new nucleus 7,fig4 #dd74 ,since each of the four chromosomes thus splits1 it follows that each of the two daughter nucleii will1 of course1 contain four chromosomes2 two of which have been derived from the male and two from the female parent4 ,from now the divisions of the egg follow rapidly by the normal process of cell division until from this one egg cell there are eventually derived hundreds of thousands of cells which are gradually moulded into the adult4 ,all of these cells will1 of course1 contain four chromosomes2 and1 what is more important1 half of the chromosomes will have been derived directly from the male and half from the female parent4 ,even into adult life1 therefore1 the cells of the animal probably contain chromatin derived by direct descent from each of its parents4 ,the ,significance of ,fertilization4--,from this process of fertilization a number of conclusions1 highly important for our purpose1 can be drawn4 ,in the first place1 it is evident that the chromosomes form the part of the cell which contain the hereditary traits handed down from parent to child4 ,this follows from the fact that the chromosomes are the only part of the cell which1 in the fertilized egg1 is derived from both parents4 ,now the offspring can certainly inherit from each parent1 and hence the hereditary traits must be associated with some part of the cell which is derived from both4 ,but the egg substance is derived from the mother alone2 the centrosome1 at least in some cases and perhaps in all1 is derived only from the father1 while the chromosomes are derived from both parents4 ,hence it follows that the hereditary traits must be particularly associated with the chromosomes4 ,with this understanding we can1 at least1 in part understand the purpose of fertilization4 ,as we shall see later1 it is very necessary in the building of the living machine for each individual to inherit characters from more than one individual4 ,this is necessary to produce the numerous variations which contribute to the construction of the machine4 ,for this purpose there has been developed the process of sexual union of reproductive cells1 which introduces into the offspring chromatic material from two parents4 ,but if the two reproductive cells should unite at once the number of chromosomes would be doubled in each generation1 and hence be constantly increasing4 ,to prevent this the polar cells are cast out1 which reduces the amount of chromatic material4 ,the union of the two pronucleii is plainly to produce a nucleus which shall contain chromosomes1 and hence hereditary traits from each parent and the subsequent splitting of these chromosomes and the separation of the two halves into daughter nucleii insures that all the nucleii1 and hence all cells of the adult1 shall possess hereditary traits derived from both parents4 ,thus it comes that1 even in the adult1 every body cell is made up of chromosomes from each parent1 and may hence inherit characters from each4 ,the cell of an animal thus consists of three somewhat distinct but active parts--the cell substance1 the chromosomes1 and the centrosome4 ,of these the cell substance appears to be handed down from the mother2 the centrosome comes1 at least in some cases1 from the father1 and the chromosomes from both parents4 ,it is not yet certain1 however1 whether the centrosome is a constant part of the cell4 ,in some cells it cannot yet be found1 and there are some reasons for believing that it may be formed out of other parts of the cell4 ,the nucleus is always a direct descendant from the nucleus of pre-existing cells1 so that there is an absolute continuity of descent between the nucleii of the cells of an individual and those of its antecedents back for numberless generations4 ,it is not certain that there is any such continuity of descent in the case of the centrosomes2 for1 while in the process of fertilization the centrosome is handed down from parent to child1 there are some reasons for believing that it may disappear in subsequent cells1 and later be redeveloped out of other parts4 ,the only part of the cell in which complete continuity from parent to child is demonstrated1 is the nucleus and particularly the chromosomes4 ,all of these facts simply emphasize the importance of the chromosomes1 and tell us that these bodies must be regarded as containing the most important features of the cell which constitute its individuality4 ,what is ,protoplasm8--,enough has now been given of disclosures of the modern microscope to show that our old friend ,protoplasm has assumed an entirely new guise1 if indeed it has not disappeared altogether4 ,these simplest life processes are so marvelous and involve the action of such an intricate mass of machinery that we can no longer retain our earlier notion of protoplasm as the physical basis of life4 ,there can be no life without the properties of assimilation1 growth1 and reproduction2 and1 so far as we know1 these properties are found only in that combination of bodies which we call the cell1 with its mixture of harmoniously acting parts4 ,life1 at least the life of a cell1 is then not the property of a chemical compound protoplasm1 but is the result of the activities of a machine4 ,indeed1 we are now at a loss to know how we can retain the term protoplasm4 ,as originally used it meant the contents of the cell1 and the significance in the term was in the conception of protoplasm as a somewhat homogeneous chemical compound uniform in all types of life4 ,but we now see that this cell contains not a single substance1 but a large number1 including solids1 jelly masses1 and liquids1 each of which has its own chemical composition4 ,the number of chemical compounds existing in the material formerly called protoplasm no one knows1 but we do know that they are many1 and that the different substances are combined to form a physical structure4 ,which of these various bodies shall we continue to call protoplasm8 ,shall it be the linin1 or the liquids1 or the microsomes1 or the chromatin threads1 or the centrosomes8 ,which of these is the actual physical basis of life8 ,from the description of cell life which we have given1 it will be evident that no one of them is a material upon which our chemical biologists can longer found a chemical theory of life4 ,that chemical theory of life1 as we have seen1 was founded upon the conception that the primitive life substance is a definite chemical compound4 ,no such compound has been discovered1 and these disclosures of the microscope of the last few years have been such as to lead us to abandon hope of ever discovering such a compound4 ,it is apparently impossible to reduce life to any simpler basis than this combination of bodies which make up what was formerly called protoplasm4 ,the term protoplasm is still in use with different meanings as used by different writers4 ,sometimes it is used to refer to the entire contents of the cell2 sometimes to the cell substance only outside the nucleus4 ,plainly1 it is not the protoplasm of earlier years4 ,with this conclusion one of our fundamental questions has been answered4 ,we found in our first chapter that the general activities of animals and plants are easily reduced to the action of a machine1 provided we had the fundamental vital powers residing in the parts of that machine4 ,we then asked whether these fundamental properties were themselves those of a chemical compound or whether they were to be reduced to the action of still smaller machines4 ,the first answer which biologists gave to this question was that assimilation1 growth1 and reproduction were the simple properties of a complex chemical compound4 ,this answer was certainly incorrect4 ,life activities are exhibited by no chemical compound1 but1 so far as we know1 only by the machine called the cell4 ,thus it is that we are again reduced to the problem of understanding the action of a machine4 ,it may be well to pause here a moment to notice that this position very greatly increases the difficulties in the way of a solution of the life problem4 ,if the physical basis of life had proved to be a chemical compound1 the problem of its origin would have been a chemical one4 ,chemical forces exist in nature1 and these forces are sufficient to explain the formation of any kind of chemical compound4 ,the problem of the origin of the life substance would then have been simply to account for certain conditions which resulted in such chemical combination as would give rise to this physical basis of life4 ,but now that the simplest substance manifesting the phenomena of life is found to be a machine1 we can no longer find in chemical forces efficient causes for its formation4 ,chemical forces and chemical affinity can explain chemical compounds of any degree of complexity1 but they cannot explain the formation of machines4 ,machines are the result of forces of an entirely different nature4 ,man can manufacture machines by taking chemical compounds and putting them together into such relations that their interaction will give certain results4 ,bits of iron and steel1 for instance1 are put together to form a locomotive1 but the action of the locomotive depends1 not upon the chemical forces which made the steel1 but upon the relation of the bits of steel to each other in the machine4 ,so far as we have had any experience1 machines have been built under the guidance of intelligence which adapts the parts to each other4 ,when therefore we find that the simplest life substance is a machine1 we are forced to ask what forces exist in nature which can in a similar way build machines by the adjustment of parts to each other4 ,but this topic belongs to the second part of our subject1 and must be for the present postponed4 ,reaction against the ,cell ,doctrine4--,as the knowledge of cells which we have outlined was slowly acquired1 the conception of the cell passed through various modifications4 ,at first the cell wall was looked upon as the fundamental part1 but this idea soon gave place to the belief that it was the protoplasm that was alive4 ,under the influence of this thought the cell doctrine developed into something like the following3 ,the cell is simply a bit of protoplasm and is the unit of living matter4 ,the bodies of all larger animals and plants are made up of great numbers of these units acting together1 and the activities of the entire organism are simply the sum of the activities of its cells4 ,the organism is thus simply the sum of the cells which compose it1 and its activities the sum of the activities of the individual cells4 ,as more facts were disclosed the idea changed slightly4 ,the importance of the nucleus became more and more forcibly impressed upon microscopists1 and this body came after a little into such prominence as to hide from view the more familiar protoplasm4 ,the marvellous activities of the nucleus soon caused it to be regarded as the important part of the cell1 while all the rest was secondary4 ,the cell was now thought of as a bit of nuclear matter surrounded by secondary parts4 ,the marvellous activities of the nucleus1 and above all1 the fact that the nucleus alone is handed down from one generation to the next in reproduction1 all attested to its great importance and to the secondary importance of the rest of the cell4 ,this was the most extreme position of the cell doctrine4 ,the cell was the unit of living action1 and the higher animal or plant simply a colony of such units4 ,an animal was simply an association together for mutual advantage of independent units1 just as a city is an association of independent individuals4 ,the organization of the animals was simply the result of the combination of many independent units4 ,there was no activity of the organism as a whole1 but only of its independent parts4 ,cell life was superior to organized life4 ,just as1 in a city1 the city government is a name given to the combined action of the individuals1 so are the actions of organisms simply the combined action of their individual cells4 ,against such an extreme position there has been in recent years a decided reaction1 and to-day it is becoming more and more evident that such a position cannot be maintained4 ,in the first place1 it is becoming evident that the cell substance is not to be entirely obliterated by the importance of the nucleus4 ,that the nucleus is a most important vital centre is clear enough1 but it is equally clear that nucleus and cell substance must be together to constitute the life substance4 ,the complicated structure of the cell substance1 the decided activity shown by its fibres in the process of cell division1 clearly enough indicate that it is a part of the cell which can not be neglected in the study of the life substance4 ,again the discovery of the centrosome as a distinct morphological element has still further added to the complexity of the life substance1 and proved that neither nucleus nor cell substance can be regarded as the cell or as constituting life4 ,it is true that we may not yet know the source of this centrosome4 ,we do not know whether it is handed down from generation to generation like the nucleus1 or whether it can be made anew out of the cell substance in the life of an ordinary cell4 ,but this is not material to its recognition as an organ of importance in the cell activity4 ,thus the cell proves itself not to2 be a bit of nuclear matter surrounded by secondary parts1 but a community of several perhaps equally important interrelated members4 ,another series of observations weakened the cell doctrine in an entirely different direction4 ,it had been assumed that the body of the multicellular animal or plant was made of independent units4 ,microscopists of a few years ago began to suggest that the cells are in reality not separated from each other1 but are all connected by protoplasmic fibres4 ,in quite a number of different kinds of tissue it has been determined that fine threads of protoplasmic material lead from one cell to another in such a way that the cells are in vital connection4 ,the claim has been made that there is thus a protoplasmic connection between all the cells of the body of the animal1 and that thus the animal or plant1 instead of consisting of a large number of separate independent cells1 consists of one great mass of living matter which is aggregated into little centres1 each commonly holding a nucleus4 ,such a conclusion is not yet demonstrated1 nor is its significance very clear should it prove to be a fact2 but it is plain that such suggestions quite decidedly modify the conception of the body as a community of independent cells4 ,there is yet another line of thought which is weakening this early conception of the cell doctrine4 ,there is a growing conviction that the view of the organism1 simply as the sum of the activities of the individual cells1 is not a correct understanding of it4 ,according to this extreme position1 a living thing can have no organization until it appears as the result of cell multiplication4 ,to take a concrete case1 the egg of a starfish can not possess any organization corresponding to the starfish4 ,the egg is a single cell1 and the starfish a community of cells4 ,the egg can1 therefore1 no more contain the organization of a starfish than a hunter in the backwoods can contain within himself the organization of a great metropolis4 ,the descendants of individuals like the hunter may unite to form a city1 and the descendants of the egg cell may1 by combining1 give rise to the starfish4 ,but neither can the man contain within himself the organization of the city1 nor the egg that of the starfish4 ,it is1 perhaps1 true that such an extreme position of the cell doctrine has not been held by any one1 but thoughts very closely approximating to this view have been held by the leading advocates of the cell doctrine1 and have beyond question been the inspiration of the development of that doctrine4 ,but certainly no such conception of the significance of cell structure would longer be held4 ,in spite of the fact that the egg is a single cell1 it is impossible to avoid the belief that in some way it contains the starfish4 ,we need not1 of course1 think of it as containing the structure of a starfish1 but we are forced to conclude that in some way its structure is such that it contains the starfish potentially4 ,the relation of its parts and the forces therein are such that1 when placed under proper conditions1 it develops into a starfish4 ,another egg placed under identical conditions will develop into a sea urchin1 and another into an oyster4 ,if these three eggs have the power of developing into three different animals under identical conditions1 it is evident that they must have corresponding differences in spite of the fact that each is a single cell4 ,each must in some way contain its corresponding adult4 ,in other words1 the organization must be within the cells1 and hence not simply produced by the associations of cells4 ,over this subject there has been a deal of puzzling and not a little experimentation4 ,the presence of some sort of organization in the egg is clear--but what is meant by this statement is not quite so clear4 ,is this adult organization in the whole egg or only in its nucleus1 and especially in the chromosomes which1 as we have seen1 contain the hereditary traits8 ,when the egg begins to divide does each of the first two cells still contain potentially the organization of the whole adult1 or only one half of it8 ,is the development of the egg simply the unfolding of some structure already present2 or is the structure constantly developing into more and more complicated conditions owing to the bringing of its parts into new relations8 ,to answer these questions experimenters have been engaged in dividing developing eggs into pieces to determine what powers are still possessed by the fragments4 ,the results of such experiments are as yet rather conflicting1 but it is evident enough from them that we can no longer look upon the egg cell as a simple undifferentiated cell4 ,in some way it already contains the characters of the adult1 and when we remember that the characters of the adult which are to be developed from the egg are already determined1 even to many minute details--such1 for instance1 as the inheritance of a congenital