,,the ,,story ,,of ,,germ ,,life  ,,by  
,h4 ,w4 ,,conn  ,,professor ,,of        
,,biology ,,at ,,wesleyan ,,university1 
,,author ,,of ,,evolution ,,of          
,,to-,,day1 ,,the ,,living ,,world1     
,,etc4      ,,preface4   ,since the     
first edition of this book was published
 the popular idea of bacteria to which  
attention was drawn in the original     
preface has undergone considerable      
modification4 ,experimental medicine has
 added constantly to the list of        
diseases caused by bacterial organisms1 
and the general public has been educated
 to an adequate conception of the       
importance of the germ as the chief     
agency in the transmission of disease1  
with corresponding advantage to the     
efficiency of personal and public       
hygiene4 ,at the same time knowledge of 
the benign bacteria and the enormous    
role they play in the industries and the
 arts has become much more widely       
diffused4 ,bacteriology is being studied
 in colleges as one of the cultural     

sciences2 it is being widely adopted as 
a subject of instruction in high        
schools2 and schools of agriculture and 
household science turn out each year    
thousands of graduates familiar with the
 functions of bacteria in daily life4   
,through these agencies the popular     
misconception of the nature of micro-   
organisms and their relations to man is 
being gradually displaced by a general  
appreciation of their manifold services4
 ,it is not unreasonable to hope that   
the many thousands of copies of this    
little manual which have been circulated
 and read have contributed materially to
 that end4 ,if its popularity is a safe 
criterion1 the book has amply fulfilled 
its purpose of placing before the       
general reader in a simple and direct   
style the main facts of bacteriology4   
,beginning with a discussion of the     
nature of bacteria1 it shows their      
position in the scale of plant and      
animal life4 ,the middle chapters       
describe the functions of bacteria in   

the arts1 in the dairy1 and in          
agriculture4 ,the final chapters discuss
 the relation of bacteria to disease and
 the methods by which the new and       
growing science of preventive medicine  
combats and counteracts their dangerous 
powers4  ,,july1 #aiae4      ,,contents4
   ,i4--,,bacteria ,,as ,,plants        
,historical4--,form of                  
bacteria4--,multiplication of           
bacteria4--,spore                       
formation4--,motion4--,internal         
structure4--,animals or plants8--       
,classification4--,variation4--,where   
bacteria are found4                     
,,ii4--,,miscellaneous ,,uses ,,of      
,,bacteria ,,in ,,the ,,arts4           
,maceration                             
industries4--,linen4--,jute4--,hemp4--,s
ponges4--,leather4 --,fermentative      
industries4--,vinegar--,lactic          
acid4--,butyric acid4-- ,bacteria in    
tobacco curing4--,troublesome           
fermentations4  ,,iii4--,,bacteria ,,in 
,,the ,,dairy4  ,sources of bacteria in 

milk4--,effect of bacteria on milk4--   
,bacteria used in butter                
making4--,bacteria in cheese making4    
,,iv4--,,bacteria ,,in ,,natural        
,,processes4  ,bacteria as              
scavengers4--,bacteria as agents in     
,nature's food cycle4--,relation of     
bacteria to agriculture4--,sprouting of 
seeds4 --,the silo4--,the fertility of  
the soil4--,bacteria as sources of      
trouble to the farmer4--,coal formation4
  ,v4--,,parasitic ,,bacteria ,,and     
,,their ,,relation ,,to ,,disease       
,method of producing                    
disease4--,pathogenic germs not strictly
 parasitic4--,pathogenic germs that are 
true parasites4--,what diseases are due 
to bacteria4--,variability of pathogenic
 powers4-- ,susceptibility of the       
individual4--,recovery from             
bacteriological diseases4--,diseases    
caused by organisms other than bacteria4
  ,,vi4--,,methods ,,of ,,combating     
,,parasitic ,,bacteria  ,preventive     
medicine4--,bacteria in                 

surgery4--,prevention by                
inoculation4--,limits of preventive     
medicine4--,curative medicine4          
--,drugs--,vis medicatrix               
naturae4--,antitoxines and their use4-- 
,conclusion4      ,,the ,,story ,,of    
,,germ ,,life4   ,,chapter ,i4          
,,bacteria ,,as ,,plants4   ,during the 
last fifteen years the subject of       
bacteriology ,footnote3 ,the term       
microbe is simply a word which has been 
coined to include all of the microscopic
 plants commonly included under the     
terms bacteria and yeasts4 has developed
 with a marvellous rapidity4 ,at the    
beginning of the ninth decade of the    
century bacteria were scarcely heard of 
outside of scientific circles1 and very 
little was known about them even among  
scientists4 ,today they are almost      
household words1 and everyone who reads 
is beginning to recognise that they have
 important relations to his everyday    
life4 ,the organisms called bacteria    
comprise simply a small class of low    

plants1 but this small group has proved 
to be of such vast importance in its    
relation to the world in general that   
its study has little by little          
crystallized into a science by itself4  
,it is a somewhat anomalous fact that a 
special branch of science1 interesting  
such a large number of people1 should be
 developed around a small group of low  
plants4 ,the importance of bacteriology 
is not due to any importance bacteria   
have as plants or as members of the     
vegetable kingdom1 but solely to their  
powers of producing profound changes in 
,nature4 ,there is no one family of     
plants that begins to compare with them 
in importance4 ,it is the object of this
 work to point out briefly how much both
 of good and ill we owe to the life and 
growth of these microscopic organisms4  
,as we have learned more and more of    
them during the last fifty years1 it has
 become more and more evident that this 
one little class of microscopic plants  
fills a place in ,nature's processes    

which in some respects balances that    
filled by the whole of the green plants4
 ,minute as they are1 their importance  
can hardly be overrated1 for upon their 
activities is founded the continued life
 of the animal and vegetable kingdom4   
,for good and for ill they are agents of
 neverceasing and almost unlimited      
powers4  ,,historical4  ,the study of   
bacteria practically began with the use 
of the microscope4 ,it was toward the   
close of the seventeenth century that   
the ,dutch microscopist1 ,leeuwenhoek1  
working with his simple lenses1 first   
saw the organisms which we now know     
under this name1 with sufficient        
clearness to describe them4 ,beyond     
mentioning their existence1 however1 his
 observations told little or nothing4   
,nor can much more be said of the       
studies which followed during the next  
one hundred and fifty years4 ,during    
this long period many a microscope was  
turned to the observation of these      
minute organisms1 but the majority of   

observers were contented with simply    
seeing them1 marvelling at their        
minuteness1 and uttering many           
exclamations of astonishment at the     
wonders of ,nature4 ,a few men of more  
strictly scientific natures paid some   
attention to these little organisms4    
,among them we should perhaps mention   
,von ,gleichen1 ,muller1 ,spallanzani1  
and ,needham4 ,each of these1 as well as
 others1 made some contributions to our 
knowledge of microscopical life1 and    
among other organisms studied those     
which we now call bacteria4             
,speculations were even made at these   
early dates of the possible causal      
connection of these organisms with      
diseases1 and for a little the medical  
profession was interested in the        
suggestion4 ,it was impossible then1    
however1 to obtain any evidence for the 
truth of this speculation1 and it was   
abandoned as unfounded1 and even        
forgotten completely1 until revived     
again about the middle of the #aith     

century4 ,during this century of wonder 
a sufficiency of exactness was1 however1
 introduced into the study of           
microscopic organisms to call for the   
use of names1 and we find ,muller using 
the names of ,monas1 ,proteus1 ,vibrio1 
,bacillus1 and ,spirillum1 names which  
still continue in use1 although commonly
 with a different significance from that
 given them by ,muller4 ,muller did     
indeed make a study sufficient to       
recognise the several distinct types1   
and attempted to classsify these bodies4
 ,they were not regarded as of much     
importance1 but simply as the most      
minute organisms known4  ,nothing of    
importance came from this work1 however1
 partly because of the inadequacy of the
 microscopes of the day1 and partly     
because of a failure to understand the  
real problems at issue4 ,when we        
remember the minuteness of the bacteria1
 the impossibility of studying any one  
of them for more than a few moments at a
 time --only so long1 in fact1 as it can

 be followed under a microscope2 when we
 remember1 too1 the imperfection of the 
compound microscopes which made high    
powers practical impossibilities2 and1  
above all1 when we appreciate the       
looseness of the ideas which pervaded   
all scientists as to the necessity of   
accurate observation in distinction from
 inference1 it is not strange that the  
last century gave us no knowledge of    
bacteria beyond the mere fact of the    
existence of some extremely minute      
organisms in different decaying         
materials4 ,nor did the #aith century   
add much to this until toward its       
middle4 ,it is true that the microscope 
was vastly improved early in the        
century1 and since this improvement     
served as a decided stimulus to the     
study of microscopic life1 among other  
organisms studied1 bacteria received    
some attention4 ,ehrenberg1 ,dujardin1  
,fuchs1 ,perty1 and others left the     
impress of their work upon bacteriology 
even before the middle of the century4  

,it is true that ,schwann shrewdly drew 
conclusions as to the relation of       
microscopic organisms to various        
processes of fermentation and           
decay--conclusions which1 although not  
accepted at the time1 have subsequently 
proved to be correct4 ,it is true that  
,fuchs made a careful study of the      
infection of blue milk1 reaching the    
correct conclusion that the infection   
was caused by a microscopic organism    
which he discovered and carefully       
studied4 ,it is true that ,henle made a 
general theory as to the relation of    
such organisms to diseases1 and pointed 
out the logically necessary steps in a  
demonstration of the causal connection  
between any organism and a disease4 ,it 
is true also that a general theory of   
the production of ail kinds of          
fermentation by living organisms had    
been advanced4 ,but all these           
suggestions made little impression4 ,on 
the one hand1 bacteria were not         
recognised as a class of organisms by   

themselves--were not1 indeed1           
distinguished from yeasts or other      
minute animalcuise4 ,their variety was  
not mistrusted and their significance   
not conceived4 ,as microscopic          
organisms1 there were no reasons for    
considering them of any more importance 
than any other small animals or plants1 
and their extreme minuteness and        
simplicity made them of little interest 
to the microscopist4 ,on the other hand1
 their causal connection with           
fermentative and putrefactive processes 
was entirely obscured by the            
overshadowing weight of the chemist     
,liebig1 who believed that fermentations
 and putrefactions were simply chemical 
processes4 ,liebig insisted that all    
albuminoid bodies were in a state of    
chemically unstable equilibrium1 and if 
left to themselves would fall to pieces 
without any need of the action of       
microscopic organisms4 ,the force of    
,liebig's authority and the brilliancy  
of his expositions led to the wide      

acceptance of his views and the         
temporary obscurity of the relation of  
microscopic organisms to fermentative   
and putrefactive processes4 ,the        
objections to ,liebig's views were      
hardly noticed1 and the force of the    
experiments of ,schwann was silently    
ignored4 ,until the sixth decade of the 
century1 therefore1 these organisms1    
which have since become the basis of a  
new branch of science1 had hardly       
emerged from obscurity4 ,a few          
microscopists recognised their          
existence1 just as they did any other   
group of small animals or plants1 but   
even yet they failed to look upon them  
as forming a distinct group4 ,a growing 
number of observations was accumulating1
 pointing toward a probable causal      
connection between fermentative and     
putrefactive processes and the growth of
 microscopic organisms2 but these       
observations were known only to a few1  
and were ignored by the majority of     
scientists4  ,it was ,louis ,pasteur who

 brought bacteria to the front1 and it  
was by his labours that these organisms 
were rescued from the obscurity of      
scientific publications and made objects
 of general and crowning interest4 ,it  
was ,pasteur who first successfully     
combated the chemical theory of         
fermentation by showing that albuminous 
matter had no inherent tendency to      
decomposition4 ,it was ,pasteur who     
first clearly demonstrated that these   
little bodies1 like all larger animals  
and plants1 come into existence only by 
ordinary methods of reproduction1 and   
not by any spontaneous generation1 as   
had been earlier claimed4 ,it was       
,pasteur who first proved that such a   
common phenomenon as4 the souring of    
milk was produced by microscopic        
organisms growing in the milk4 ,it was  
,pasteur who first succeeded in         
demonstrating that certain species of   
microscopic organisms are the cause of  
certain diseases1 and in suggesting     
successful methods of avoiding them4    

,all these discoveries were made in     
rapid succession4 ,within ten years of  
the time that his name began to be heard
 in this connection by scientists1 the  
subject had advanced so rapidly that it 
had become evident that here was a new  
subject of importance to the scientific 
world1 if not to the public at large4   
,the other important discoveries which  
,pasteur made it is not our purpose to  
mention here4 ,his claim to be          
considered the founder of bacteriology  
will be recognised from what has already
 been mentioned4 ,it was not that he    
first discovered the organisms1 or first
 studied them2 it was not that he first 
suggested their causal connection with  
fermentation and disease1 but it was    
because he for the first time placed the
 subject upon a firm foundation by      
proving with rigid experiment some of   
the suggestions made by others1 and in  
this way turned the attention of science
 to the study of micro-organisms4       
,after the importance of the subject had

 been demonstrated by ,pasteur1 others  
turned their attention in the same      
direction1 either for the purpose of    
verification or refutation of ,pasteur's
 views4 ,the advance was not very rapid1
 however1 since bacteriological         
experimentation proved to be a subject  
of extraordinary difficulty4 ,bacteria  
were not even yet recognised as a group 
of organisms distinct enough to be      
grouped by themselves1 but were even by 
,pasteur at first confounded with       
yeasts4 ,as a distinct group of         
organisms they were first distinguished 
by ,hoffman in #ahfi1 since which date  
the term bacteria1 as applying to this  
special group of organisms1 has been    
coming more and more into use4 ,so      
difficult were the investigations1 that 
for years there were hardly any         
investigators besides ,pasteur who could
 successfully handle the subject and    
reach conclusions which could stand the 
test of time4 ,for the next thirty      
years1 although investigators and       

investigations continued to increase1 we
 can find little besides dispute and    
confusion along this line4 ,the         
difficulty of obtaining for experiment  
any one kind of bacteria by itself1     
unmixed with others 7pure cultures71    
rendered advance almost impossible4 ,so 
conflicting were the results that the   
whole subject soon came into almost     
hopeless confusion1 and very few steps  
were taken upon any sure basis4 ,so     
difficult were the methods1 so          
contradictory and confusing the results1
 because of impure cultures1 that a     
student of to-day who wishes to look up 
the previous discoveries in almost any  
line of bacteriology need hardly go back
 of #ahhj1 since he can almost rest     
assured that anything done earlier than 
that was more likely to be erroneous    
than correct4  ,the last fifteen years  
have1 however1 seen a wonderful change4 
,the difficulties had been mostly those 
of methods of work1 and with the ninth  
decade of the century these methods were

 simplified by ,robert ,koch4 ,this     
simplification of method for the first  
time placed this line of investigation  
within the reach of scientists who did  
not have the genius of ,pasteur4 ,it was
 now possible to get pure cultures      
easily1 and to obtain with such pure    
cultures results which were uniform and 
simple4 ,it was now possible to take    
steps which had the stamp of accuracy   
upon them1 and which further experiment 
did not disprove4 ,from the time when   
these methods were thus made manageable 
the study of bacteria increased with a  
rapidity which has been fairly          
startling1 and the information which has
 accumulated is almost formidable4 ,the 
very rapidity with which the            
investigations have progressed has      
brought considerable confusion1 from the
 fact that the new discoveries have not 
had time to be properly assimilated into
 knowledge4 ,today many facts are known 
whose significance is still uncertain1  
and a clear logical discussion of the   