mark--it becomes evident that the egg is a body of extraordinary complexity4 ,and yet the egg is nothing more than a single cell agreeing with other cells in all its general characters4 ,it is clear1 then1 that we must look upon organization as something superior to cells and something existing within them1 or at least within the egg cell1 and controlling its development4 ,we are forced to believe1 further1 that there may be as important differences between two cells as there are between two adult animals or plants4 ,in some way there must be concealed within the two cells which constitute the egg of the starfish and the man differences which correspond to the differences between the starfish and the man4 ,organization1 in other words1 is superior to cell structure1 and the cell itself is an organization of smaller units4 ,as the result of these various considerations there has been1 in recent years1 something of a reaction against the cell doctrine as formerly held4 ,while the study of cells is still regarded as the key to the interpretation of life phenomena1 biologists are seeing more and more clearly that they must look deeper than simple cell structure for their explanation of the life processes4 ,while the study of cells has thrown an immense amount of light upon life1 we seem hardly nearer the centre of the problem than we were before the beginning of the series of discoveries inaugurated by the formulation of the doctrine of protoplasm4 ,fundamental ,vital ,activities as ,located in ,cells4--,we are now in position to ask whether our knowledge of cells has aided us in finding an explanation of the fundamental vital actions to which1 as we have seen1 life processes are to be reduced4 ,the four properties of irritability1 contractibility1 assimilation1 and reproduction1 belong to these vital units--the cells1 and it is these properties which we are trying to trace to their source as a foundation of vital activity4 ,we may first ask whether we have any facts which indicate that any special parts of the cell are associated with any of these fundamental activities4 ,the first fact that stands out clearly is that the nucleus is connected most intimately with the process of reproduction and especially with heredity4 ,this has long been believed1 but has now been clearly demonstrated by the experiments of cutting into fragments the cell bodies of unicellular animals4 ,as already noticed1 those pieces which possess a nucleus are able to continue their life and reproduce themselves1 while those without a nucleus are incapable of reproduction4 ,with greater force still is the fact shown by the process of fertilization of the egg4 ,the egg is very large and the male reproductive cell is very small1 and the amount of material which the offspring derives from its mother is very great compared with that which it derives from its father4 ,but the child inherits equally from father and mother1 and hence we must find the hereditary traits handed down in some element which the offspring obtains equally from father and mother4 ,as we have seen 7,figs4 #cd-dd71 the only element which answers this demand is the nucleus1 and more particularly the chromosomes of the nucleus4 ,clearly enough1 then1 we must look upon the nucleus as the special agent in reproduction of cells4 ,again1 we have apparently conclusive evidence that the nucleus controls that part of the assimilative process which we have spoken of as the constructive processes4 ,the metabolic processes of life are both constructive and destructive4 ,by the former1 the material taken into the cell in the form of food is built up into cell tissue1 such as linin1 microsomes1 etc41 and1 by the latter1 these products are to a greater or less extent broken to pieces again to liberate their energy1 and thus give rise to the activities of the cell4 ,if the destructive processes were to go on alone the organism might continue to manifest its life activities for a time until it had exhausted the products stored up in its body for such purposes1 but it would die from the lack of more material for destruction4 ,life is not complete without both processes4 ,now1 in the life of the cell we may apparently attribute the destructive processes to the cell substance and the constructive processes to the nucleus4 ,in a cell which has been cut into fragments those pieces without a nucleus continue to show the ordinary activities of life for a time1 but they do not live very long 7,fig4 #be74 ,the fragment is unable to assimilate its food sufficiently to build up more material4 ,so long as it still retains within itself a sufficiency of already formed tissue for its destructive metabolism1 it can continue to move around actively and behave like a complete cell1 but eventually it dies from starvation4 ,on the other hand1 those fragments which retain a piece of the nucleus1 even though they have only a small portion of the cell substance1 feed1 assimilate1 and grow2 in other words1 they carry on not only the destructive but also the constructive changes4 ,plainly1 this means that the nucleus controls the constructive processes1 although it does not necessarily mean that the cell substance has no share in these constructive processes4 ,without the nucleus the cell is unable to perform those processes1 while it is able to carry on the destructive processes readily enough4 ,the nucleus controls1 though it may not entirely carry on1 the constructive metabolism4 ,it is equally clear that the cell substance is the seat of most of the destructive processes which constitute vital action4 ,the cell substance is irritable1 and is endowed with the power of contractility4 ,cell fragments without nucleii are sensitive enough1 and can move around as readily as normal cells4 ,moreover1 the various fibres which surround the centrosomes in cell division and whose contractions and expansions1 as we have seen1 pull the chromosomes apart in cell division1 are parts of the cell substance4 ,all of these are the results of destructive metabolism1 and we must1 therefore1 conclude that destructive processes are seated in the cell substance4 ,the centrosome is too problematical as yet for much comment4 ,it appears to be a piece of the machinery for bringing about cell division1 but beyond this it is not safe to make any statements4 ,in brief1 then1 the cell body is a machine for carrying on destructive chemical changes1 and liberating from the compounds thus broken to pieces their inclosed energy1 which is at once converted into motion or heat or some other form of active energy4 ,this chemical destruction is1 however1 possible only after the chemical compounds have become a part of the cell4 ,the cell1 therefore1 possesses a nucleus which has the power of enabling it to assimilate its food--that is1 to convert it into its own substance4 ,the nucleus further contains a marvellous material--chromatin--which in someway exercises a controlling influence in its life and is handed down from one generation to another by continuous descent4 ,lastly1 the cell has the centrosome1 which brings about cell division in such a manner that this chromatin material is divided equally among the subsequent descendants1 and thus insures that the daughter cells shall all be equivalent to each other and to the mother cell4 ,we must therefore look upon the organic cell as a little engine with admirably adapted parts4 ,within this engine chemical activity is excited4 ,the fuel supplied to the engine is combined by chemical forces with the oxygen of the air4 ,the vigour of the oxidation is partly dependent upon temperature1 just as it is in any other oxidation process1 and is of course dependent upon the presence of fuel to be oxidized1 and air to furnish the oxygen4 ,unless the fuel is supplied and the air has free access to it1 the machine stops1 the cell dies4 ,the energy liberated in this machine is converted into motion or some other form4 ,we do not indeed understand the construction of the machine well enough to explain the exact mechanism by which this conversion takes place1 but that there is such a mechanism can not be doubted1 and the structure of the cell is certainly complex enough to give plenty of room for it4 ,the irritability of the cell is easily understood2 for1 since it is made of very unstable chemical compounds1 any slight disturbance or stimulation on one part will tend to upset its chemical stability and produce reaction2 and this is what is meant by irritability4 ,or1 again1 we may look upon the cell as a little chemical laboratory1 where chemical changes are constantly occurring4 ,these changes we do not indeed understand1 but they are undoubtedly chemical changes4 ,the result is that some compounds are pulled to pieces and part of the fragments liberated or excreted1 while other parts are retained and built into other more complex compounds4 ,the compounds thus manufactured are retained in the cell body1 and it grows in bulk4 ,this continues until the cell becomes too big1 and then it divides4 ,if a machine is broken it ceases to carry on its proper duties1 and if the parts are badly broken it is ruined4 ,so with the cell4 ,if it is broken by any means1 mechanical1 thermal1 or otherwise1 it ceases to run--we say it dies4 ,it has within itself great power of repairing injury1 and therefore it does not cease to act until the injury is so great as to be beyond repair4 ,thus it only stops its motion when the machinery has become so badly injured as to be beyond hope of repair1 and hence the cell1 after once ceasing its action1 can never resume it again4 ,there are1 of course1 other functions of living things besides the few simple ones which we have considered4 ,but these are the fundamental ones2 and if we can reduce them to an intelligible explanation1 we may feel that we have really grasped the essence of life4 ,if we understand how the cell can move and grow and reproduce itself1 we may rest assured that the other phenomena of life follow as a natural consequence4 ,if1 therefore1 we have obtained an understanding of these fundamental vital phenomena1 we have accomplished our object of comprehending the life phenomena in our chemical and mechanical laws4 ,but have we thus reduced these fundamental phenomena to an intelligible explanation8 ,it must be acknowledged that we have not4 ,we have reduced them to the action of chemical forces acting in a machine4 ,but the machine itself is unintelligible4 ,the organic cell is no more intelligible to us than is the body as a whole4 ,the chemical understanding which we thought we had a few years ago in protoplasm has failed us1 and nothing has taken its place ,we have no conception of what may be the primitive life substance4 ,all we can say is that this most marvellous of all natural phenomena occurs only within that peculiar piece of machinery which we call the cell1 and that it is the result of the action of physical forces in that machine4 ,how the machine acts1 or even the structure of the machine1 we are as far from understanding as we were fifty years ago4 ,the solution has retreated before us even faster than we have advanced toward it4 ,summary4--,we may now notice in a brief summary the position which we have reached4 ,in our attempt to explain the living organism on the principle of the machine1 we are very successful so far as secondary problems are concerned4 ,digestion1 circulation1 respiration1 and motion are readily solved upon chemical and mechanical principles4 ,even the phenomena of the nervous system are1 in a measure1 capable of comprehension within a mechanical formula1 leaving out of account the purely mental phenomena which certainly have not been touched by the investigation4 ,all of these phenomena are reducible to a few simple fundamental activities1 and these fundamental activities we find manifested by simple bits of living matter unincumbered by the complicated machinery of organisms4 ,with the few fundamental properties of these bits of organic matter we can construct the complicated life of the higher organism4 ,when we come1 however1 to study these simple bits of matter1 they prove to be anything but simple bits of matter4 ,they1 too1 are pieces of complicated mechanism whose action we do not even hope to understand4 ,that their action is dependent upon their machinery is evident enough from the simple description of cell activity which we have noticed4 ,that these fundamental vital properties are to be explained as the result of chemical and mechanical forces acting through this machinery1 can not be doubted4 ,but how this occurs or what constitutes the guiding force which corresponds to the engineer of the machine1 we do not know4 ,thus our mechanical explanation of the living machine lacks a foundation4 ,we can understand tolerably well the building of the superstructure1 but the foundation stones upon which that structure is built are unintelligible to us4 ,the running of the living machine is thus only in part understood4 ,the living organism is a machine or1 it is better to say1 it is a series of machines one within the other4 ,as a whole it is a machine1 and its parts are separate machines4 ,each part is further made up of still smaller machines until we reach the realm of the microscope4 ,here still we find the same story4 ,even the parts formerly called units1 prove to be machines1 and when we recognize the complexity of these cells and their marvellous activities1 we are ready to believe that we may find still further machines within4 ,and thus vital activity is reduced to a complex of machines1 all acting in harmony with each other to produce together the one result--life4 ,,part ,,ii4 ,,the ,,building ,,of ,,the ,,living ,,machine4 99 99 99 99 99 ,,chapter ,,iii4 ,,the ,,factors ,,concerned ,,in ,,the ,,building ,,of ,,the ,,living ,,machine4 ,having now outlined the results of our study into the mechanism of the living machine1 we turn our attention next to the more difficult problem of the method by which this machine was built4 ,from the facts which we have been considering in the last two chapters it is evident that the problem we have before us is a mechanical rather than a chemical one4 ,of course1 chemical forces lie at the bottom of vital activity1 and we must look upon the force of chemical affinity as the fundamental power to which the problems must be referred4 ,but a chemical explanation will evidently not suffice for our purpose2 for we have absolutely no reason for believing that the phenomena of life can occur as the results of the chemical properties of any compound1 however complex4 ,the simplest known form of matter which manifests life is a machine1 and the problem of the origin of life must be of the origin of that machine4 ,are there any forces in nature which are of a sort as to enable us to use them to explain the building of machines8 ,plants and animals are the only machines which nature has produced4 ,they are the only instances in nature of a structure built with its parts harmoniously adjusted to each other to the performance of certain ends4 ,all other machines with which we are acquainted were made by man1 and in making them intelligence came in to adapt the parts to each other4 ,but in the living organism is a similarly adapted machine made by natural means rather than artificial4 ,how were they built8 ,does nature1 apart from human intelligence1 possess forces which can achieve such results8 ,here again we must attack the problem from what seems to be the wrong end4 ,apparently it would be simpler to discover the method of the manufacture of the simplest machine rather than the more complex ones4 ,but this has proved contrary to the fact4 ,perhaps the chief reason is that the simplest living machine is the cell whose study must always involve the use of the microscope1 and for this reason is more difficult4 ,perhaps it is because the problem is really a more difficult one than to explain the building of the more complex machines out of the simpler ones4 ,at all events1 the last fifty years have told us much of the method of the building of the complex machines out of the simpler ones1 while we have as yet not even a hint as to the solution of the building of the simplest machine from the inanimate world4 ,our attention must1 therefore1 be first directed to the method by which nature has constructed the complex machines which we find filling the world to-day in the form of animals and plants4 ,history of the ,living ,machine4--,in the first place1 we must notice that these machines have not been fashioned suddenly or rapidly1 but have been the result of a very slow growth4 ,they have had a history extending very far back into the past for a period of years which we can only indefinitely estimate1 but certainly reaching into the millions4 ,as we look over this past history in the light of our present knowledge we see that whatever have been the forces which have been concerned in the construction of these machines they have acted very slowly4 ,it has taken centuries1 and1 indeed1 thousands of years1 to take the successive steps which have been necessary in this construction4 ,secondly1 we notice that the machines have been built up step by step1 one feature being added to another with the slowly progressing ages4 ,thirdly1 we notice that in one respect this construction of the living machine by nature's processes has been different from our ordinary method of building machines4 ,our method of building puts the parts gradually into place in such a way that until the machine is finished it is incapable of performing its functions4 ,the half-built engine is as useless and as powerless as so much crude iron4 ,its power of action only appears after the last part is fitted into place and the machine finished4 ,but nature's process in machine building is different4 ,every step in the process1 so far as we can trace it at least1 has produced a complete machine4 ,so far back as we can follow this history we find that at every point the machine was so complete as to be always endowed with motion and life activity4 ,nature's method has been to take simpler types of machines and slowly change them into more complicated ones without at any moment impairing their vigour4 ,it is something as if the steam engine of ,watt should be slowly changed by adding piece after piece until there was finally produced the modern quadruple expansion engine1 but all this change being made upon the original engine without once stopping its motion4 ,illustration3 ,,fig4 #de4 ,a group of cells resulting from division1 representing the first step in machine making4 ,this gradual construction of the living machines has been called ,organic ,evolution1 or the ,theory of ,descent4 ,it will be necessary for us1 in order to comprehend the problem which we have before us1 to briefly outline the course of this evolution4 ,our starting point in this history must be the cell1 for such is the earliest and simplest form of living thing of which we have any trace4 ,this cell is1 of course1 already a machine1 and we must presently return to the problem of its origin4 ,at present we will assume this cell as a starting point endowed with its fundamental vital powers4 ,it was sensitive1 it could feel1 grow1 and reproduce itself4 ,from such a simple machine1 thus endowed1 the history has been something as follows3 ,in reproducing itself this machine1 as we have already seen1 simply divided itself into two halves1 each like the other4 ,at first all the parts thus arising separated from each other and remained independent4 ,but so long as this habit continued there could be little advance4 ,after a time some of the cells failed to separate after division1 but remained clinging together 7,fig4 #de74 ,the cells of such a mass must have been at first all alike2 but1 after a little1 differences began to appear among them4 ,those on the outside of the mass were differently affected by their surroundings from those in the interior1 and soon the cells began to share among themselves the different duties of life4 ,the cells on the outside were better situated for protection and capturing food1 while those on the inside could not readily seize food for themselves1 and took upon themselves the duty of digesting the food which was handed to them by the outer cells4 ,each of these sets of cells could now carry on its own special duties to better advantage1 since it was freed from other duties1 and thus the whole mass of cells was better served than when each cell tried to do everything for itself4 ,this was the first step in the building of the machine out of the active cells 7,fig4 #df74 ,from such a starting point the subsequent history has been ever based upon the same principle4 ,there has been a constant separation of the different functions of life among groups of cells1 and as the history went on this division of labor among the different parts became greater and greater4 ,group after group of cells were set apart for one special duty after another1 and the result was a larger and ever more complicated mass of cells1 with a greater and greater differentiation among them4 ,in this building of the machine there was no time when the machine was not active4 ,at all points the machine was alive and functional1 but each step made the total function of the machine a little more accurately performed1 and hence raised somewhat the totality of life powers4 ,this parcelling out of the different duties of life to groups of cells continued age after age1 each step being a little advance over the last1 until the result has been the living machine as we know it in its highest form1 with its numerous organs1 all interrelated in such a way as to form a harmoniously acting whole4 ,illustration3 ,,fig4 #df4 ,a later step in machine building in which the outer cells have acquired different form and function from the inner cells3 ec1 the outer cells1 whose duties are protective2 en1 the inner cells engaged in digesting food4 ,but a second principle in this growth of the machine was needed to produce the variety which is found in nature4 ,as the different cells in the multicellular mass became associated into groups for different duties1 the method of such division of labor was not alike in all machines4 ,a city in ,china and one in ,america are alike made up of individuals1 and the fundamental needs of the ,chinaman and the ,american are alike4 ,but differences in industrial and political conditions have produced different combinations and associations1 so that ,pekin is wonderfully unlike ,new ,york4 ,so in these early developing machines1 quite a variety of method of organization was adopted by the different groups4 ,now as soon as any special type of organization was adopted by any animal or plant1 the principle of heredity transmitted the same kind of organization to its descendants1 and there thus arose lines of descent differing from each other1 each line having its own method of organization4 ,as we follow the history of each line the same thing is repeated4 ,we find that the representatives of each line again separate into groups1 each of which has acquired some new type of organization1 and there has thus been a constant divergence of these lines of descent in an indefinite number of directions4 ,the members of the different lines of descent all show a fundamental likeness with each other since they retain the fundamental characters of their common ancestor1 but they show also the differences which they have themselves acquired4 ,and thus the process is repeated over and over again4 ,this history of the growth of these different machines has thus been one of divergence from common centres1 and is to be diagrammatically expressed after the fashion of a branching tree4 ,the end of each branch represents the highest state of perfection to which each line has been carried4 ,one other point in this history must be noted4 ,as the development of the complication of the machine progressed the possibility of further progress has been constantly narrowed4 ,when the history of these machines began as a simple mass of cells1 there was a possibility of an almost endless variety of methods of organization4 ,but as a distinct type of organization was adopted by one and another line of descendants all subsequent productions were limited through the law of heredity to the general line of organization adopted by their ancestors4 ,with each age the further growth of such machines must consist in the further development in the perfection of its parts1 and not in the adoption of any new system of organization4 ,hence it is that the history of the living machine has shown a tendency toward development along a few well-marked lines1 and although this complication becomes greater1 we still see the same fundamental scheme of organization running through the whole4 ,as the ages have progressed the machines have become more perfect in the adjustment of their parts1 i4e41 they have become more perfect machines1 but the history has been simply that of perfecting the early machines rather than the production of new types4 ,evidence for this ,history4--,as just outlined1 we see that the living machines have been gradually brought into their present condition by a process which has been called organic evolution4 ,but we must pause for a moment to ask what is our evidence that such has been the history of the living machine4 ,the whole possibility of understanding living nature depends upon our accepting this history and finding an explanation of it4 ,at the outset we have the question of fact1 and we must notice the grounds upon which we stand in assuming this history to be as outlined4 ,this problem is the one which has occupied such a prominent place in the scientific world during the last forty years1 and which has contributed so largely toward making modern biology such a different subject from the earlier studies of natural history4 ,it is simply the evidence for organic evolution1 or the theory of descent4 ,the subject has for forty years been thoroughly sifted and tested by every conceivable sort of test4 ,as a result of the interest in the question there has been disclosed an immense mass of evidence1 relevant and irrelevant4 ,as the evidence has accumulated it has become more and more evident that the evolution theory must be recognized as the only one which is in accord with the facts1 and the outcome has been a practical unanimity among thinkers that the theory of descent must be the foundation of our further study4 ,the evidence which has forced this conclusion upon scientists we must stop for a moment to consider1 since it bears very directly upon the subject we are studying4 ,historical4--,the first source of evidence is naturally a historical one4 ,this long history of the construction of the living machine has left its record in the rocks which form the earth's surface4 ,during this long period the rocks of the earth's crust have been deposited1 and in these rocks have been left samples of many of the steps in this history of machine building4 ,the history can be traced by the study of these samples just as the history of any machine might be traced from a study of the models in a patent office4 ,one might very easily trace1 with most strict accuracy and minute detail1 the history of the printing machine from the models which are preserved in the patent offices and elsewhere4 ,so is it with the history of the living machine4 ,to be sure1 the history is rather incomplete and at times difficult to read4 ,many a period in the development has left no samples for our inspection and must be interpreted in our history between what went before and what comes after4 ,many of the machines1 especially the early ones1 were made of such fragile material that they could not be preserved in the rocks4 ,in many a case1 too1 the rocks in which the specimens were deposited have been subjected to such a variety of heatings and pressures1 that they have been twisted out of shape and even crushed out of recognizable form4 ,but in spite of this the record is showing itself more complete each year4 ,our paleontologists are opening layer after layer of these rocks1 and thus examining each year new pages in nature's history4 ,the more recent epochs in the history have been already read with almost historic accuracy4 ,from them we have learned in great detail how the finishing touches were given to these machines1 and are able to trace with accuracy how the somewhat more generalized forms of earlier days were changed to produce our modern animals4 ,this fossil record has given us our best knowledge of the course by which the present living world has been brought into its existing condition4 ,but its accuracy is largely confined to the recent periods4 ,of the very early history fossils tell us little or nothing4 ,all the early rocks1 which we may believe were formed during the period when the first steps in this machine building were taken1 have been so changed by heat and pressure that whatever specimens they may have originally contained have been crushed out of shape4 ,furthermore1 the earliest organisms had no hard skeletons1 and it was not until living beings had developed far enough to have hard parts that it was possible for them to leave traces of themselves in the rocks4 ,hence1 so far as concerns this earliest history1 we can get no record of it in the rocks4 ,embryological4--,but here comes in another source of evidence which helps to fill up the gap4 ,in its development every animal to-day begins as an egg4 ,this is a simple cell1 and the animal goes through a series of changes which eventually lead to the adult4 ,now these changes appear for the most part to be parallel to the changes through which the earlier forms of life passed in their development from the simple to the more complicated forms4 ,where it is possible to follow the history of the groups of animals from their fossil remains and compare it with the history of the individual animal as it progresses from the egg to the adult1 there is found a very decided parallelism4 ,this parallelism between embryology and past history has been of great service in helping us toward the history of the past4 ,at one time it was believed that it was the key which would unlock all doors1 and for a decade biologists eagerly pursued embryology with the expectation that it would solve all problems in connection with the history of animals4 ,the result has been somewhat disappointing4 ,embryology has1 it is true1 been of the utmost service in showing relationships of forms to each other1 and in thus revealing past history4 ,but while this record is a valuable one1 it is a record which has unfortunately been subject to such modifying conditions that in many cases its original meaning has been entirely obliterated and it has become worthless as a historical record4 ,these imperfections in regard to the record were early seen after the attention of biologists was seriously turned to the study of embryology1 but it was expected that it would be possible to correct them and discover the true meaning underlying the more apparent one4 ,indeed1 in many cases this has been found possible4 ,but many of the modifications are so profound as to render it impossible to untangle them and discover the true meaning4 ,as a result the biologist to-day is showing less confidence in embryology1 and is turning his attention in different directions as more promising of results in the line desired4 ,but although the teachings of embryology have failed to realize the great hopes that were placed upon them1 their assistance in the formulation of this history of the machine has been of extreme value4 ,many a bit of obscurity has been cleared up when the embryology of puzzling animals has been studied4 ,many a relationship has been made clear1 and this is simply another way of saying that a portion of this history of life has been read4 ,this aid of embryology has been particularly valuable in just that part of the history where the evidence from the study of fossils is wanting4 ,the study of fossils1 as we have seen1 gives little or no data concerning the early history of living machines2 and it is just here that embryology has proved to be of the most value4 ,it is a source of evidence that has told us of most of the steps in the progress from the single-celled animal to the multicellular organisms1 and gives us the clearest idea of the fundamental principles which have been concerned in the evolution of life and the construction of the complicated machine out of the simple bit of protoplasm4 ,in spite of its limits1 therefore1 embryology has contributed a large quota of the evidence which we have of the evolution of life4 ,anatomical4--,a third source of this history is obtained from the facts of comparative anatomy4 ,the essential feature of this subject is the fact that animals and plants show relationships4 ,this fact is one of the most patent and yet one of the most suggestive facts of biology4 ,it has been recognized from the very beginning of the study of animals and plants4 ,one cannot be even the most superficial observer without seeing that certain forms show great likeness to each other while others are much more unlike4 ,the grouping of animals and plants into orders1 genera1 and species is dependent upon this relationship4 ,if two forms are alike in everything except some slight detail1 they are commonly placed in the same genus but in different species1 while if they show a greater unlikeness they may be placed in separate genera4 ,by thus grouping together forms according to their resemblance the animal and vegetable kingdoms are classified into groups subordinate to groups4 ,the principle of relationship1 i4e41 fundamental similarity of structure1 runs through the whole animal and vegetable kingdom4 ,even the animals most unlike each other show certain points of similarity which indicates a relationship1 although of course a distant one4 ,the fact of such a relationship is too patent to demand more words1 but its significance needs to be pointed out4 ,when we speak of relationship among men we always mean historical connection4 ,two brothers are closely related because they have sprung from common parents1 while two cousins are less closely related because their common point of origin was farther back in time4 ,more widely we speak of the relationship of the ,indo-,european races1 meaning thereby that back in the history of man these races had a common point of origin4 ,we never speak of any real relation of objects unless thereby we mean to imply historical connection4 ,we are therefore justified in interpreting the manifest relationships of organisms as pointing to history4 ,particularly are we justified in this conclusion when we find that the relationships which we draw between the types of life now in existence run parallel to the history of these types as revealed to us by fossils and at the same time disclosed by the study of embryology4 ,this subject of comparative anatomy includes a consideration of what is called homology1 and perhaps a concrete example may be instructive both in illustration and as suggesting the course which nature adopts in constructing her machines4 ,we speak of a monkey's arm and a bird's wing as homologous1 although they are wonderfully different in appearance and adapted to different duties4 ,they are called homologous because they have similar parts in similar relations4 ,this can be seen in ,figs4 #dg and #dh1 where it will be seen that each has the same bones1 although in the bird's wing some of the bones have been fused together and others lost4 ,their similarity points to a relationship1 but their dissimilarity tells us that the relationship is a distant one1 and that their common point of origin must have been quite far back in history4 ,now if we follow back the history of these two kinds of appendages1 as shown to us by fossils1 we find them approaching a common point4 ,the arm can readily be traced to a walking appendage1 while the bird's wing1 by means of some interesting connecting links1 can in a similar way be traced to an appendage with its five fingers all free and used for walking4 ,fig4 #di shows one of these connecting links representing the earliest type of bird1 where the fingers and bones of the arm were still distinct1 and yet the whole formed a true wing4 ,thus we see that the common point of origin which is suggested by the likenesses between an arm and a wing is no mere imaginary one1 for the fossil record has shown us the path leading to that point of origin4 ,the whole tells us further that nature's