facts of modern bacteriology is not     
possible4 ,but sufficient knowledge has 
been accumulated and digested to show us
 at least the direction along which     
bacteriological advance is tending1 and 
it is to the pointing out of these      
directions that the following pages will
 be devoted4  ,,what ,,are ,,bacteria8  
,the most interesting facts connected   
with the subject of bacteriology concern
 the powers and influence in ,nature    
possessed by the bacteria4 ,the         
morphological side of the subject is    
interesting enough to the scientist1 but
 to him alone4 ,still1 it is impossible 
to attempt to study the powers of       
bacteria without knowing something of   
the organisms themselves4 ,to understand
 how they come to play an important part
 in ,nature's processes1 we must know   
first how they look and where they are  
found4 ,a short consideration of certain
 morphological facts will therefore be  
necessary at the start4  ,,form ,,of    
,,bacteria4  ,in shape bacteria are the 

simplest conceivable structures4        
,although there are hundreds of         
different species1 they have only three 
general forms1 which have been aptly    
compared to billiard balls1 lead        
pencils1 and corkscrews4 ,spheres1 rods1
 and spirals represent all shapes4 ,the 
spheres may be large or small1 and may  
group themselves in various ways2 the   
rods may be long or short1 thick or     
slender2 the spirals may be loosely or  
tightly coiled1 and may have only one or
 two or may have many coils1 and they   
may be flexible or stiff2 but still     
rods1 spheres1 and spirals comprise all 
types4  ,in size there is some          
variation1 though not very great4 ,all  
are extremely minute1 and never visible 
to the naked eye4 ,the spheres vary from
 #j4be u to #a4e u 7#j4jjjjab to        
#j4jjjjf inches74 ,the rods may be no   
more than #j4c u in diameter1 or may be 
as wide as #a4e u to #b4e u1 and in     
length vary all the way from a length   
scarcely longer than their diameter to  

long threads4 ,about the same may be    
said of the spiral forms4 ,they are     
decidedly the smallest living organisms 
which our microscopes have revealed4    
,in their method of growth we find one  
of the most characteristic features4    
,they universally have the power of     
multiplication by simple division or    
fission4 ,each individual elongates and 
then divides in the middle into two     
similar halves1 each of which then      
repeats the process4 ,this method of    
multiplication by simple division is the
 distinguishing mark which separates the
 bacteria from the yeasts1 the latter   
plants multiplying by a process known as
 budding4 ,fig4 #b shows these two      
methods of multiplication4  ,while all  
bacteria thus multiply by division1     
certain differences in the details      
produce rather striking differences in  
the results4 ,considering first the     
spherical forms1 we find that some      
species divide1 as described1 into two1 
which separate at once1 and each of     

which in turn divides in the opposite   
direction1 called ,micrococcus1 7,fig4  
#c74 ,other species divide only in one  
direction4 ,frequently they do not      
separate after dividing1 but remain     
attached4 ,each1 however1 again         
elongates and divides again1 but all    
still remain attached4 ,there are thus  
formed long chains of spheres like      
strings of beads1 called ,streptococci  
7,fig4 #d74 ,other species divide first 
in one direction1 then at right angles  
to the first division1 and a third      
division follows at right angles to the 
plane of the first two1 thus producing  
solid groups of fours1 eights1 or       
sixteens 7,fig #e71 called ,sarcina4    
,each different species of bacteria is  
uniform in its method of division1 and  
these differences are therefore         
indications of differences in species1  
or1 according to our present method of  
classification1 the different methods of
 division represent different genera4   
,all bacteria producing ,streptococcus  

chains form a single genus              
,streptococcus1 and all which divide in 
three division planes form another      
genus1 ,sarcina1 etc4  ,the rod-shaped  
bacteria also differ somewhat1 but to a 
less extent4 ,they almost always divide 
in a plane at right angles to their     
longest dimension4 ,but here again we   
find some species separating immediately
 after division1 and thus always        
appearing as short rods 7,fig4 #f71     
while others remain attached after      
division and form long chains4          
,sometimes they appear to continue to   
increase in length without showing any  
signs of division1 and in this way long 
threads are formed 7,fig4 #g74 ,these   
threads are1 however1 potentially at    
least1 long chains of short rods1 and   
under proper conditions they will break 
up into such short rods1 as shown in    
,fig4 #g;a4 ,occasionally a rod species 
may divide lengthwise1 but this is rare4
 ,exactly the same may be said of the   
spiral forms4 ,here1 too1 we find short 

rods and long chains1 or long spiral    
filaments in which can be seen no       
division into shorter elements1 but     
which1 under certain conditions1 break  
up into short sections4  ,,rapidity ,,of
 ,,multiplication4  ,it is this power of
 multiplication by division that makes  
bacteria agents of such significance4   
,their minute size would make them      
harmless enough if it were not for an   
extraordinary power of multiplication4  
,this power of growth and division is   
almost incredible4 ,some of the species 
which have been carefully watched under 
the microscope have been found under    
favourable conditions to grow so rapidly
 as to divide every half hour1 or even  
less4 ,the number of offspring that     
would result in the course of           
twenty-four hours at this rate is of    
course easily computed4 ,in one day each
 bacterium would produce over           
#af1ejj1jjj descendants1 and in two days
 about #bha1ejj1jjj1jjj4 ,it has been   
further calculated that these           

#bha1ejj1jjj1jjj would form about a     
solid pint of bacteria and weigh about a
 pound4 ,at the end of the third day the
 total descendants would amount to      
#dg1jjj1jjj1jjj1jjj1 and would weigh    
about #af1jjj1jjj pounds4 ,of course    
these numbers have no significance1 for 
they are never actual or even possible  
numbers4 ,long before the offspring     
reach even into the millions their rate 
of multiplication is checked either by  
lack of food or by the accumulation of  
their own excreted products1 which are  
injurious to them4 ,but the figures do  
have interest since they show faintly   
what an unlimited power of              
multiplication these organisms have1 and
 thus show us that in dealing with      
bacteria we are dealing with forces of  
almost infinite extent4  ,this wonderful
 power of growth is chiefly due to the  
fact that bacteria feed upon food which 
is highly organized and already in      
condition for absorption4 ,most plants  
must manufacture their own foods out of 

simpler substances1 like carbonic       
dioxide 7,co#b7 and water1 but bacteria1
 as a rule1 feed upon complex organic   
material already prepared by the        
previous life of plants or animals4 ,for
 this reason they can grow faster than  
other plants4 ,not being obliged to make
 their own foods like most plants1 nor  
to search for it like animals1 but      
living in its midst1 their rapidity of  
growth and multiplication is limited    
only by their power to seize and        
assimilate this food4 ,as they grow in  
such masses of food1 they cause certain 
chemical changes to take place in it1   
changes doubtless directly connected    
with their use of the material as food4 
,recognising that they do cause chemical
 changes in food material1 and          
remembering this marvellous power of    
growth1 we are prepared to believe them 
capable of producing changes wherever   
they get a foothold and begin to grow4  
,their power of feeding upon complex    
organic food and producing chemical     