method of producing a grasping or flying organ was here1 not to build a new organ1 but to take one that had hitherto been used for other purposes1 and by slow changes modify its form and function until it was adapted to new duties4 ,illustration3 ,,fig4 #dg4--,the arm of a monkey1 a prehensile appendage4 ,illustration3 ,,fig4 #dh4--,the arm of a bird1 a flying appendage4 ,in life covered with feathers4 ,illustration3 ,,fig4 #di4--,the arm of an ancient half-bird half-reptile animal4 ,in life covered with feathers and serving as a wing4 ,significance of these ,sources of ,history4--,the real force of these sources of evidence comes to us only when we compare them with each other4 ,they agree in a most remarkable fashion4 ,the history as disclosed by fossils and that told by embryology agree with each other1 and these are in close harmony with the history as it can be read from comparative anatomy4 ,if archologists were to find1 in different countries and entirely unconnected with each other two or more different records of a lost nation1 the belief in the actual existence of that nation would be irresistible4 ,when researches at ,nineveh1 for example1 unearth tablets which give the history of ancient nations1 and when it proves that among the nations thus mentioned are some with the same names and having the same facts of history as those mentioned in the ,bible1 it is absolutely impossible to avoid the conclusion that such a nation with such a history did actually exist4 ,two independent sources of record could not be false in regard to such a matter as this4 ,now1 our sources of evidence for this history of the living machine prove to be of exactly this kind4 ,we have three independent sources of evidence which are so entirely different from each other that there is almost no likeness between them4 ,one is written in the rocks1 one in bone and muscle1 while the third is recorded in the evanescent and changing pages of embryology and metamorphosis4 ,yet each tells the same story4 ,each tells of a history of this machine from simple forms to more complex4 ,each tells of its greater and greater differentiation of labour and structure as the periods of time passed4 ,each tells of a growing complexity and an increasing perfection of the organisms as successive periods pass4 ,each tells us of common points of origin and divergence from these points4 ,each tells us how the more complicated forms have arisen as the results of changes in and modifications of the simpler forms4 ,each shows us how the individual parts of the organisms have been enlarged or diminished or changed in shape to adapt them to new duties4 ,each1 in short1 tells the same story of the gradual construction of the living machine by slow steps and through long ages of time4 ,when these three sources of history so accurately agree with each other1 it is as impossible to disbelieve in the existence of such history as it is to disbelieve in the existence of the ancient ,hittite nation1 after its history has been told to us by two different sources of record4 ,now all this is very germane to our subject4 ,we are trying to learn how this living machine1 with its wonderful capabilities1 was built4 ,the history which we have outlined is undoubtedly the history of the building of this machine1 and the knowledge that these complicated machines have been produced as the result of slow growth is of the utmost importance to us4 ,this knowledge gives us at the very start some idea of the nature of the forces which have been at work4 ,it tells us that in searching for these forces we must look for those which have been acting constantly4 ,we must look for forces which produce their effects not by sudden additions to the complication of the machine4 ,they must be constant forces whose effect at any one time is comparatively slight1 but whose total effect is to increase the complexity of the machine4 ,they must be forces which produce new types through the modification of the old ones4 ,we must look for forces which do not adapt the machine for its future1 but only for its present need4 ,each step in the history has been a complete animal with its own fully developed powers4 ,we are not to expect to find forces which planned the perfect machine from the start1 nor forces which were engaged in constructing parts for future use4 ,each step in the building of the machine was taken for the good of the machine at the particular moment1 and the forces which we are to look for must therefore be only such as can adapt the organisms for its present needs4 ,in other words1 nothing has been produced in this machine for the purpose of being developed later into something of value1 but all parts that have been produced are of value at the time of their appearance4 ,we must1 in short1 look for forces constantly in action and always tending in the same direction of greater complexity of structure4 ,is it possible to discover these forces and comprehend their action8 ,before the modern development of evolution this question would unhesitatingly have been answered in the negative4 ,to-day1 under the influence of the descent theory1 stimulated1 in the first place1 by ,darwin1 the question will be answered by many with equal promptness in the affirmative4 ,at all events1 we have learned in the last forty years to recognize some of the factors which have been at work in the construction of this machine4 ,we must turn1 therefore1 to the consideration of these factors4 ,forces at ,work in the ,building of the ,living ,machine4--,there are three primary factors which lie at the bottom of the whole process4 ,they are-- #a4 ,reproduction1 which preserves type from generation to generation4 #b4 ,variation1 which modifies type from generation to generation4 #c4 ,heredity1 which transmits characters from generation to generation4 ,each must be considered by itself4 ,reproduction4--,reproduction is the primary factor in this process of machine building1 heredity and variation being simply phases of reproduction4 ,the living machine has developed by natural processes1 all other machines by artificial methods4 ,reproduction is the one essential point of difference between the living machine and the others which has made their construction by natural processes a possibility4 ,what1 then1 is reproduction8 ,reproduction is in all cases at the bottom simple division4 ,whether we consider the plant that multiplies by buds or the unicellular animal that simply divides into two equal parts1 or the larger animal that multiplies by eggs1 we find that in all cases the fundamental feature of the process is division4 ,in all cases the organism divides into two or more parts1 each of which becomes in time like the original4 ,moreover1 when we trace this division further we find that in all cases it is to be referred back to the division of the cell1 such as we have described in a previous chapter4 ,the egg is a single cell which has come from the parent by the division of one of the cells in the body of the parent4 ,a bud is simply a mass of cells which have all arisen from the parent cells by division4 ,the foundation of reproduction is thus in all cases cell division4 ,now1 this process of division is dependent upon the properties of the cell4 ,firstly1 it is a result of the assimilative powers of the cell1 for only through assimilation can the cell increase in size1 and only as it increases in size can it gain sustenance for cell division4 ,secondly1 it is dependent1 as we have seen1 upon the mechanism of the cell body1 and especially the nucleus and centrosome4 ,these structures regulate the cell division1 and hence the reproduction of all animals and plants4 ,we can not1 therefore1 find any explanation of reproduction until we have explained the mechanism of the cell4 ,the fundamental feature1 of nature's machine building is thus based upon the machinery of the nucleus and centrosome of the organic cell4 ,aside from the simple fact that it preserves the race1 the most important feature connected with this reproduction is its wonderful fruitfulness4 ,since it results from division1 it always tends to increase the offspring in geometrical ratio4 ,in the simplest case1 that of the unicellular animals1 the cell divides1 giving rise to two animals1 each of which divides again1 producing four1 and these again1 giving eight1 etc4 ,the rapidity of this multiplication is sometimes inconceivable4 ,it depends1 of course1 upon the interval of time between the successive divisions1 but among the lower organisms this interval is sometimes not more than half an hour1 the result of which is that a single individual could give rise in the course of twenty-four hours to sixteen million offspring4 ,this is doubtless an extreme case1 but among all the lower animals the rate is very great4 ,among larger animals the process is more complicated2 but here1 too1 there is the same tendency to geometrical progression1 although the intervals between the successive reproductions may be quite long and irregular4 ,but it is always so great that if allowed to progress unhindered at its normal rate the offspring would1 in a few years1 become so numerous as to crowd other life out of existence4 ,even the slow-breeding elephant would1 if allowed to breed unhindered for seven hundred and fifty years1 produce nineteen million offspring--a rate of increase plainly incompatible with the continued existence of other animals4 ,here1 then1 we have the foundation of nature's method of building animals and plants of the higher classes4 ,in the machinery of the cell she has a power of reproduction which produces an increase in geometrical ratio far beyond the possibility for the surface of the earth to maintain4 ,heredity4--,the offspring which arise by these processes of division are like each other1 and like the parent from which they sprung4 ,this is the essence of what is called heredity4 ,its significance in the process of machine building is evident at once4 ,it is the conserving force which preserves the forms already produced and makes it possible for each generation to build upon the structures of the earlier ones4 ,without it each generation would have to begin anew at the beginning1 and nothing could be accomplished4 ,but since this principle brings each individual to the same place where its parents stand1 and thus always builds the offspring into a machine like the parent1 it makes it possible for the successive generations to advance4 ,heredity is thus like the power of memory1 or better still1 like the invention of printing in the development of civilization4 ,it is a record of past achievements4 ,by means of printing each age is enabled to benefit by the discoveries of the previous age1 and without it the development of civilization would be impossible4 ,in the same way heredity enables each generation to benefit by the achievements of its ancestors in the process of machine building1 and thus to devote its own energies to advancement4 ,the fact of heredity is patent enough4 ,it has been always clearly recognized that the child has the characters of its parents1 and this belief is so well attested as to need no proof4 ,it is still a question as to just what characters may be inherited1 and what influences may affect the inheritance4 ,there are plenty of puzzling problems connected with heredity1 but the fact of heredity is one of the foundation stones of biological science4 ,upon it must be built all theories which look toward the explanation of the origin of the living machine4 ,this factor of heredity again we must trace back to the machinery of the cell4 ,we have seen in the previous pages evidence for the wonderful nature of the chromosomes of the cells4 ,we can not pretend to understand them1 but they must be extraordinarily complex4 ,we have seen proof that these chromosomes are probably the physical basis of heredity1 since they are the only parts of each parent which are handed down to subsequent generations4 ,with these various facts of cell division and cell fertilization in mind1 we can reach a very simple explanation of fundamental features of heredity4 ,the following is an outline of the most widely accepted view of the hereditary process4 ,recognizing that the chromosomes are the physical basis of hereditary transmission1 we can picture to ourselves the transmission of hereditary characters something as follows3 ,as we have seen1 the fertilized egg contains an equal number of chromosomes from each parent 7,fig4 #db74 ,now when this fertilized cell divides1 each of the rods splits lengthwise1 half of each entering each of the two cells arising from the cell division4 ,from this method of division of the chromosomes it follows that the daughter cells would be equivalent to each other and equivalent also to the undivided egg4 ,if the original chromosomes contained potentially all the hereditary traits handed down from parent to child1 the chromosomes of each daughter cell will contain similar hereditary traits4 ,if1 therefore1 the original fertilized egg possessed the power of developing into an adult like the parent1 each of the daughter cells should likewise possess the power of developing into a similar adult4 ,and thus each cell which arises as the result of such division should possess similar characters so long as this method of division continues4 ,but after a little in the development of the egg a differentiation among the daughter cells arises4 ,they begin to acquire different shapes and different functions4 ,this we can only believe to be the result of a differentiation in their chromatin material4 ,in the cell division the chromosomes no longer split into equivalent halves1 but some characters are portioned off to some cells and others to other cells4 ,those cells which are to carry on digestive functions when they are formed receive chromatin material which especially controls them in the performance of this digestive function1 while those which are to produce sensory organs receive a different portion of the chromatin material4 ,thus the adult individual is built up as the cells receive different portions of this hereditary substance contained in the original chromosomes4 ,the original chromosomes contained all hereditary characters1 but as development proceeds these are gradually portioned out among the daughter cells until the adult is formed4 ,from this method of division it will be seen that each cell of the adult does not contain all the characters concealed in the original chromosomes of the egg1 although each contains a part which may have been derived from each parent4 ,it is thought1 however1 that a part of the original chromatin material does not thus become differentiated1 but remains entirely unchanged as the individual is developing4 ,this chromatin material may increase in amount by assimilation1 but it remains unchanged during the entire growth of the individual4 ,it thus follows that the adult will contain1 along with its differentiated material1 a certain amount of the original physical basis of heredity which still retains its original powers4 ,this undifferentiated chromatin material originally possessed powers of producing a new individual1 and of course it still possesses these powers1 since it has remained dormant without alteration4 ,further1 it will follow that if this dormant undifferentiated chromatin should start into activity and produce a new individual1 the new individual thus produced would be identical in all characters with the one which actually did develop from the egg1 since both individuals would have come from a bit of the same chromatin4 ,the child would be like the parent4 ,this would be true no matter how much this undifferentiated material should increase in amount by assimilation1 so long as it remained unaltered in character1 and it hence follows that every individual carries around a certain amount of undifferentiated chromatin material in all respects identical with that from which he developed4 ,now whether this undifferentiated germ plasm1 as we will now call it1 is distributed all over the body1 or is collected at certain points1 is immaterial to our purpose4 ,it is certain that portions of it find their way into the reproductive organs of the animal or plant4 ,thus we see that part of the chromatin material in the egg of the first generation develops into the second generation1 while another part of it remains dormant in that second generation1 eventually becoming the chromatin of its eggs and spermatozoa4 ,thus each egg of the second generation receives chromosomes which have come directly from the first generation1 and thus it will follow that each of these eggs will have identical properties with the egg of the first generation4 ,hence if one of these new eggs develops into an adult it will produce an adult exactly like the second generation1 since it contains chromosomes which are absolutely identical with those from which the second generation sprung4 ,there is thus no difficulty in understanding why the second generation will be like the first1 and since the process is simply repeated again in the next reproduction1 the third generation will be like the second1 and so on1 generation after generation4 ,a study of the accompanying diagram will make this clear4 ,in other words1 we have here a simple understanding of at least some of the features of heredity4 ,this explanation is that some of the chromatin material or germ plasm is handed down from one generation to another1 and is stored temporarily in the nucleii of the reproductive cells4 ,during the life of the individual this germ plasm is capable of increasing in amount without changing its nature1 and it thus continues to grow and is handed down from generation to generation1 always endowed with the power of developing into a new individual under proper conditions1 and of course when it does thus give rise to new individuals they will all be alike4 ,we can thus easily understand why a child is like its parent4 ,it is not because the child can inherit directly from its parent1 but rather because both child and parent have come from the unfolding of two bits of the same germ plasm4 ,this fact of the transmission of the hereditary substance from generation to generation is known as the theory of the continuity of germ plasm4 ,such appears to be1 