changes therein1 together with their    
marvellous power of assimilating this   
material as food1 make them agents in   
,nature of extreme importance4          
,,differences ,,between ,,different     
,,species ,,of ,,bacteria4  ,while      
bacteria are thus very simple in form1  
there are a few other slight variations 
in detail which assist in distinguishing
 them4 ,the rods are sometimes very     
blunt at the ends1 almost as if cut     
square across1 while in other species   
they are more rounded and occasionally  
slightly tapering4 ,sometimes they are  
surrounded by a thin layer of some      
gelatinous substance1 which forms what  
is called a capsule 7,fig4 #aj74 ,this  
capsule may connect them and serve as a 
cement1 to prevent the separate elements
 of a chain from falling apart4         
,sometimes such a gelatinous secretion  
will unite great masses of bacteria into
 clusters1 which may float on the       
surface of the liquid in which they grow
 or may sink to the bottom4 ,such masses

 are called zoogloea1 and their general 
appearance serves as one of the         
characters for distinguishing different 
species of bacteria 7,fig4 #aj1 a and   
b74 ,when growing in solid media1 such  
as a nutritious liquid made stiff with  
gelatine1 the different species have    
different methods of spreading from     
their central point of origin4 ,a single
 bacterium in the midst of such a       
stiffened mass will feed upon it and    
produce descendants rapidly2 but these  
descendants1 not being able to move     
through the gelatine1 will remain       
clustered together in a mass1 which the 
bacteriologist calls a colony4 ,but     
their method of clustering1 due to      
different methods of growth1 is by no   
means always alike1 and these colonies  
show great differences in general       
appearance4 ,the differences appear to  
be constant1 however1 for the same      
species of bacteria1 and hence the shape
 and appearance of the colony enable    
bacteriologists to discern different    

species 7,fig4 ,,ii74 ,all these points 
of difference are of practical use to   
the bacteriologist in distinguishing    
species4  ,,spore ,,formation4  ,in     
addition to their power of reproduction 
by simple division1 many species of     
bacteria have a second method by means  
of spores4 ,spores are special rounded  
or oval bits of bacteria protoplasm     
capable of resisting adverse conditions 
which would destroy the ordinary        
bacteria4 ,they arise among bacteria in 
two different methods4  ,endogenous     
spores4--,these spores arise inside of  
the rods or the spiral forms 7,fig4     
#ab74 ,they first appear as slight      
granular masses1 or as dark points which
 become gradually distinct from the rest
 of the rod4 ,eventually there is thus  
formed inside the rod a clear1 highly   
refractive1 spherical or oval spore1    
which may even be of a greater diameter 
than the rod producing it1 thus causing 
it to swell out and become spindle      
formed ,fig4 #ab c4 ,these spores may   

form in the middle or at the ends of the
 rods 7,fig4 #ab74 ,they may use up all 
the protoplasm of the rod in their      
formation1 or they may use only a small 
part of it1 the rod which forms them    
continuing its activities in spite of   
the formation of the spores within it4  
,they are always clear and highly       
refractive from containing little water1
 and they do not so readily absorb      
staining material as the ordinary rods4 
,they appear to be covered with a layer 
of some substance which resists the     
stain1 and which also enables them to   
resist various external agencies4 ,this 
protective covering1 together with their
 small amount of water1 enables them to 
resist almost any amount of drying1 a   
high degree of heat1 and many other     
adverse conditions4 ,commonly the spores
 break out of the rod1 and the rod      
producing them dies1 although sometimes 
the rod may continue its activity even  
after the spores have been produced4    
,arthrogenous spores 7874--,certain     

species of bacteria do not produce      
spores as just described1 but may give  
rise to bodies that are sometimes called
 arthrospores4 ,these bodies are formed 
as short segments of rods4 ,a long rod  
may sometimes break up into several     
short rounded elements1 which are clear 
and appear to have a somewhat increased 
power of resisting adverse conditions4  
,the same may happen among the spherical
 forms1 which only in rare instances    
form endogenous spores4 ,among the      
spheres which form a chain of           
streptococci some may occasionally be   
slightly different from the rest4 ,they 
are a little larger1 and have been      
thought to have an increased resisting  
power like that of true spores 7,fig4   
#ac b74 ,it is quite doubtful1 however1 
whether it is proper to regard these    
bodies as spores4 ,there is no good     
evidence that they have any special     
resisting power to heat like endogenous 
spores1 and bacteriologists in general  
are inclined to regard them simply as   

resting cells4 ,the term arthrospores   
has been given to them to indicate that 
they are formed as joints or segments1  
and this term may be a convenient one to
 retain although the bodies in question 
are not true spores4  ,still a different
 method of spore formation occurs in a  
few peculiar bacteria4 ,in this case    
7,fig4 #ad7 the protoplasm in the large 
thread breaks into many minute spherical
 bodies1 which finally find exit4 ,the  
spores thus formed may not be all alike1
 differences in size being noticed4     
,this method of spore formation occurs  
only in a few special forms of bacteria4
  ,the matter of spore formation serves 
as one of the points for distinguishing 
species4 ,some species do not form      
spores1 at least under any of the       
conditions in which they have been      
studied4 ,others form them readily in   
almost any condition1 and others again  
only under special conditions which are 
adverse to their life4 ,the method of   
spore formation is always uniform for   

any single species4 ,whatever be the    
method of the formation of the spore1   
its purpose in the life of the bacterium
 is always the same4 ,it serves as a    
means of keeping the species alive under
 conditions of adversity4 ,its power of 
resisting heat or drying enables it to  
live where the ordinary active forms    
would be speedily killed4 ,some of these
 spores are capable of resisting a heat 
of #ahj degrees ,c4 7#cfj degrees ,f47  
for a short time1 and boiling water they
 can resist for a long time4 ,such      
spores when subsequently placed under   
favourable conditions will germinate and
 start bacterial activity anew4         
,,motion4  ,some species of bacteria    
have the power of active motion1 and may
 be seen darting rapidly to and fro in  
the liquid in which they are growing4   
,this motion is produced by flagella    
which protrude from the body4 ,these    
flagella 7,fig4 #ae7 arise from a       
membrane surrounding the bacterium1 but 
have an intimate connection with the    

protoplasmic content4 ,their            
distribution is different in different  
species of bacteria4 ,some species have 
a single flagellum at one end 7,fig4 #ae
 a74 ,others have one at each end 7,fig4
 #ae b74 ,others1 again1 have1 at least 
just before dividing1 a bunch at one or 
both ends 7,fig4 #ae c and d71 while    
others1 again1 have many flagella       
distributed all over the body in dense  
profusion 7,fig4 #ae e74 ,these flagella
 keep up a lashing to and fro in the    
liquid1 and the lashing serves to propel
 the bacteria through the liquid4       
,,internal ,,structure4  ,it is hardly  
possible to say much about the structure
 of the bacteria beyond the description 
of their external forms4 ,with all the  
variations in detail mentioned1 they are
 extraordinarily simple1 and about all  
that can be seen is their external      
shape4 ,of course1 they have some       
internal structure1 but we know very    
little in regard to it4 ,some           
microscopists have described certain    

appearances which they think indicate   
internal structure4 ,fig4 #af shows some
 of these appearances4 ,the matter is as
 yet very obscure1 however4 ,the        
bacteria appear to have a membranous    
covering which sometimes is of a        
cellulose nature4 ,within it is         
protoplasm which shows various uncertain
 appearances4 ,some microscopists have  
thought they could find a nucleus1 and  
have regarded bacteria as cells with    
inclosed nucleii 7,figs4 #aj a and #ae  
f74 ,others have regarded the whole     
bacterium as a nucleus without any      
protoplasm1 while others1 again1 have   
concluded that the discerned internal   
structure is nothing except an          
appearance presented by the physical    
arrangement of the protoplasm4 ,while we
 may believe that they have some        
internal structure1 we must recognise   
that as yet microscopists have not been 
able to make it out4 ,in short1 the     
bacteria after two centuries of study   
appear to us about as they did at first4