at least in part1 the machinery of heredity4 ,this understanding makes the germ substance perpetual and continuous1 and explains why successive generations are alike4 ,it does not explain1 indeed1 why an individual inherits from its parents1 but why it is like its parents4 ,while biologists are still in dispute over many problems connected with heredity1 all are agreed to-day that this principle of the continuity of the heredity substance must be the basis of all attempts to understand the machinery of heredity4 ,but plainly this whole process is a function of the cell machinery4 ,while1 therefore1 the idea of the continuity of germ substance greatly simplifies our problem1 we must acknowledge that once more we are thrown back upon the mysteries of the cell4 ,until we can more fully explain the cell machine we must recognize our inability to solve the fundamental question of why an individual is like its parents4 ,illustration3 ,,fig4 #ej4--;,diagram illustrating the principle of heredity4 ,a represents an egg of a starfish4 ,from one half1 the unshaded portion1 develops the starfish of the next generation1 ,b4 ,the other is distributed without change in the ovaries1 ov1 of the individual1 ,b4 ,from these ovaries arises the next egg1 ,a'1 with its germ plasm4 ,this germ plasm is evidently identical with that in ,a1 since it is merely a bit of the same handed down through the individual1 ,b4 ,in the development of the next generation the process is repeated1 and hence ,b' will be like ,b1 and the third generation of eggs identical with the first and second4 ,the undifferentiated part of the germ plasm is thus simply handed on from one generation to the next4 ,but plainly reproduction and heredity1 as we have thus far considered them1 will be unable to account for the slow modification of the machine2 for in accordance with the facts thus far outlined1 each generation would be precisely like the last1 and there would be no chance for development and change from generation to generation4 ,if the individual is simply the unfolding of the powers possessed by a bit of germ plasm1 and if this germ plasm is simply handed on from generation to generation1 the successive generations must of necessity be identical4 ,but the living machine has been built by changes in the successive generation1 and hence plainly some other factor is needed4 ,this factor is variation4 ,variation4--,variation is the principle that produces modification of type4 ,heredity1 as just explained1 would make all generations alike4 ,but nothing is more certain than that they are not alike4 ,the fact of variation is patent on every side1 for no two individuals are alike4 ,successive generations differ from each other in one respect or another4 ,birds vary in the length of their bills or toes2 butterflies1 in their colours2 dogs1 in their size and shape and markings2 and so on through an endless category4 ,plants and animals alike throughout nature show variations in the greatest profusion4 ,it is these variations which must furnish us with the foundation of the changes which have gradually built up the living machine4 ,of the fact of these variations there is no question1 and the matter need not detain us4 ,every one has had too many experiences to ask for proof4 ,of the nature of the variations1 however1 there are some points to be considered which are very germane to our subject4 ,in the first place1 we must notice that these variations are of two kinds4 ,there is one class which is born with the individual1 so that they are present from the time of birth4 ,in saying that these variations are born with the individual we do not necessarily mean that they are externally apparent at birth4 ,a child may inherit from its parents characters which do not appear till adult life4 ,for example1 a child may inherit the colour of its father's hair1 but this colour is not apparent at birth4 ,it appears only in later life1 but it is none the less an inborn character4 ,in the same way1 we may have many inborn variations among individuals which do not make themselves seen until adult life1 but which are none the less innate4 ,the offspring of the same parents may show decided differences1 although they are put under similar conditions1 and such differences are of course inherent in the nature of the individual4 ,such variations are called congenital variations4 ,there is1 however1 a second class of variations which are not born in the individual1 but which arise as the result of some conditions affecting its after-life4 ,the most extreme instances of this kind are mutilations4 ,some men have only one leg because the other has been lost by accident4 ,here is a variation acquired as the result of circumstances4 ,a blacksmith differs from other members of his race in having exceptionally large arm muscles2 but here1 again1 the large muscles have been produced by use4 ,a ,european who has lived under a tropical sun has a darkened skin1 but this skin has evidently been darkened by the action of the sun1 and is quite a different thing from the dark skin of the dark races of men4 ,in such instances we have variations produced in individuals as the result of outside influences acting upon them4 ,they are not inborn1 but are secondarily acquired by each individual4 ,we call them acquired variations4 ,it is not always possible to distinguish between these two types of variation4 ,frequently a character will be found in regard to which it is impossible to determine whether it is congenital or acquired4 ,if a child is born under the tropical sun1 how can we tell whether its dark skin was the result of direct action of the sun on its own skin1 or was an inheritance from its dark-skinned parents8 ,we might suppose that this could be answered by taking a similar child1 bringing it up away from the tropical sun1 and seeing whether his skin remained dark4 ,this would not suffice1 however2 for if such a child did then develop a white skin1 we could not tell but that this lighter-coloured skin had been produced by the direct bleaching effect of the northern climate upon a skin which otherwise would have been dark4 ,in other words1 a conclusive answer can not here be given4 ,it is not our purpose1 however1 to attempt to distinguish between these two kinds of variations1 but simply to recognize that they occur4 ,our next problem must be to search for an explanation of these variations4 ,with the acquired variations we have no particular trouble1 for they are easily explained as due to the direct action of the environment upon animals4 ,one of the fundamental characters of the living protoplasm 7using the word now in its widest sense7 is its extreme instability4 ,so unstable is it that any disturbing influence will affect it4 ,if two similar unicellular organisms are placed under different conditions they become unlike1 since their unstable protoplasm is directly affected by the surrounding conditions4 ,with higher animals the process is naturally a little more complicated2 but here1 too1 they are easily understood as part of the function of the machine4 ,one of the adjustments of the machine is such that when any organ is used more than usual the whole machine reacts in such a way as to send more blood to this special organ4 ,the result is a change in the nutrition of the organ and a corresponding variation in the individual4 ,thus acquired variations are simply functions of the action of the machine4 ,congenital variations1 however1 can not receive such an explanation4 ,being born with the individual1 they can not be produced by conditions affecting him1 but rather to something affecting the germ plasm from which he sprung4 ,the nature of the germ plasm controls the nature of the individual1 and congenital variations must consequently be due to its variations4 ,but it is not so easy to see how this germ plasm can undergo variation4 ,the conditions which surround the individual would affect its body1 but it is not easy to believe that they would affect the germinal substance4 ,indeed1 it is not easy to see how any external conditions can have influence upon this germinal material if it is not an active part of the body1 but is simply stored within it for future use in reproduction4 ,how could any changes in the environment of the individual have any effect upon this dormant material stored within it8 ,but if we are correct in regarding this germ material in the reproductive bodies as the basis of heredity and the guiding force in development1 then it follows that the only way in which congenital variations can occur is by some variations in the germ plasm4 ,if a child developed from germ plasm identical with that from which its parents developed1 it would inherit identical characters2 and if there are any congenital variations from its parents1 they must be due to some variations in the germ plasm4 ,in other words1 in order to explain congenital variations we must account for variations in the germ plasm4 ,now1 there are two methods by which we may suppose that these variations in the germ may arise4 ,the first is by the direct influence upon the germ plasm of certain unknown external conditions4 ,the life substance of organisms is always very unstable1 and1 as we have seen1 acquired variations are caused by external influences directly affecting it4 ,now1 the hereditary material is also life substance1 and it is plainly a possibility for us to imagine that this germ material is also subject to influences from the conditions surrounding it4 ,that such variations do occur appears to be hardly doubtful1 although we do not know what sort of influences can produce them4 ,if the germ plasm is wholly stored within the reproductive gland1 it is certainly in a position to be only slightly affected by surrounding conditions which affect the animal4 ,we can readily understand that the use of an organ like the arm will affect it in such a way as to produce changes in its protoplasm1 but we can hardly imagine that such use of the arm would produce any change in the hereditary substance which is stored in the reproductive organs4 ,external conditions may thus readily affect the body1 but not so readily the germ material4 ,even if such material is distributed more or less over the body instead of being confined to the reproductive glands1 as some believe1 the difficulty is hardly lessened4 ,this difficulty of understanding how the germ plasm can be affected by external conditions has led one school of biologists to deny that it is subject to any variation by external conditions1 and hence that all modification of the germ plasm must come from some other source4 ,probably no one1 however1 holds this position to-day1 and it is the general belief that the germ plasm may be to some slight extent modified by external conditions4 ,of course1 if such variations do occur in the germ plasm they will become congenital variations of the next generation1 since the next generation is the unfolding of the germ plasm4 ,the second method by which the variations of germ plasm may arise is apparently of more importance4 ,it is based upon the fact that1 with all higher animals and plants at least1 each individual has two parents instead of one4 ,in our study of cells we have seen that the machinery of the cell is such that it requires in the ordinary process of reproduction the union of germinal material from two different individuals to produce a cell which can develop into a new individual4 ,as we have seen1 the egg gets rid of half its chromosomes in order to receive an equal number from a male parent2 and thus the fertilized egg contains chromosomes1 and hence hereditary material1 from two different individuals4 ,now1 this sexual reproduction occurs very widely in the organic world4 ,among some of the lowest forms of unicellular organisms it is not known1 but in most others some form of such union is universal4 ,now1 here is plainly an abundant opportunity for congenital variations2 for it is seen that each individual does not come from germ material identical with that from which either parent came1 but from some of this material mixed with a similar amount from a different parent4 ,now1 the two parents are never exactly alike1 and hence the germ plasm which each contributes to the offspring will not be exactly alike4 ,the offspring will thus be the result of the unfolding of a bit of germ plasm which will be different from that from which either of its parents developed1 and these differences will result in congenital variations4 ,sexual reproduction thus results in congenital variations2 and if congenital variations are necessary for the evolution of the living machine--and we shall soon see reason for believing that they are--we find that sexual reproduction is a device adopted for bringing out such congenital variations4 ,inheritance of ,variations4--,the reason why congenital variations are needed for the evolution of the living machine is clear enough4 ,evanescent variations can have no effect upon this machine1 for they would disappear with the individual in which they appeared4 ,in order that they should have any influence in the process of machine building they must be permanent ones2 or1 in other words1 they must be inherited from generation to generation4 ,only as such variations are transmitted by heredity can they be added to the structure of the developing machine4 ,therefore we must ask whether the variations are inherited4 ,in regard to the congenital variations there can be no difficulty4 ,the very fact that they are congenital shows us that they have been produced by variations in the germ plasm1 and as such they must be transmitted1 not only to the next generation1 but to all following generations1 until the germ plasm becomes again modified4 ,this germ plasm is handed on from generation to generation with all its variations1 and hence the variations will be added permanently to the machine4 ,congenital variations are thus a means for permanently modifying the organism1 and by their agency must we in large measure believe that evolution through the ages has taken place4 ,with the acquired variations the matter stands quite differently4 ,we can readily understand how influences surrounding an animal may affect its organs4 ,the increase in the size of the muscles of the blacksmith's arm by use we understand readily enough4 ,but with our understanding of the machinery of heredity we can not see how such an effect can extend to the next generation4 ,it is only the organ directly affected that is modified by external conditions4 ,acquired variations will appear in the part of the body influenced by the changed conditions4 ,but the germ plasm within the reproductive glands is not1 so far as we can see1 subject to the influence of an increased use1 for example1 in the arm muscles4 ,the germ material is derived from the parents1 and1 if it is simply stored in the individual1 how could an acquired variation affect it8 ,if an individual lose a limb his offspring will not be without a corresponding limb1 for the hereditary material is in the reproductive organs1 and it is impossible to believe that the loss of the limb can remove from the hereditary material in the reproductive glands just that part of the germ plasm which was designed for the production of the limb4 ,so1 too1 if the germ plasm is simply stored in the individual1 it is impossible to conceive any way that it can be affected by the conditions around the individual in such a way as to explain the inheritance of acquired variations4 ,if acquired variations do not affect the germ plasm they cannot be inherited1 and if the germ plasm is only a bit of protoplasmic substance handed down from generation to generation1 we can not believe that acquired variations can influence it4 ,from such considerations as these have arisen two quite different views among biologists2 and1 while it is not our purpose to deal with disputed points1 these views are so essential to our subject that they must be briefly referred to4 ,one class of biologists adhere closely to the view already outlined1 and insist for this reason that acquired variations can not under any conditions be inherited4 ,they insist that all inherited variations are congenital1 and due therefore to direct variations in the germ plasm1 and that all instances of seeming inheritance of acquired variations are capable of other explanation4 ,the other school is equally insistent that there are abundant instances of the inheritance of acquired characters1 claiming that these proofs are so strong as to demand their acceptance4 ,hence this class of biologists insist that the explanation of heredity given as a simple handing down from generation to generation of a germ plasm is not complete1 and that while it is doubtless the foundation of heredity1 it must be modified in some way so as to admit of the inheritance of acquired characters4 ,there is no question that has excited such a wide interest in the biological world during the last fifteen years as this one of the inheritance of acquired characters4 ,until about #ahhd the question was not seriously raised4 ,heredity was known to be a fact1 and it was believed that while congenital characters are more commonly inherited1 acquired characters may also frequently be handed down from generation to generation4 ,the facts which we have noted of the continuity of germ plasm have during the last fifteen years led many biologists to deny the possibility of the latter4 ,the debate which arose has continued vigorously1 and can not be regarded as settled at the present time4 ,one result of this debate is clear4 ,it has been shown beyond question that while the inheritance of congenital characters is the rule1 the inheritance of acquired characters is at all events unusual4 ,at the present time many naturalists would be inclined to think that the balance of evidence indicates that under certain conditions certain kinds of acquired characters may be inherited1 although this is still disputed by others4 ,into this discussion we cannot enter here4 ,the reason for referring to it at all is1 however1 evident4 ,we are searching for nature's method of building machines4 ,it is perfectly clear that variations among animals and plants are the foundations of the successive steps in advance made in this machine