 ,they must still be described as minute
 spheres1 rods1 or spirals1 with no     
further discernible structure1 sometimes
 motile and sometimes stationary1       
sometimes producing spores and sometimes
 not1 and multiplying universally by    
binary fission4 ,with all the           
development of the modern microscope we 
can hardly say more than this4 ,our     
advance in knowledge of bacteria is     
connected almost wholly with their      
methods of growth and the effects they  
produce in ,nature4  ,,animals ,,or     
,,plants8  ,there has been in the past  
not a little question as to whether     
bacteria should be rightly classed with 
plants or with animals4 ,they certainly 
have characters which ally them with    
both4 ,their very common power of active
 independent motion and their common    
habit of living upon complex bodies for 
foods are animal characters1 and have   
lent force to the suggestion that they  
are true animals4 ,but their general    
form1 their method of growth and        

formation of threads1 and their method  
of spore formation are quite plantlike4 
,their general form is very similar to a
 group of low green plants known as     
,oscillaria4 ,fig4 #ag shows a group of 
these ,oscillariae1 and the similarity  
of this to some of the thread-like      
bacteria is decided4 ,the ,oscillariae  
are1 however1 true plants1 and are of a 
green colour4 ,bacteria are therefore   
to- day looked upon as a low type of    
plant which has no chlorophyll1         
,footnote3 ,chlorophyll is the green    
colouring matter of plants4 but is      
related to ,oscillariae4 ,the absence of
 the chlorophyll has forced them to     
adopt new relations to food1 and compels
 them to feed upon complex foods instead
 of the simple ones1 which form the food
 of green plants4 ,we may have no       
hesitation1 then1 in calling them       
plants4 ,it is interesting to notice    
that with this idea their place in the  
organic world is reduced to a small one 
systematically4 ,they do not form a     

class by themselves1 but are simply a   
subclass1 or even a family1 and a family
 closely related to several other common
 plants4 ,but the absence of chlorophyll
 and the resulting peculiar life has    
brought about a curious anomaly4        
,whereas their closest allies are known 
only to botanists1 and are of no        
interest outside of their systematic    
relations1 the bacteria are familiar to 
every one1 and are demanding the life   
attention of hundreds of investigators4 
,it is their absence of chlorophyll and 
their consequent dependence upon complex
 foods which has produced this anomaly4 
,,classification ,,of ,,bacteria4       
,while it has generally been recognised 
that bacteria are plants1 any further   
classification has proved a matter of   
great difficulty1 and bacteriologists   
find it extremely difficult to devise   
means of distinguishing species4 ,their 
extreme simplicity makes it no easy     
matter to find points by which any      
species can be recognised4 ,but in spite

 of their similarity1 there is no doubt 
that many different species exist4      
,bacteria which appear to be almost     
identical1 under the microscope prove to
 have entirely different properties1 and
 must therefore be regarded as distinct 
species4 ,but how to distinguish them   
has been a puzzle4 ,microscopists have  
come to look upon the differences in    
shape1 multiplication1 and formation of 
spores as furnishing data sufficient to 
enable them to divide the bacteria into 
genera4 ,the genus ,bacillus1 for       
instance1 is the name given to all      
rod-shaped bacteria which form          
endogenous spores1 etc4 ,but to         
distinguish smaller subdivisions it has 
been found necessary to fall back upon  
other characters1 such as the shape of  
the colony produced in solid gelatine1  
the power to produce disease1 or to     
oxidize nitrites1 etc4 ,thus at present 
the different species are distinguished 
rather by their physiological than their
 morphological characters4 ,this is an  

unsatisfactory basis of classification1 
and has produced much confusion in the  
attempts to classify bacteria4 ,the     
problem of determining the species of   
bacteria is to-day a very difficult one1
 and with our best methods is still     
unsatisfactorily solved4 ,a few species 
of marked character are well known1 and 
their powers of action so well          
understood that they can be readily     
recognised2 but of the great host of    
bacteria studied1 the large majority    
have been so slightly experimented upon 
that their characters are not known1 and
 it is impossible1 therefore1 to        
distinguish many of them apart4 ,we find
 that each bacteriologist working in any
 special line commonly keeps a list of  
the bacteria which he finds1 with such  
data in regard to them as he has        
collected4 ,such a list is of value to  
him1 but commonly of little value to    
other bacteriologists from the          
insufficiency of the data4 ,thus it     
happens that a large part of the        

different species of bacteria described 
in literature to- day have been found   
and studied by one investigator alone4  
,by him they have been described and    
perhaps named4 ,quite likely the same   
species may have been found by two or   
three other bacteriologists1 but owing  
to the difficulty of comparing results  
and the incompleteness of the           
descriptions the identity of the species
 is not discovered1 and they are        
probably described again under different
 names4 ,the same process may be        
repeated over and over again1 until the 
same species of bacterium will come to  
be known by several different names1 as 
it has been studied by different        
observers4  ,,variation ,,of ,,bacteria4
  ,this matter is made even more        
confusing by the fact that any species  
of bacterium may show more or less      
variation4 ,at one time in the history  
of bacteriology1 a period lasting for   
many years1 it was the prevalent opinion
 that there was no constancy among      

bacteria1 but that the same species     
might assume almost any of the various  
forms and shapes1 and possess various   
properties4 ,bacteria were regarded by  
some as stages in the life history of   
higher plants4 ,this question as to     
whether bacteria remain constant in     
character for any considerable length of
 time has ever been a prominent one with
 bacteriologists1 and even to-day we    
hardly know what the final answer will  
be4 ,it has been demonstrated beyond    
peradventure that some species may      
change their physiological characters4  
,disease bacteria1 for instance1 under  
certain conditions lose their powers of 
developing disease4 ,species which sour 
milk1 or others which turn gelatine     
green1 may lose their characters4 ,now1 
since it is upon just such physiological
 characters as these that we must depend
 in order to separate different species 
of bacteria from each other1 it will be 
seen that great confusion and           
uncertainty will result in our attempts 

to define species4 ,further1 it has been
 proved that there is sometimes more or 
less of a metamorphosis in the life     
history of certain species of bacteria4 
,the same species may form a short rod1 
or a long thread1 or break up into      
spherical spores1 and thus either a     
short rod1 or a thread1 or a spherical  
form may belong to the same species4    
,other species may be motile at one time
 and stationary at another1 while at a  
third period it is a simple mass of     
spherical spores4 ,a spherical form1    
when it lengthens before dividing1      
appears as a short rod1 and a short rod 
form after dividing may be so short as  
to appear like a spherical organism4    
,with all these reasons for confusion1  
it is not to be wondered at that no     
satisfactory classification of bacteria 
has been reached1 or that different     
bacteriologists do not agree as to what 
constitutes a species1 or whether two   
forms are identical or not4 ,but with   
all the confusion there is slowly being 

obtained something like system4 ,in     
spite of the fact that species may vary 
and show different properties under     
different conditions1 the fundamental   
constancy of species is everywhere      
recognised to-day as a fact4 ,the       
members of the same species may show    
different properties under different    
conditions1 but it is believed that     
under identical conditions the          
properties will be constant4 ,it is no  
more possible to convert one species    
into another than it is among the higher
 orders of plants4 ,it is believed that 
bacteria do form a group of plants by   
themselves1 and are not to be regarded  
as stages in the history of higher      
plants4 ,it is believed that1 together  
with a considerable amount of           
variability and an occasional somewhat  
long life history with successive       
stages1 there is also an essential      
constancy4 ,a systematic classification 
has been made which is becoming more or 
less satisfactory4 ,we are constantly   

learning more and more of the           
characters1 so that they can be         
recognised in different places by       
different observers4 ,it is the         
conviction of all who work with bacteria
 that1 in spite of the difficulties1 it 
is only a matter of time when we shall  
have a classification and description of
 bacteria so complete as to characterize
 the different species accurately4      
,even with our present incomplete       
knowledge of what characterizes a       
species1 it is necessary to use some    
names4 ,bacteria are commonly given a   
generic name based upon their           
microscopic appearance4 ,there are only 
a few of these names4 ,micrococcus1     
,streptococcus1 ,staphylococcus1        
,sarcina1 ,bacterium1 ,bacillus1        
,spirillum1 are all the names in common 
use applying to the ordinary bacteria4  
,there are a few others less commonly   
used4 ,to this generic name a specific  
name is commonly added1 based upon some 
physiological character4 ,for example1  