building1 but of course only such variations as can be transmitted to posterity can serve any purpose in this development4 ,if therefore it should prove that acquired characters can not be inherited1 then we should no longer be able to look upon the direct influence of the surroundings as a factor in the machine building4 ,we should then have nothing left except the congenital variations produced by sexual union1 or the direct variation of the germ plasm as a factor for advance4 ,if1 however1 it shall prove that acquired characters may even occasionally be inherited1 then the direct effect of the environment upon the individual will serve as a decided assistance in our problem4 ,here1 then1 we have before us the factors which have been concerned in the building of the living machine under nature's hands4 ,reproduction keeps in existence a constantly active1 unstable1 readily modified organism as a basis upon which to build4 ,variation offers constantly new modifications of the type1 while heredity insures that the modifications produced in the machine by the influences which give rise to the variations shall be permanently fixed4 ,method of ,machine ,building4--,natural ,selection4 ,the method by which these factors have worked together to build up the living machines is easily understood in its general aspects1 although there are many details as yet unsolved4 ,the general facts connected with the evolution of animals are matters of common knowledge4 ,we need do no more than outline the subject1 since it is well understood by all4 ,the basis of the method is natural selection1 which acts in this machine building something as follows3 ,the law of reproduction1 as we have seen1 produces new individuals with extraordinary rapidity1 and as a result more individuals are born than can possibly find sustenance in the world4 ,hence only a few of the offspring of any animal or plant can live long enough to produce offspring in turn4 ,the many must die that the few may live2 and there is1 therefore1 a constant struggle among the individuals that are born for food or for room in the world4 ,in this struggle for existence of course the weakest will go to the wall1 while those that are best adapted for their place in life will be the ones to get food1 live1 and reproduce their kind4 ,this is at all events true among the lower animals1 although with mankind the law hardly applies4 ,now1 among the individuals that are born there will be no two exactly alike1 since variations are universal1 many of which are congenital and thus born with the individual and transmitted by inheritance4 ,clearly enough those animals that have a variation which makes them a little better adapted for the struggle will be the ones to live and hence to produce offspring1 while those without such advantage will be the ones to die4 ,we may suppose1 for example1 that some of the individuals had longer necks than the average4 ,in time of scarcity of food these individuals would be able to get food that the short-necked individuals could not reach4 ,hence in times of famine the long-necked individuals would be the ones to survive4 ,now if this peculiarity were a congenital variation it would be already represented in the germ plasm1 and consequently it would be inherited by the next generation4 ,the short-necked individuals being largely destroyed in this struggle for food1 it would follow that the next generation would be a little better off than the last1 since all would inherit this tendency toward a long neck4 ,a few generations would then see the disappearance of all individuals which did not show either this or some other corresponding advantage1 and in this way the lengthened neck would be added permanently as a part of the machine4 ,when this time came this peculiarity would no longer give its possessors any advantage over its rivals1 since all would possess it4 ,now1 therefore1 some new variation would in the same way determine which animals should live and which should die in the struggle1 and in time a new modification would be added to the machine4 ,and thus this process continues1 one variation after another being added1 until the machine is slowly built into a more and more complicated structure1 always active but with a constantly increasing efficiency4 ,the construction is a natural one4 ,a mixing of germ plasm in sexual reproduction or some other agencies produce congenital variations2 natural selection acting upon the numerous progeny selects the best of the new variations1 and heredity preserves and hands them down to posterity4 ,all students of whatever school recognize the force of this principle and look upon natural selection as an efficient agency in machine building4 ,it is probably the most fundamental of the external laws that have guided the process4 ,there are1 however1 certain other laws which have played a more or less subordinate part4 ,the chief of these are the influence of migration and isolation1 and the direct influence of the environment4 ,each of these laws has its own school of advocates1 and each has been given by its advocates the chief role in the process of machine building4 ,migration and ,isolation4--,the production of the various types of machines has been undoubtedly facilitated by the migrations of animals and the isolation of different groups of descendants from each other by various natural barriers4 ,the variations which occur in organisms are so great that they would sometimes run into abnormal structures were it not for the fact that sexual reproduction constantly tends to reduce them4 ,in an open country where animals and plants interbreed freely1 it will commonly happen that individuals with certain peculiarities will mate with others without such peculiarities1 and the offspring will therefore inherit the peculiarity not in increased degree but in decreased degree4 ,this constant interbreeding of individuals will tend to prevent the formation of many modifications in the machine which become started by variations4 ,now plainly if some such individuals1 with a peculiar variation1 should migrate into a new territory or become isolated from their relatives which do not have similar variations1 these individuals will be obliged to breed with each other4 ,the result will be that the next generation1 arising thus from two parents each of which shows the same variation1 will show it also in equal or increased degree4 ,migrations and isolations will thus tend to fix in the machine variations which sexual union or other influences inaugurate4 ,now in the history of the earth's surface there have been many changes which tend to bring about such migration and isolations1 and this factor has doubtless played a more or less important part in the building of the machines4 ,how great a part we cannot say1 nor is it necessary for our purpose to decide2 for in all these cases the machine building has only been the result of the hereditary transmission of congenital variation under certain peculiar conditions4 ,the fundamental process is the same as already considered1 only the details of its working being in question4 ,direct ,influence of the ,environment4--,under this head we have a subject of great importance4 ,it is an undoubted fact that the environment has a very decided effect upon the machine4 ,these direct effects of the environment are very positive and in great variety4 ,the tropical sun darkens the human skin2 cold climate stunts the growth of plants2 lack of food dwarfs all animals and plants1 and hundreds of other similar examples could be selected4 ,another class of similar influences are those produced by use and disuse4 ,beyond question the use of an organ tends to increase its size1 and disuse to decrease it4 ,combats of animals with each other tend to increase their strength1 flight from enemies their running powers1 etc4 ,now all these effects are direct modifications of the machine1 and if they are only transmitted to following generations so as to become permanent modifications1 they will be most important agencies in the machine building4 ,if1 on the other hand1 they are not transmitted by heredity1 they can have no permanent effect4 ,we have here thus again the problem of the inheritance of acquired characters4 ,we have already noticed the uncertainty surrounding this subject1 but the almost universal belief in the inheritance of such characters requires us to refer to it again4 ,it is uncertain whether such direct effects have any influence upon the offspring1 and therefore whether they have anything to do with this machine building4 ,still1 there are many facts which point strongly in this direction4 ,for example1 as we study the history of the horse family we find that an originally five-toed animal began to walk more and more on its middle toe1 in such a way that this toe received more and more use1 while the outer toes were used less and less4 ,now that such a habit would produce an effect upon the toes in any generation is evident2 but apparently this influence extended from generation to generation1 for1 as the history of the animals is followed1 it is found that the outer toes became smaller and smaller with the lapse of ages1 while the middle one became correspondingly larger1 until there was finally produced the horse with its one toe only on each foot4 ,now here is a line of descent or machine building in the direct line of the effects of use and disuse1 and it seems very natural to suppose that the modification has been produced by the direct effect of the use of the organs4 ,there are many other similar instances where the line of machine building has been quite parallel to the effects of use and disuse4 ,if1 therefore1 acquired characters can be inherited to any extent1 we have1 in the direct influences of the environment an important agency in machine building4 ,this direct effect of the conditions is apparently so manifest that one school of biologists finds in it the chief cause of the variations which occur1 telling us that the conditions surrounding the organism produce changes in it1 and that these variations1 being handed down to subsequent generations1 constitute the basis of the development of the machine4 ,if this factor is entirely excluded1 we are driven back upon the natural selection of congenital variations as the only kind of variations which can permanently effect the modification of the machine4 ,consciousness4--,it may be well here to refer to one other factor in the problem1 because it has somewhat recently been brought into prominence4 ,this factor is consciousness on the part of the animal4 ,among plants and the lower animals this factor can have no significance1 but consciousness certainly occurs among the higher animals4 ,just when or how it appeared are questions which are not answered1 and perhaps never will be4 ,but consciousness1 after it had once made its appearance1 became a controlling factor in the development of the machine4 ,it must not be understood by this that animals have had any consciousness of the development of their body1 or that they have made any conscious endeavours to modify its development4 ,this has not always been understood4 ,it has been frequently supposed that the claim that consciousness has an influence upon the development of an animal means that the animal has made conscious efforts to develop in certain directions4 ,for example1 it has been suggested that the tiger1 conscious of the advantage of being striped1 had a desire to possess stripes1 and the desire caused their appearance4 ,this is absurd4 ,consciousness has been a factor in the development of the machine1 but an indirect one4 ,consciousness leads to effort1 and effort has a direct influence in development4 ,for example1 an animal is conscious of hunger1 and this leads to efforts on his part to obtain food4 ,his efforts to obtain food may lead to migration or to the adoption of new kinds of food or to conflicts with various kinds of rivals1 and all of these efforts are potent factors in determining the direction of development4 ,consciousness1 again1 may lead certain animals to take pleasure in each other's society1 or to recognize that in mutual association they have protection against common enemies4 ,such a consciousness will give rise to social habits1 and social habits are a very potent factor in determining the direction in which the inherited variations will tend2 not1 perhaps1 because it effects the variations themselves1 but rather because it determines which variations among the many shall be preserved and which rejected by natural selection4 ,consciousness may lead the antelope to recognize that he has no chance in a combat with a lion1 and this will induce him to flee4 ,the habit of flight would then develop the power of flight1 not because the antelope desired such power1 but because the animals with variations which gave increased power of flight would be the ones to escape the lion1 while the slower ones would die without offspring4 ,thus consciousness would indirectly1 though not directly1 result in the lengthening of the legs of the animal and in the strengthening of his running muscles4 ,beyond a doubt this factor of consciousness has been a factor of no little moment in the development of the higher types of organic machines4 ,we can as yet only dimly understand its action1 but it must hereafter be counted as one of the influences in the evolution of the living machine4 ,but1 after all1 these are only questions of the method of the action of certain well demonstrated1 fundamental factors4 ,whether by natural selection1 or by the inheritance of acquired characters produced by the environment1 or whether by the effect of isolation of groups of individuals1 the machine building has always been produced in the same way4 ,a machine1 either through the direct influence of the environment1 or as a result of sexual combination of germ plasm1 shows a variation from its parents4 ,this variation proves of value to its possessor1 who lives and transmits it permanently to posterity4 ,thus step by step1 one part is added to another1 until the machine has grown into the intricately adapted structure which we call the animal or plant4 ,this has been nature's method of building machines1 all based upon the three properties possessed by the living cell--reproduction1 variation1 and heredity4 ,summary of ,nature's ,power of ,building ,machines4--,let us now notice the position we have reached4 ,our problem in the present chapter has been to find out whether nature possesses forces adequate to explain the building of machines with their parts accurately adapted to each other so as to act harmoniously for certain ends4 ,astronomy has shown that she has forces for the building of worlds2 geology1 that she has forces for making mountain and valley2 and chemistry1 that she has forces for building chemical compounds4 ,but the organism is neither a world1 nor a mass of matter1 nor a chemical compound4 ,it is a machine4 ,has nature any forces for machine building8 ,we have found that by the use of the three factors1 reproduction1 variation1 and heredity1 nature is able to produce a machine of ever greater and greater complexity1 with the parts all adapted to each other4 ,now the difference between a machine and a mass of matter is simply in the adaptation of parts to act harmoniously for definite ends4 ,hence if we are allowed these three factors1 we can say that nature does possess forces adequate to the manufacture of machines4 ,these forces are not chemical forces1 and the construction of the machine has thus been brought about by forces entirely different from those which produced the chemical molecule4 ,but we have plainly not reached the bottom of the matter in our attempt to explain the machinery of living things4 ,we have based the whole process upon three factors4 ,reproduction1 variation1 and heredity are the properties of all living matter2 but they are not1 like gravity and chemism1 universal forces of nature4 ,they occur in living organisms only4 ,why should they occur in living organisms1 and here alone8 ,these three properties are perhaps the most marvellous properties of nature2 and surely we have not finished our task if we have based the whole process of machine building upon these mysterious phenomena1 leaving them unintelligible4 ,we must therefore now ask whether we can proceed any farther and find any explanation of these fundamental powers of the living machine4 ,it must be confessed that here we are at present forced to stop4 ,we can proceed no further with any certainty1 or even probability4 ,we may say that variation and heredity are only phases of reproduction1 and reproduction is a property of the living cell4 ,we may say that this power of reproduction is dependent upon the power of assimilation and growth1 for cell division is a result of cell growth4 ,we may further say that growth and assimilation are chemical processes resulting from the oxidation of food1 and that thus all of these processes are to be reduced to chemical forces4 ,in this way we may seem to have a chemical foundation for life phenomena4 ,but clearly this is far from satisfactory4 ,in the first place1 it utterly fails to explain why the living cell has these properties1 while no other body possesses them1 nor why they are possessed by living protoplasms alone1 ceasing instantly with death4 ,indeed it does not tell us what death can be4 ,secondly1 it utterly fails to explain the marvels of cell division with resulting hereditary transmission4 ,for all this we must fall back upon the structure of protoplasm1 and say that the cell machinery is so adjusted that the machine1 when acting as a whole1 is capable of transforming the energy of chemical composition in certain directions4 ,these fundamental properties are then the properties of the cell machine just as surely as printing is the property of the printing press4 ,we can no more account for the life phenomena by chemical powers than we can for printing by chemical forces manifested in the burning of the coal in the engine room4 ,to be sure1 it is the chemical forces in the engine room that furnishes the energy1 but it is the machinery of the press that explains the printing4 ,so1 while chemical forces supply life energy1 it is the cell machinery that must explain the