,bacillus typhosus is the name given to 
the bacillus which causes typhoid fever4
 ,such names are of great use when the  
species is a common and well-known one1 
but of doubtful value for less-known    
species ,it frequently happens that a   
bacteriologist makes a study of the     
bacteria found in a certain locality1   
and obtains thus a long list of species 
hitherto unknown4 ,in these cases it is 
common simply to number these species   
rather than name them4 ,this method is  
frequently advisable1 since the         
bacteriologist can seldom hunt up all   
bacteriological literature with         
sufficient accuracy to determine whether
 some other bacteriologist may not have 
found the same species in an entirely   
different locality4 ,one bacteriologist1
 for example1 finds some seventy        
different species of bacteria in        
different cheeses4 ,he studies them     
enough for his own purposes1 but not    
sufficiently to determine whether some  
other person may not have found the same

 species perhaps in milk or water4 ,he  
therefore simply numbers them--a method 
which conveys no suggestion as to       
whether they may be new species or not4 
,this method avoids the giving of       
separate names to the same species found
 by different observers1 and it is hoped
 that gradually accumulating knowledge  
will in time group together the forms   
which are really identical1 but which   
have been described by different        
observers4  ,,where ,,bacteria ,,are    
,,found4  ,there are no other plants or 
animals so universally found in ,nature 
as the bacteria4 ,it is this universal  
presence1 together with their great     
powers of multiplication1 which renders 
them of so much importance in ,nature4  
,they exist almost everywhere on the    
surface of the earth4 ,they are in the  
soil1 especially at its surface4 ,they  
do not extend to very great depths of   
soil1 however1 few existing below four  
feet of soil4 ,at the surface they are  
very abundant1 especially if the soil is

 moist and full of organic material4    
,the number may range from a few hundred
 to one hundred millions per gramme4    
,footnote3 ,one gramme is fifteen       
grains4 ,the soil bacteria vary also in 
species1 some two-score different       
species having been described as common 
in soil4 ,they are in all bodies of     
water1 both at the surface and below it4
 ,they are found at considerable depths 
in the ocean4 ,all bodies of fresh water
 contain them1 and all sediments in such
 bodies of water are filled with        
bacteria4 ,they are in streams of       
running water in even greater quantity  
than in standing water4 ,this is simply 
because running streams are being       
constantly supplied with water which has
 been washing the surface of the country
 and thus carrying off all surface      
accumulations4 ,lakes or reservoirs1    
however1 by standing quiet allow the    
bacteria to settle to the bottom1 and   
the water thus gets somewhat purified4  
,they are in the air1 especially in     

regions of habitation4 ,their numbers   
are greatest near the surface of the    
ground1 and decrease in the upper strata
 of air4 ,anything which tends to raise 
dust increases the number of bacteria in
 the air greatly1 and the dust and      
emanations from the clothes of people   
crowded in a close room fill the air    
with bacteria in very great numbers4    
,they are found in excessive abundance  
in every bit of decaying matter wherever
 it may be4 ,manure heaps1 dead bodies  
of animals1 decaying trees1 filth and   
slime and muck everywhere are filled    
with them1 for it is in such places that
 they find their best nourishment4 ,the 
bodies of animals contain them in the   
mouth1 stomach1 and intestine in great  
numbers1 and this is1 of course1 equally
 true of man4 ,on the surface of the    
body they cling in great quantity2      
attached to the clothes1 under the      
finger nails1 among the hairs1 in every 
possible crevice or hiding place in the 
skin1 and in all secretions4 ,they do   

not1 however1 occur in the tissues of a 
healthy individual1 either in the blood1
 muscle1 gland1 or any other organ4     
,secretions1 such as milk1 urine1 etc41 
always contain them1 however1 since the 
bacteria do exist in the ducts of the   
glands which conduct the secretions to  
the exterior1 and thus1 while the       
bacteria are never in the healthy gland 
itself1 they always succeed in          
contaminating the secretion as it passes
 to the exterior4 ,not only higher      
animals1 but the lower animals also have
 their bodies more or less covered with 
bacteria4 ,flies have them on their     
feet1 bees among their hairs1 etc4  ,in 
short1 wherever on the face of ,nature  
there is a lodging place for dust there 
will be found bacteria4 ,in most of     
these localities they are dormant1 or at
 least growing only a little4 ,the      
bacteria clinging to the dry hair can   
grow but little1 if at all1 and those in
 pure water multiply very little4 ,when 
dried as dust they are entirely dormant4

 ,but each individual bacterium or spore
 has the potential power of             
multiplication already noticed1 and as  
soon as it by accident falls upon a     
place where there is food and moisture  
it will begin to multiply4 ,everywhere  
in ,nature1 then1 exists this group of  
organisms with its almost inconceivable 
power of multiplication1 but a power    
held in check by lack of food4 ,furnish 
them with food and their potential      
powers become actual4 ,such food is     
provided by the dead bodies of animals  
or plants1 or by animal secretions1 or  
from various other sources4 ,the        
bacteria which are fortunate enough to  
get furnished with such food material   
continue to feed upon it until the food 
supply is exhausted or their growth is  
checked in some other way4 ,they may be 
regarded1 therefore1 as a constant and  
universal power usually held in check4  
,with their universal presence and their
 powers of producing chemical changes in
 food material1 they are ever ready to  

produce changes in the face of ,nature1 
and to these changes we will now turn4  
,,chapter ,,ii4  ,,miscellaneous ,,use  
,,of ,,bacteria ,,in ,,the ,,arts4      
,the foods upon which bacteria live are 
in endless variety1 almost every product
 of animal or vegetable life serving to 
supply their needs4 ,some species appear
 to require somewhat definite kinds of  
food1 and have therefore rather narrow  
conditions of life1 but the majority may
 live upon a great variety of organic   
compounds4 ,as they consume the material
 which serves them as food they produce 
chemical changes therein4 ,these changes
 are largely of a nature that the       
chemist knows as decomposition changes4 
,by this is meant that the bacteria1    
seizing hold of ingredients which       
constitute their food1 break them to    
pieces chemically4 ,the molecule of the 
original food matter is split into      
simpler molecules1 and the food is thus 
changed in its chemical nature4 ,as a   
result1 the compounds which appear in   

the decomposing solution are commonly   
simpler than the original food          
molecules4 ,such products are in general
 called decomposition products1 or      
sometimes cleavage products4 ,sometimes1
 however1 the bacteria have1 in addition
 to their power of pulling their food to
 pieces1 a further power of building    
other compounds out of the fragments1   
thus building up as well as pulling     
down4 ,but1 however they do it1 bacteria
 when growing in any food material have 
the power of giving rise to numerous    
products which did not exist in the food
 mass before4 ,because of their         
extraordinary powers of reproduction    
they are capable of producing these     
changes very rapidly and can give rise  
in a short time to large amounts of the 
peculiar products of their growth4  ,it 
is to these powers of producing chemical
 changes in their food that bacteria owe
 all their importance in the world4     
,their power of chemically destroying   
the food products is in itself of no    

little importance1 but the products     
which arise as the result of this series
 of chemical changes are of an          
importance in the world which we are    
only just beginning to appreciate4 ,in  
our attempt to outline the agency which 
bacteria play in our industries and in  
natural processes as well1 we shall     
notice that they are sometimes of value 
simply for their power of producing     
decomposition2 but their greatest value 
lies in the fact that they are important
 agents because of the products of their
 life4  ,we may notice1 in the first    
place1 that in the arts there are       
several industries which may properly be
 classed together as maceration         
industries1 all of which are based upon 
the decomposition powers of bacteria4   
,hardly any animal or vegetable         
substance is able to resist their       
softening influence1 and the artisan    
relies upon this power in several       
different directions4  ,,benefits       
,,derived ,,from ,,powers ,,of          

,,decomposition4  ,linen4--,linen       
consists of certain woody fibres of the 
stem of the flax4 ,the flax stem is not 
made up entirely of the valuable fibres1
 but largely of more brittle wood       
fibres1 which are of no use4 ,the       
valuable fibres are1 however1 closely   
united with the wood and with each other
 in such an intimate fashion that it is 
impossible to separate them by any      
mechanical means4 ,the whole cellular   
substance of the stem is bound together 
by some cementing materials which hold  
it in a compact mass1 probably a salt of
 calcium and pectinic acid4 ,the art of 
preparing flax is a process of getting  
rid of the worthless wood fibres and    
preserving the valuable1 longer1        
tougher1 and more valuable fibres1 which
 are then made into linen4 ,but to      
separate them it is necessary first to  
soften the whole tissue4 ,this is always
 done through the aid of bacteria4 ,the 
flax stems1 after proper preparation1   
are exposed to the action of moisture   

and heat1 which soon develops a rapid   
bacterial growth4 ,sometimes this is    
done by simply exposing the flax to the 
dew and rain and allowing it to lie thus
 exposed for some time4 ,by another     
process the stems are completely        
immersed in water and allowed to remain 
for ten to fourteen days4 ,by a third   
process the water in which the flax is  
immersed is heated from #ge degrees to  
#ij degrees ,f41 with the addition of   
certain chemicals1 for some fifty to    
sixty hours4 ,in all cases the effect is
 the same4 ,the moisture and the heat   
cause a growth of bacteria which        
proceeds with more or less rapidity     
according to the temperature and other  
conditions4 ,a putrefactive fermentation
 is thus set up which softens the gummy 
substance holding the fibres together4  
,the process is known as retting1 and   
after it is completed the fibres are    
easily isolated from each other4 ,a     
purely mechanical process now easily    
separates the valuable fibres from the  

wood fibres4 ,the whole process is a    
typical fermentation4 ,a disagreeable   
odour arises from the fermenting flax1  
and the liquid after the fermentation is
 filled with products which make        
valuable manure4 ,the process has not   
been scientifically studied until very  
recently4 ,the bacillus which produces  
the retting is known now1 however1 and  
it has been shown that the retting is a 
process of decomposition of the pectin  
cement4 ,no method of separating the    
linen fibres in the flax from the wood  
fibres has yet been devised which       
dispenses with the aid of bacteria4     
,jute and ,hemp4--,almost exactly the   
same use is made of bacterial action in 
the manufacture of jute und hemp4 ,the  
commercial aspect of the jute industry  
has grown to be a large one1 involving  
many millions of dollars4 ,like linen1  
jute is a fibre of the inner bark of a  
plant1 and is mixed in the bark with a  
mass of other useless fibrous material4 
,as in the case of linen1 a fermentation

 by bacteria is depended upon as a means
 of softening the material so that the  
fibres can be disassociated4 ,the       
process is called retting1 as in the    
linen manufacture4 ,the details of the  
process are somewhat different4 ,the    
jute is commonly fermented in tanks of  
stagnant water1 although sometimes it is
 allowed to soak in river water for a   
sufficient length of time to produce the
 softening4 ,after the fermentation is  
thus started the jute fibre is separated
 from the wood1 and is of a sufficient  
flexibility and toughness to be woven   
into sacking1 carpets1 curtains1 table  
covers1 and other coarse cloth4         
,practically the same method is used in 
separating the tough fibres of the hemp4
 ,the hemp plant contains some long     
flexible fibres with others of no value1
 and bacterial fermentation is relied   
upon to soften the tissues so that they 
may be separated4  ,cocoanut fibre1 a   
somewhat similar material is obtained   
from the husk of the cocoanut by the    

same means4 ,the unripened husk is      
allowed to steep and ferment in water   
for a long time1 six months or a year   
being required4 ,by this time the husk  
has become so softened that it can be   
beaten until the fibres separate and can
 be removed4 ,they are subsequently made
 into a number of coarse articles1      
especially valuable for their toughness4
 ,door mats1 brushes1 ships' fenders1   
etc41 are illustrations of the sort of  
articles made from them4  ,in each of   
these processes the fermentation must   
have a tendency to soften the desired   
fibres as well as the connecting        
substance4 ,putrefaction attacks all    
kinds of vegetable tissue1 and if this  
retting continues too long the desired  
fibre is decidedly injured by the       
softening effect of the fermentation4   
,it is quite probable that1 even as     
commonly carried on1 the fermentation   
has some slight injurious effect upon   
the fibre1 and that if some purely      
mechanical means could be devised for   

separating the fibre from the wood it   
would produce a better material4 ,but   
such mechanical means has not been      
devised1 and at present a putrefactive  
fermentation appears to be the only     
practical method of separating the      
fibres4  ,sponges4--,a somewhat similar 
use is made of bacteria in the          
commercial preparation of sponges4 ,the 
sponge of commerce is simply the fibrous
 skeleton of a marine animal4 ,when it  
is alive this skeleton is completely    
filled with the softer parts of the     
animal1 and to fit the sponge for use   
this softer organic material must be got
 rid of4 ,it is easily accomplished by  
rotting4 ,the fresh sponges are allowed 
to stand in the warm sun and very       
rapidly decay4 ,bacteria make their way 
into the sponge and thoroughly decompose
 the soft tissues4 ,after a short       
putrefaction of this sort the softened  
organic matter can be easily washed out 
of the skeleton and leave the clean     
fibre ready for market4  ,leather       

preparation4--,the tanning of leather is
 a purely chemical process1 and in some 
processes the whole operation of        
preparing the leather is a chemical one4
 ,in others1 however1 especially in     
,america1 bacteria are brought into     
action at one stage4 ,the dried hide    
which comes to the tannery must first   
have the hair removed together with the 
outer skin4 ,the hide for this purpose  
must be moistened and softened4 ,in some
 tanneries this is done by steeping it  
in chemicals4 ,in others1 however1 it is
 put into water and slightly heated     
until fermentation arises4 ,the         
fermentation softens it so that the     
outer skin can be easily removed with a 
knife1 and the removal of hair is       
accomplished at the same time4          
,bacterial putrefaction in the tannery  
is thus an assistance in preparing the  
skin for the tanning proper4 ,even in   
the subsequent tanning a bacterial      
fermentation appears to play a part1 but
 little is yet known in regard to it4   