fundamental living factors4 ,so long as this machine is intact it can continue to run and perform its duties4 ,but it is a very delicate machine and is easily broken4 ,when it is broken its activities cease4 ,a broken machine can not run4 ,it is dead4 ,in short1 we come back once more to the idea of the machinery of protoplasm1 and must base our understanding of its properties upon its structure4 ,it is proper to state that there are still some biologists who insist that the ultimate explanation of protoplasm is purely chemical and that life phenomena may be manifested in mixtures of compounds that are purely physical mixtures and not machines4 ,it is claimed that much of this cell structure described above is due to imperfection in microscopic methods and does not really exist in living protoplasm1 while the marvellous activities described are found only in the highly organized cell1 but do not belong to simple protoplasm4 ,it is claimed that simple protoplasm consists of a physical mixture of two different compounds which form a foam when thus mixed1 and that much of the described structure of protoplasm is only the appearance of this foam4 ,this conception is certainly not the prevalent one to-day2 and even if it should be the proper one1 it would still leave the cell as an extremely complicated machine4 ,under any view the cell is a mechanism and must be resolved into subordinate parts4 ,it may be uncertain whether these subordinate parts are to be regarded simply as chemical compounds physically mixed1 or as smaller units each of which is a smaller mechanism4 ,at all events1 at the present time we know of no such simple protoplasm capable of living activities apart from machinery1 and the problem of explaining life1 even in the simplest form known1 remains the problem of explaining a mechanism4 ,the ,origin of the ,cell ,machine4--,we have thus set before us another problem1 which is after all the fundamental one1 namely1 to ask whether we can tell anything of nature's method of building the protoplasmic machine4 ,the building of the higher animal and plant1 as we have seen1 is the result of the powers of protoplasm2 but protoplasm itself is a machine4 ,what has been its history8 ,we must first notice that no notion of chemical evolution helps us out4 ,it has been a favourite thought with some that the origin of the first living thing was the result of chemical evolution4 ,as the result of physical forces there was produced1 from the original nebulous mass1 a more and more complicated system until the world was formed4 ,then chemical phenomena became more and more complicated until1 with the production of more and more complicated compounds1 protoplasm was finally produced4 ,a few years ago1 under the impulse of the idea that protoplasm was a compound1 or at least a simple mixture of compounds1 this thought of protoplasm as the result of chemical evolution was quite significant4 ,physical forces1 chemical forces1 and vital forces1 explain successively the origin of worlds1 protoplasm1 and organisms4 ,this conception has1 however1 no longer much significance4 ,we know of no such living chemical compound apart from cell machinery4 ,a new conception of protoplasm has arisen which demands a different explanation of its origin4 ,since it is a machine rather than a compound1 mechanical rather than chemical forces are required for its explanation4 ,have we then any suggestion as to the method of the origin of this protoplasmic machine8 ,our answer must1 at the present1 be certainly in the negative4 ,the complexity of the cell tells us plainly that it can not be the ultimate living substance which may have arisen from chemical evolution4 ,it is made up of parts delicately adapted to act in harmony with each other1 and its activity depends upon the relation of these parts4 ,whatever chemical forces may have accomplished1 they never could have combined different bodies into linin1 centrosomes1 chromosomes1 etc41 which1 as we have seen1 are the basis of cell life4 ,to account for this machine1 therefore1 we are driven to assume either that it was produced by some unknown intelligent power in its present condition of complex adjustment1 or to assume that it has had a long history of building by successive steps1 just as we have seen to be the case with the higher organisms4 ,the latter assumption is1 of course1 in harmony with the general trend of thought4 ,to-day protoplasm is produced only from other protoplasm2 but1 plainly1 the first protoplasm on the earth must have had a different origin4 ,we must therefore next look for facts which will enable us to understand its origin4 ,we have seen that the animal and plant machines have been built up from the simple cell as the result of its powers acting under the ordinary conditions of nature4 ,now1 in accordance with this general line of thought1 we shall be compelled to assume that previous to the period of building machinery which we have been considering1 there was another period of machine building during which this cell machine was built by certain natural forces4 ,but here we are forced to stop1 for nothing which we yet know gives even a hint as to the method by which this machine was produced4 ,we have1 however1 seen that there are forces in nature efficient in building machines1 as well as those for producing chemical compounds2 and this1 doubtless1 suggests to us that there may be similar forces at work in building protoplasm4 ,if we can find natural forces by which the simplest bit of living matter can be built up into a complicated machine like the ox1 with its many delicately adjusted parts1 it is certainly natural to imagine that the same forces may have built this simpler machine with which we started4 ,but such a conclusion is for a simple reason impossible4 ,we have seen that the essential factor in this machine building is reproduction1 with the correlated powers of variation and heredity4 ,without these forces we could not have advanced in this machine building at all4 ,but these properties are themselves the result of the machinery of protoplasm4 ,we have no reason for thinking that this property of reproduction can occur in any other object in nature except this protoplasmic machine4 ,of course1 then1 if reproduction is the result of the structure of protoplasm we can not use this factor in explaining the origin of this protoplasm4 ,the powers of the completed machine can not be brought forward to account for its origin4 ,thus the one fundamental factor for machine building is lacking1 and if we are to explain nature's method of producing protoplasm from simpler structures1 we must either suppose that the parts of the cell are capable of reproduction and subject to heredity1 or we must look for some other method4 ,such a road has however not yet been found1 nor have we any idea in what direction to look4 ,but the fact that nature has methods of machine building1 as we have seen1 may hold out the possibility that some day we may discover her method of building this primitive living machine1 the cell4 ,it is useless to try to go further at present4 ,the origin of living matter is shrouded in as great obscurity as ever4 ,we must admit that the disclosures of the modern microscope have complicated rather than simplified this problem4 ,while a few years ago chemists and biologists were eagerly expecting to discover a method of manufacturing a bit of living matter by artificial means1 that hope has now been practically abandoned4 ,the task is apparently hopeless4 ,we can manipulate chemical forces and produce an endless series of chemical compounds4 ,but we can not manipulate the minute bits of matter which make up the living machine4 ,since living matter is made of the adjustment of these microscopic parts of matter1 we can not hope to make a bit of living matter until we find some way of making these little parts and adjusting them together4 ,most students of protoplasm have therefore abandoned all expectation of making even the simplest living thing4 ,we are apparently as far from the real goal of a natural explanation of life as we were before the discovery of protoplasm4 ,general ,summary4--,it is now desirable to close this discussion of seemingly somewhat unconnected topics by bringing them together in a brief summary4 ,this will enable us to see more clearly the position in which science stands to-day upon this matter of the natural explanation of living phenomena1 and to picture to ourselves more concisely our knowledge of the living machine4 ,the problem we have set before us is to find out to what extent it is possible to account for vital phenomena by the application of ordinary natural laws and forces1 and therefore to find out whether it is necessary to assume that there are forces needed to explain life which are different from those found in other realms of nature1 or whether vital forces are all correlated with physical forces4 ,it has been evident at a glance that the living body is a machine4 ,like other machines it consists of parts adjusted to each other for the accomplishment of definite ends1 and its action depends upon the adjustment of its parts4 ,like other machines1 it neither creates nor destroys energy1 but simply converts the potential energy of its foods into some form of active energy1 and1 like other machines1 its power ceases when the machine is broken4 ,with this understanding the problem clearly resolved itself into two separate ones4 ,the first was to determine to what extent known physical and chemical laws and forces are adequate to an explanation of the various phenomena of life4 ,the second was to determine whether there are any known forces which can furnish a natural explanation of the origin of the living machine4 ,manifestly1 if the first of these problems is insolvable1 the second is insolvable also4 ,in the study of the first problem we have reached the general conclusion that the secondary phenomena of life are readily explained by the application of physical and chemical forces acting in the living machine4 ,these secondary phenomena include such processes as the digestion and absorption of food1 circulation1 respiration1 excretion1 bodily motion1 etc4 ,nervous phenomena also doubtless come under this head1 at least so far as concerns nervous force4 ,we have been obliged1 however1 to exclude from this correlation the mental phenomena4 ,mental phenomena can not as yet be measured1 and have not yet been shown to be correlated with physical energy4 ,in other words1 it has not yet been proved that mental force is energy at all2 and if it is not energy1 then of course it can not be included in the laws which govern the physical energy of the universe4 ,although a close relation exists between physical changes in the brain cells and mental phenomena1 no further connection has yet been drawn between mental power and physical force4 ,all other secondary phenomena1 however1 are intelligently explained by the action of natural forces in the machinery of the living organism4 ,while we have thus found that the secondary phenomena of life are intelligible as the result of the structure of the machine1 certain other fundamental phenomena have been constantly forcing themselves upon our attention as a foundation of these secondary activities4 ,the power of contraction1 the power of causing certain kinds of chemical change to occur which result in metabolism1 the property of sensibility1 the property of reproduction--these are fundamental to all living activity1 and are1 after all1 the real phenomena which we wish to explain4 ,but these are not peculiar to the complicated machines4 ,we can discard all the apparent machinery of the animal or plant and find these properties still developed in the simplest bit of living matter4 ,to learn their significance1 therefore1 we have turned to the study of the simplest form of matter in which these fundamental properties are manifested4 ,this led us at once to the study of the so-called protoplasm1 for protoplasm is the simplest known form of matter that is alive4 ,protoplasm itself at first seemed to be a homogeneous body1 and was looked upon as a chemical compound of high complexity4 ,if this were true its properties would depend upon its composition and would be explained by the action of chemical forces4 ,such a conception would have quickly solved the problem1 for it would reduce living properties to chemical powers4 ,but the conception proved to be delusive4 ,protoplasm1 at least the simplest form known to possess the fundamental life properties1 soon showed itself to be no chemical compound1 but a machine of wonderful intricacy4 ,the fundamental phenomena of life and of protoplasm have proved to be both chemical and mechanical4 ,metabolism is the result of the oxidation of food1 and motion is an instance of transference of force4 ,our problem then resolved itself into finding the power that guides the action of these natural forces4 ,food will not undergo such an oxidation except in the presence of protoplasm1 nor will the phenomena of metabolism occur except in the presence of living protoplasm4 ,clearly1 then1 the living protoplasm contains within itself the power of guiding this play of chemical force in such a way as to give rise to vital phenomena1 and our search must be not for chemical force but for this guiding principle4 ,our study of protoplasm has told us clearly enough that we must find this guiding principle in the interaction of the machinery within the protoplasm4 ,the microscope has told us plainly that these fundamental principles are based upon machinery4 ,the cell division 7reproduction7 is apparently controlled by the centrosomes2 the heredity by the chromosomes2 the constructive metabolism by the nucleus in general1 while the destructive metabolism is also seated in the cell substance outside the nucleus4 ,whether these statements are strictly accurate in detail does not particularly affect the general conclusion4 ,it is clearly enough demonstrated that the activities of the protoplasmic body are dependent upon the relation of its different parts4 ,although we have got rid of the complicated machinery of the organism in general1 we are still confronted with the machinery of the cell4 ,but our analysis can not1 at present1 go further4 ,our knowledge of this machine has not as yet enabled us to gain any insight as to its method of action4 ,we can not yet conceive how this machine controls the chemical and physical forces at its disposal in such a way as to produce the orderly result of life4 ,the strict correlation between the forces of the physical universe and those manifested by this protoplasm tells us that a transformation of energy occurs within it1 but of the method of that transformation we as yet know nothing4 ,irritability1 movement1 metabolism1 and reproduction appear to be not chemical properties of a compound1 but mechanical properties of a machine4 ,our mechanical analysis of the living machine stops short before it reaches any foundation in the chemical forces of nature4 ,it is thus clearly apparent that the phenomena of life are dependent upon the machinery of living things1 and we have therefore the second question of the origin of this machinery to answer4 ,chemical forces and mechanical forces have been laboriously investigated1 but neither appear adequate to the manufacture of machines4 ,they produce only chemical compounds and worlds with their mountains and seas4 ,the construction of artificial machines has demanded intelligence4 ,but here is a natural machine--the organism4 ,it is the only machine produced by natural methods1 so far as we know2 and we have therefore next asked whether there are1 in nature1 simple forces competent to build machines such as living animals and plants8 ,in pursuance of this question we have found that the complicated machines have been built out of the simpler ones by the action of known forces and laws4 ,the factors in this machine building are simply those of the fundamental vital properties of the simplest protoplasmic machine4 ,reproduction1 heredity1 and variation1 acting under the ever-changing conditions of the earth's surface1 are apparently all that are needed to explain the building of the complex machines out of the simpler ones4 ,nature has forces adequate to the building of machines as well as forces adequate to the formation of chemical compounds and worlds4 ,but here again we are unable to base our explanation upon chemical and physical forces4 ,reproduction1 heredity1 and variation are properties of the cell machine1 and we are therefore thrown back upon the necessity of explaining the origin of this machine4 ,can we find a mechanical or chemical explanation of the origin of protoplasm8 ,a chemical explanation of the cell is impossible1 since it is not a chemical compound1 but a piece of mechanism4 ,the explanation given for the origin of animals and plants is also here apparently impossible4 ,the factors upon which that explanation depended are factors of this completed machine itself1 and can not be used to explain its origin4 ,we are left at present therefore without any foundation for further advance4 ,the cells must have had a history of construction1 but we do not as yet conceive any forces which may be looked upon as contributing to that history4 ,whether life phenomena can be manifested by any mixture of compounds simpler than the cell we do not yet know4 ,the great problems still remaining for solution1 which have hardly been touched by modern biology in all its endeavours to find a mechanical explanation of the living machine1 are1 therefore1 three4 ,first1 the relation of mentality to the general phenomena of the correlation of force2 second1 the intelligible understanding of the mechanism of protoplasm which enables it to guide the blind chemical and physical forces of nature so as to produce definite results2 third1 the kind of forces which may have contributed to the origin of that simplest living machine upon whose activities all vital phenomena rest--the living cell4 ,,index4 ,a4 ,absorption of food1 #bj4 ,acquired characters1 inheritance of1 #afd1 #afe1 #aff1 #afg1 #aga4 --variations1 #aei1 #afj4 ,amoeba1 #gc4 ,anatomical evidence for evolution1 #adb4 ,aquacity1 #hj4 ,arm compared with wing1 #add4 ,aristotle1 #a4 ,assimilation1 #hj1 #abd1 #adi1 #agf4 ,asters of dividing cells1 #ih4 ,b4 ,barry1 #fc1 #fd4 ,bathybias1 #hd4 ,biology a new science1 #a1 #e1 #ae4 ,blood1 #ce1 #cf1 #ch1 #fi1 #gc4 ,blood-vessels1 #ce1 #cf4 ,body as a machine1 #bb1 #be1 #di4 ,bone cells1 #fi4 ,building of the living machine1 #aca1 #acd1 #acf1 #acg1 #afg1 #age1 #ahj4 ,c4 ,cartilage cells1 #fh4 ,cell as a machine1 #abf1 #abh4 --description of1 #fi4 --division1 #ie1 #if1 #aja4 --discovery of1 #eh4 --doctrine1 #fj4 --substance1 #fe1 #abe4 ,cells1 #ef1 #hd1 #hf1 #aah1 #aai4 ,cellular structure of organisms1 #fe4 ,cell wall1 #fd1 #gb4 ,centrosome1 #id1 #if1 #ig1 #aja1 #ajc1 #aje1 #aaj4 ,challenger expedition1 #hc4 ,chemical evolution1 #agi4 ,chemical theory of vitality1 #ad2 of life1 #gh1 #aaf4 ,chemism or mechanism1 #eg1 #agf4 ,chemistry of digestion1 #bg1 #bh2 of protoplasm1 #gf2 of respiration1 #ch4 ,chromatin1 #ib1 #id1 #if1 #ajb1 #adi1 #aec4 ,chromosomes1 #ig1 #ih1 #aja1 #aje1 #ajh1 #aaj1 #aac1 #aeb4 ,circulation1 #cd4 ,colonies of cells1 #he4 ,comparison of the body and a machine1 #bb4 ,congenital variations1 #aeh1 #afj1 #afc2 inheritance of1 #afd4 ,connective-tissue cells1 #gj4 ,conservation of energy1 #g1 #ag4 ,consciousness as a factor in machine building1 #agc4 ,constructive chemical processes1 #ej1 #ea1 #eb1 #abd4 ,continuity of germ plasm1 #aee4 ,correlation of vital and physical forces1 #ac1 #af1 #bb1 #bc1 #bd1 #be4 ,cytoblastema4 #fb4 ,cytology1 #aj4 ,d4 ,darwin1 #ha4 ,death of the cell1 #abg4 ,decline of the reign of protoplasm1 #he4 ,destructive chemical processes1 #ej1 #ea1 #eb1 #abe4 ,dialysis1 #bi1 #cj1 #ca4 ,digestion1 #bg4 ,e4 ,egg1 #ajc1 #abj1 #aeb4 division of1 #fc4 ,egg1 fertilization of1 #ajb4 ,embryological evidence for evolution1 #adj4 ,energy of nervous impulse1 #dc1 #ed4 ,environment1 #aga4 ,evidence for evolution as a method of machine building1 #aci1 #ade4 ,evolution1 #i1 #af1 #ha1 #acd4 ,experiments with developing eggs1 #aba4 ,f4 ,fat1 absorption of1 #cb4 ,female pronucleus1 #aaj4 ,fern cells1 section of1 #fg4 ,fertilization of the egg1 #ie1 #ajb2 significance of1 #aab4 ,fibres in protoplasm1 #hg2 --in spindle1 #ih1 #aja4 ,forces at work in machine building1 #adh1 #agf1 #aha4 ,formed material1 #fd4 ,free cell formation1 #fd4 ,g4 ,geological evidence for evolution1 #aci4 ,germ plasm1 #aed4 ,h4 ,heart as a pump1 #ce4 ,heat1 #bd1 #dd1 #de4 ,heredity1 #adh1 #aej1 #agf2 --explanation of1 #aeb4 ,hereditary traits1 #aac1 #aec4 ,historical geology1 #f4 ,history of the living machine1 #acc1 #adg4 ,horses' toes1 loss of1 #agb4 ,huxley1 #aa1 #ge1 #hc1 #hd4 ,i4 ,irritability1 #ed4 ,isolation1 theory of1 #agj4 ,k4 ,karyokinesis1 #if1 #aja4 ,kidneys1 #da4 ,l4 ,leaf1 section of1 #ff4 ,life the result of a mechanism1 #aae1 #agg4 ,linin1 #ib1 #ajc4 ,linnus1 #a4 ,lyell1 #f4 ,lymph1 #cf1 #cg4 ,m4 ,machine defined1 #bj4 ,machines the result of mechanical forces1 #aaf4 ,male cell1 #ajd1 #ajg4 ---- pronucleus1 #aji4 ,maturation of the egg1 #ajd4 ,mechanical nature of living organisms1 #ab4 ,mechanical theory of life1 #ha1 #add4 ,membrane of the nucleus1 #ib1 #aja4 ,mental phenomena1 #dg1 #dh4 ,metabolism1 #ed4 ,microsomes1 #hg4 ,migration1 theory of1 #agj4 ,monera1 #hh4 ,movement1 #ed4 ,muscle1 #cf1 #ga4 ,n4 ,natural selection1 #afg4 ,nerve-fibre cell1 #gj4 ,nervous energy1 #db1 #dd4 ---- system1 #da4 ,new biological problems1 #ae4 ,nucleolus1 #fe1 #ib1 #id4 ,nucleus1 #fe1 #hd1 #hg1 #ic1 #aja1 #ajc1 #aac1 #abd1 #adi2 formation of new1 #aja4 ---- function of1 #hi1 #ij1 #ie4 ---- presence of1 #hg1 #hh1 #hi4 ---- structure of1 #ia4 ,o4 ,organic chemistry1 #gh4 ,organic compounds1 artificial manufacture of1 #gh1 #hb4 ,origin of cell machine1 #agh1 #agi1 #ahj4 ,origin of life1 #ha1 #ahb4 ,osmosis1 #bi4 ,oxidation1 #hj1 #agf4 ---- as a vital process1 #ci1 #ef4 ,p4 ,philosophical biology1 #d4 ,physical basis of life1 #ge4 ,polar cells1 #ajg4 ,potato1 section of cells1 #fg4 ,properties of chemical compounds1 #gi4 ,protoplasm1 #ad1 #gd1 #hb1 #hc1 #hd1 #aad1 #aae1 #agi4 ---- artificial manufacture of1 #hb4 ---- as a machine1 #hf1 #agh4 ---- discovery of1 #gd4 ---- nature of1 #gf4 ---- structure of1 #hf1 #hg4 ,purpose vs4 cause1 #aa1 #ab4 ,r4 ,reaction against the cell doctrine1 #aag4 ,reign of law1 #d4 ---- of the nucleus1 #ia4 ---- of protoplasm1 #ha1 #he4 ,relationship1 significance of1 #adc4 ,removal of waste1 #ci1 #dj4 ,reproduction1 #ed1 #hj1 #abd1 #adh1 #agf2 --rapidity of1 #adi4 ,respiration1 #cg4 ,reticulum of cell1 #hg2 --of nucleus1 #ib4 ,root tip1 section of1 #ff4 ,s4 ,schultze1 #gd1 #ge4 ,schwann1 #fa1 #fb1 #gb4 ,secretion1 #ci1 #dj4 ,segmentation nucleus1 #aaj4 ,sensations1 #df4 ,separation of chromosomes1 #ajj4 ,sexual reproduction1 #ajb4 ,spermatozoan1 #ajg1 #aji1 #aed4 ,splitting of chromosomes1 #ii4 ,spindle fibres1 #aja4 ,struggle for existence1 #afh4 ,summary of ,part ,i1 #abh4 ---- general1 #ahb4 ,u4 ,undifferentiated protoplasm1 #hc4 ,unicellular animals1 #ga4 ,units of vital activity1 #ec4 ,use and disuse1 #aga1 #agb4 ,v4 ,variation1 #adh1 #aeg1 #afj1 #agf4 ,variation from sexual union1 #afb4 ,variation in germ plasm1 #afa4 ,vegetative functions1 #da4 ,villi1 #ca4 ,vital force1 vitality1 #ac1 #ae1 #cd1 #cg1 #eb1 #hj1 #he4 ,vital properties1 #ed2 --located in cells1 #abc4 ,w4 ,wing compared with arm1 #add4 ,wood cells1 #fh4 ,,the ,,end4 ,,the ,,library ,,of ,,useful ,,stories4 ,illustrated4 #afmo4 ,cloth1 #ce cents net per volume2 postage1 #d cents per volume additional4 ,the ,story of a ,grain of ,wheat4 ,by ,w4,c4 ,,edgar4 ,the ,story of ,alchemy4 ,by ,m4,m4 ,,pattison ,,muir4 ,the ,story of ,animal ,life4 ,by ,b4 ,,lindsay4 ,the ,story of the ,art of ,music4 ,by ,f4,j4 ,,crowest4 ,the ,story of the ,art of ,building4 ,by ,p4,l4 ,,waterhouse4 ,the ,story of ,king ,alfred4 ,by ,sir ,,walter ,,besant4 ,the ,story of ,books4 ,by ,,gertrude ,b4 ,,rawlings4 ,the ,story of the ,alphabet4 ,by ,,edward ,,clodd4 ,the ,story of ,eclipses4 ,by ,g4,f4 ,,chambers1 ,f4,r4,a4,s4 ,the ,story of the ,living ,machine4 ,by ,h4,w4 ,,conn4 ,the ,story of the ,british ,race4 ,by ,,john ,,munro1 ,c4,e4 ,the ,story of ,geographical ,discovery4 ,by ,,joseph ,,jacobs4 ,the ,story of the ,cotton ,plant4 ,by ,f4 ,,wilkinson1 ,f4,g4,s4 ,the ,story of the ,mind4 ,by ,prof4 ,j4 ,,mark ,,baldwin4 ,the ,story of ,photography4 ,by ,,alfred ,t4 ,,story4 ,the ,story of ,life in the ,seas4 ,by ,,sydney ,j4 ,,hickson4 ,the ,story of ,germ ,life4 ,by ,prof4 ,h4,w4 ,,conn4 ,the ,story of the ,earth's ,atmosphere4 ,by ,,douglas ,,archibald4 ,the ,story of ,extinct ,civilizations of the ,east4 ,by ,,robert ,,anderson1 ,m4,a41 ,f4,a4,s4 ,the ,story of ,electricity4 ,by ,,john ,,munro1 ,c4,e4 ,the ,story of a ,piece of ,coal4 ,by ,e4,a4 ,,martin1 ,f4,g4,s4 ,the ,story of the ,solar ,system4 ,by ,g4,f4 ,,chambers1 ,f4,r4,a4,s4 ,the ,story of the ,earth4 ,by ,h4,g4 ,,seeley1 ,f4,r4,s4 ,the ,story of the ,plants4 ,by ,,grant ,,allen4 ,the ,story of ,primitive ,man4 ,by ,,edward ,,clodd4 ,the ,story of the ,stars4 ,by ,g4,f4 ,,chambers1 ,f4,r4,a4,s4 ,,others ,,in ,,preparation4 ,d4 ,,appleton ,,and ,,company1 ,,new ,,york4 ,,new ,,edition ,,of ,,huxley',s ,,essays4 ,collected ,essays4 ,by ,,thomas ,h4 ,,huxley4 ,new complete edition1 with revisions1 the ,essays being grouped according to general subject4 ,in nine volumes1 a new ,introduction accompanying each volume4 #abmo4 ,cloth1 #a4be per volume4 ,,volume4 ,i4 ,methods and ,results4 ,,ii4 ,darwiniana4 ,,iii4 ,science and ,education4 ,,iv4 ,science and ,hebrew ,tradition4 ,v4 ,science and ,christian ,tradition4 ,,vi4 ,hume4 ,,vii4 ,man's ,place in ,nature4 ,,viii4 ,discourses1 ,biological and ,geological4 ,,ix4 ,evolution and ,ethics1 and ,other ,essays4 ,mr4 ,huxley has covered a vast variety of topics during the last quarter of a century4 ,it gives one an agreeable surprise to look over the tables of contents and note the immense territory which he has explored4 ,to read these books carefully and studiously is to become thoroughly acquainted with the most advanced thought on a large number of topics4--,new ,york ,herald4 ,d4 ,,appleton ,,and ,,company1 ,,new ,,york4 ,d4 ,,appleton ,,and ,,company',s ,,publications4 ,,pioneers ,,of ,,evolution1 from ,thales to ,huxley ,by ,,edward ,,clodd1 ,president of the ,folk-,lore ,society2 ,author of ,the ,story of ,creation1 ,the ,story of ',primitive' ,man1 etc4 ,with ,portraits1 #abmo4 ,cloth1 #a4ej4 ,the mass of interesting material which ,mr4 ,clodd has got together and woven into a symmetrical story of the progress from ignorance and theory to knowledge and the intelligent recording of fact is prodigious4444 ,the 'goal' to which ,mr4 ,clodd leads us in so masterly a fashion is but the starting point of fresh achievements1 and1 in due course1 fresh theories4 ,his book furnishes an important contribution to a liberal education4--,london ,daily ,chronicle4 ,we are always glad to meet ,mr4 ,clodd4 ,he is never dull2 he is always well informed1 and he says what he has to say with clearness and precision4444 ,the interest intensifies as ,mr4 ,clodd attempts to show the part really played in the growth of the doctrine of evolution by men like ,wallace1 ,darwin1 ,huxley1 and ,spencer4444 ,we commend the book to those who want to know what evolution really means4--,london ,times4 ,this is a book which was needed4444 ,altogether1 the book could hardly be better done4 ,it is luminous1 lucid1 orderly1 and temperate4 ,above all1 it is entirely free from personal partisanship4 ,each chief actor is sympathetically treated1 and friendship is seldom or never allowed to overweight sound judgment--,london ,academy4 ,we can assure the reader that he will find in this work a very useful guide to the lives and labors of leading evolutionists of the past and present4 ,especially serviceable is the account of ,mr4 ,herbert ,spencer and his share in rediscovering evolution1 and illustrating its relations to the whole field of human knowledge4 ,his forcible style and wealth of metaphor make all that ,mr4 ,clodd writes arrestive and interesting4--,london ,literary ,world4 ,can not but prove welcome to fair-minded men4444 ,to read it is to have an object-lesson in the meaning of evolution4444 ,there is no better book on the subject for the general reader4444 ,no one could go through the book without being both refreshed and newly instructed by its masterly survey of the growth of the most powerful idea of modern times4--,the ,scotsman4 ,d4 ,,appleton ,,and ,,company1 ,,new ,,york4 ,,books ,,on ,,social ,,science4 ,socialism ,new and ,old4 ,by ,prof4 ,,william ,,graham1 #abmo4 ,cloth1 #a4ge4 ,professor ,graham's book may be confidently recommended to all who are interested in the study of socialism1 and not so intoxicated with its promises of a new heaven and a new earth as to be impatient of temperate and reasoned criticism4--,london ,times4 ,professor ,graham presents an outline of the successive schemes of three writers who have chiefly influenced the development of socialism1 and dwells at length upon the system of ,rousseau1 that of ,st4 ,simon1 and on that of ,karl ,marx1 the founder of the new socialism1 'which has gained favor with the working classes in all civilized countries1' which agrees with ,rousseau's plan in being democratic1 and with ,st4 ,simon's in aiming at collective ownership4444 ,the professor is an independent thinker1 whose endeavor to be clear has resulted in the statement of definite conclusions4 ,the book is a remarkably fair digest of the subject under consideration4--,philadelphia ,ledger4 ,dynamic ,sociology3 ,or1 ,applied ,social ,science1 as based upon ,statical ,sociology and the less ,complex ,sciences4 ,by ,,lester ,f4 ,,ward1 ,a4,m4 ,in #b vols4 #abmo4 ,cloth1 #d4jj4 ,a book that will amply repay perusal4444 ,recognizing the danger in which sociology is1 of falling into the class of dead sciences or polite amusements1 ,mr4 ,ward has undertaken to 'point out a method by which the breath of life can be breathed into its nostrils4'--,rochester ,post-,express4 ,mr4 ,ward has evidently put great labor and thought into his two volumes1 and has produced a work of interest and importance4 ,he does not limit his effort to a contribution to the science of sociology4444 ,he believes that sociology has already reached the point at which it can be and ought to be applied1 treated as an art1 and he urges that 'the ,state' or ,government now has a new1 legitimate1 and peculiar field for the exercise of intelligence to promote the welfare of men4--,new ,york ,times4 ,criminal ,sociology4 ,by ,prof4 ,e4 ,,ferri4 ,a new volume in the ,criminology ,series1 edited by ,w4 ,douglas ,morrison1 #abmo4 ,cloth1 #a4ej4 ,in this volume ,professor ,ferri1 a distinguished member of the ,italian ,parliament1 deals with the conditions which produce the criminal population1 and with the methods by which this anti-social section of the community may be diminished4 ,he divides the causes of crime into two great classes1 individual and social4 ,the individual causes consist of physical and mental defects2 the social causes consist of social disadvantages of every description4 ,his view is that the true remedy against crime is to remove individual defects and social disadvantages where it is possible to remove them4 ,he shows that punishment has comparatively little effect in this direction1 and is apt to divert attention from the true remedy--the individual and social amelioration of the population as a whole4 ,d4 ,,appleton ,,and ,,company1 ,,new ,,york4 ,,books ,,for ,,nature ,,lovers4 ,insect ,life4 7,new ,edition in ,colors47 ,by ,,john ,,henry ,,comstock1 ,professor of ,entomology in ,cornell ,university4 ,with #ab full-page plates reproducing butterflies and various insects in their natural colors1 and with many wood engravings by ,anna ,botsford ,comstock1 ,member of the ,society of ,american ,wood ,engravers1 #abmo4 ,cloth1 #a4ge net2 postage1 #bj cents additional4 ,the volume is admirably written1 and the simple and lucid style is a constant delight4444 ,it is sure to serve an excellent purpose in the direction of popular culture1 and the love of natural science which it will develop in youthful minds can hardly fail to bear rich fruit4--,boston ,beacon4 ,familiar ,fish3 ,their ,habits and ,capture4 ,a ,practical ,book on ,fresh-,water ,game ,fish4 ,by ,,eugene ,,mccarthy4 ,with an ,introduction by ,dr4 ,david ,starr ,jordan1 ,president of ,leland ,stanford ,junior ,university1 and numerous ,illustrations1 #abmo4 ,cloth1 #a4ej4 ,one of the handsomest1 most practical1 most informing books that we know4 ,the author treats his subject with scientific thoroughness1 but with a light touch that makes the book easy reading4444 ,the book should be the companion of all who go a-fishing4--,new ,york ,mail and ,express4 ,the ,art of ,taxidermy4 ,by ,,john ,,rowley1 ,chief of the ,department of ,taxidermy in the ,american ,museum of ,natural ,history4 ,illustrated1 #abmo4 ,cloth1 #b4jj4 ,mr4 ,rowley will long be gratefully remembered by taxidermists1 amateurs1 and others1 for the care he has used in thus meeting a long-felt want4--,bangor1 ,me41 ,sportsman4 ,the book is not an elaborate treatise upon the abstract principles which lie at the foundation of artistic taxidermy1 but is rather a compendium full of practical hints and suggestions1 recipes1 and formulas for the working taxidermist4--,the ,dial4 ,plants4 7,plant ,relations and ,plant ,structures in one volume47 ,by ,,john ,m4 ,,coulter1 ,a4,m41 ,ph4,d41 ,head of ,department of ,botany1 ,university of ,chicago1 #abmo4 ,cloth1 #a4hj net4 7,one of the ,twentieth ,century ,text-,books47 ,d4 ,,appleton ,,and ,,company1 ,,new ,,york4 ,,evolution ,,of ,,man ,,and ,,christianity4 ,new edition4 ,by the ,rev4 ,,howard ,,macqueary4 ,with a new ,preface1 in which the ,author answers his ,critics1 and with some important ,additions1 #abmo4 ,cloth1 #a4ge4 ,this is a revised and enlarged edition of a book published last year4 ,the author reviews criticisms upon the first edition1 denies that he rejects the doctrine of the incarnation1 admits his doubts of the physical resurrection of ,christ1 and his belief in evolution4 ,the volume is to be marked as one of the most profound expressions of the modern movement toward broader theological positions4--,brooklyn ,times4 ,,history ,,of ,,the ,,conflict ,,between ,,religion ,,and ,,science4 ,by ,dr4 ,,john ,,william ,,draper4 #abmo4 ,cloth1 #a4ge4 ,the keynote to this volume is found in the antagonism between the progressive tendencies of the human mind and the pretensions of ecclesiastical authority1 as developed in the history of modern science4 ,no previous writer has treated the subject from this point of view1 and the present monograph will be found to possess no less originality of conception than vigor of reasoning and wealth of erudition4--,new ,york ,tribune4 ,a ,,critical ,,history ,,of ,,free ,,thought ,,in ,,reference ,,to ,,the ,,christian ,,religion4 ,by ,rev4 ,canon ,,adam ,,storey ,,farrar1 ,d4,d41 ,f4,r4,s41 etc4 #abmo4 ,cloth1 #a4ej4 ,a conflict might naturally be anticipated between the reasoning faculties of man and a religion which claims the right1 on superhuman authority1 to impose limits on the field or manner of their exercise4 ,it is the chief of the movements of free thought which it is my purpose to describe1 in their historic succession and their connection with intellectual causes4 ,we must ascertain the facts1 discover the causes1 and read the moral4--,the ,author4 ,,creation ,,or ,,evolution8 ,a ,philosophical ,inquiry4 ,by ,,george ,,ticnor ,,curtis4 #abmo4 ,cloth1 #b4jj4 ,a treatise on the great question of ,creation or ,evolution by one who is neither a naturalist nor theologian1 and who does not profess to bring to the discussion a special equipment in either of the sciences which the controversy arrays against each other1 may seem strange at first sight2 but ,mr4 ,curtis will satisfy the reader1 before many pages have been turned1 that he has a substantial contribution to make to the debate1 and that his book is one to be treated with respect4 ,his part is to apply to the reasonings of the men of science the rigid scrutiny with which the lawyer is accustomed to test the value and pertinency of testimony1 and the legitimacy of inferences from established facts4--,new ,york ,tribune4 ,d4 ,,appleton ,,and ,,company1 ,,new ,,york4