,maceration of skeletons4--,the making  
of skeletons for museums and anatomical 
instruction in general is no very great 
industry1 and yet it is one of          
importance4 ,in the making of skeletons 
the process of maceration is commonly   
used as an aid4 ,the maceration consists
 simply in allowing the skeleton to soak
 in water for a day or two after        
cleaning away the bulk of the muscles4  
,the putrefaction that arises softens   
the connective tissues so much that the 
bones may be readily cleaned of flesh4  
,citric acid4--,bacterial fermentation  
is employed also in the ordinary        
preparation of citric acid4 ,the acid is
 made chiefly from the juice of the     
lemon4 ,the juice is pressed from the   
fruit and then allowed to ferment4 ,the 
fermentation aids in separating a       
mucilaginous mass and making it thus    
possible to obtain the citric acid in a 
purer condition4 ,the action is probably
 similar to the maceration processes    
described above1 although it has not as 

yet been studied by bacteriologists4    
,,benefits ,,derived ,,from ,,the       
,,products ,,of ,,bacterial ,,life4     
,while bacteria thus play a part in our 
industries simply from their power of   
producing decomposition1 it is primarily
 because of the products of their action
 that they are of value4 ,wherever      
bacteria seize hold of organic matter   
and feed upon it1 there are certain to  
be developed new chemical compounds1    
resulting largely from decomposition1   
but partly also from constructive       
processes4 ,these new compounds are of  
great variety4 ,different species of    
bacteria do not by any means produce the
 same compounds even when growing in and
 decomposing the same food material4    
,moreover1 the same species of bacteria 
may give rise to different products when
 growing in different food materials4   
,some of the compounds produced by such 
processes are poisonous1 others are     
harmless4 ,some are gaseous1 others are 
liquids4 ,some have peculiar odours1 as 

may be recognised from the smell arising
 from a bit of decaying meat4 ,others   
have peculiar tastes1 as may be realized
 in the gamy taste of meat which is in  
the incipient stages of putrefaction4   
,by purely empirical means mankind has  
learned methods of encouraging the      
development of some of these products1  
and is to-day making practical use of   
this power1 possessed by bacteria1 of   
furnishing desired chemical compounds4  
,industries involving the investment of 
hundreds of millions of dollars are     
founded upon the products of bacterial  
life1 and they have a far more important
 relation to our everyday life than is  
commonly imagined4 ,in many cases the   
artisan who is dependent upon this      
action of microscopic life is unaware of
 the fact4 ,his processes are those     
which experience has taught produce     
desired results1 but1 nevertheless1 his 
dependence upon bacteria is none the    
less fundamental4  ,,bacteria ,,in ,,the
 ,,fermentative ,,industries4  ,we may  

notice1 first1 several miscellaneous    
instances of the application of bacteria
 to various fermentative industries     
where their aid is of more or less value
 to man4 ,in some of the examples to be 
mentioned the influence of bacteria is  
profound and fundamental1 while in      
others it is only incidental4 ,the      
fermentative industries of civilization 
are gigantic in extent1 and have come to
 be an important factor in modern       
civilized life4 ,the large part of the  
fermentation is based upon the growth of
 a class of microscopic plants which we 
call yeasts4 ,bacteria and yeasts are   
both microscopic plants1 and perhaps    
somewhat closely related to each other4 
,the botanist finds a difference between
 them1 based upon their method of       
multiplication1 and therefore places    
them in different classes 7,fig4 #b1    
page #ai74 ,in their general power of   
producing chemical changes in their food
 products1 yeasts agree closely with    
bacteria1 though the kinds of chemical  

changes are different4 ,the whole of the
 great fermentative industries1 in which
 are invested hundreds of millions of   
dollars1 is based upon chemical         
decompositions produced by microscopic  
plants4 ,in the great part of commercial
 fermentations alcohol is the product   
desired1 and alcohol1 though it is      
sometimes produced by bacteria1 is in   
commercial quantities produced only by  
yeasts4 ,hence it is that1 although the 
fermentations produced by bacteria are  
more common in ,nature than those       
produced by yeasts and give rise to a   
much larger number of decomposition     
products1 still their commercial aspect 
is decidedly less important than that of
 yeasts4 ,nevertheless1 bacteria are not
 without their importance in the        
ordinary fermentative processes4        
,although they are of no importance as  
aids in the common fermentative         
processes1 they are not infrequently the
 cause of much trouble4 ,in the         
fermentation of malt to produce beer1 or

 grape juice to produce wine1 it is the 
desire of the brewer and vintner to have
 this fermentation produced by pure     
yeasts1 unmixed with bacteria4 ,if the  
yeast is pure the fermentation is       
uniform and successful4 ,but the brewer 
and vintner have long known that the    
fermentation is frequently interfered   
with by irregularities4 ,the troubles   
which arise have long been known1 but   
the bacteriologist has finally          
discovered their cause1 and in general  
their remedy4 ,the cause of the chief   
troubles which arise in the fermentation
 is the presence of contaminating       
bacteria among the yeasts4 ,these       
bacteria have been more or less         
carefully studied by bacteriologists1   
and their effect upon the beer or wine  
determined4 ,some of them produce acid  
and render the products sour2 others    
make them bitter2 others1 again1 produce
 a slimy material which makes the wine  
or beer ropy4 ,something like a score of
 bacteria species have been found liable

 to occur in the fermenting material and
 destroy the value of the product of    
both the wine maker and the beer brewer4
 ,the species of bacteria which infect  
and injure wine are different from those
 which infect and injure beer4 ,they are
 ever present as possibilities in the   
great alcoholic fermentations4 ,they are
 dangers which must be guarded against4 
,in former years the troubles from these
 sources were much greater than they are
 at present4 ,since it has been         
demonstrated that the different         
imperfections in the fermentative       
process are due to bacterial impurities1
 commonly in the yeasts which are used  
to produce the fermentation1 methods of 
avoiding them are readily devised4      
,to-day the vintner has ready command of
 processes for avoiding the troubles    
which arise from bacteria1 and the      
brewer is always provided with a        
microscope to show him the presence or  
absence of the contaminating bacteria4  
,while1 then1 the alcoholic             

fermentations are not dependent upon    
bacteria1 the proper management of these
 fermentations requires a knowledge of  
their habits and characters4  ,there are
 certain other fermentative processes of
 more or less importance in their       
commercial aspects1 which are directly  
dependent upon bacterial action1 ,some  
of them we should unhesitatingly look   
upon as fermentations1 while others     
would hardly be thought of as belonging 
to the fermentation industries4         
,,vinegar4  ,the commercial importance  
of the manufacture of vinegar1 though   
large1 does not1 of course1 compare in  
extent with that of the alcoholic       
fermentations4 ,vinegar is a weak       
solution of acetic acid1 together with  
various other ingredients which have    
come from the materials furnishing the  
acid4 ,in the manufacture of vinegar1   
alcohol is always used as the source of 
the acetic acid4 ,the production of     
acetic acid from alcohol is a simple    
oxidation4 ,the equation ,c#b;,h#f,o    

,o#b  ,c#b;,h#d,o#b  ,h#b,o shows the   
chemical change that occurs4 ,this      
oxidation can be brought about by purely
 chemical means4 ,while alcohol will not
 readily unite with oxygen under common 
conditions1 if the alcohol is allowed to
 pass over a bit of platinum sponge the 
union readily occurs and acetic acid    
results4 ,this method of acetic-acid    
production is possible experimentally1  
but is impracticable on any large scale4
 ,in the ordinary manufacture of vinegar
 the oxidation is a true fermentation1  
and brought about by the growth of      
bacteria4  ,in the commercial           
manufacture of vinegar several different
 weak alcoholic solutions are used4 ,the
 most common of these are fermented     
malt1 weak wine1 cider1 and sometimes a 
weak solution of spirit to which is     
added sugar and malt4 ,if these         
solutions are allowed to stand for a    
time in contact with air1 they slowly   
turn sour by the gradual conversion of  
the alcohol into acetic acid4 ,at the   

close of the process practically all of 
the alcohol has disappeared4            
,ordinarily1 however1 not all of it has 
been converted into acetic acid1 for the
 oxidation does not all stop at this    
step4 ,as the oxidation goes on1 some of
 the acid is oxidized into carbonic     
dioxide1 which is1 of course1 dissipated
 at once into the air1 and if the       
process is allowed to continue unchecked
 for a long enough period much of the   
acetic acid will be lost in this way4   
,the oxidation of the alcohol in all    
commercial production of vinegar is     
brought about by the growth of bacteria 
in the liquid4 ,when the vinegar        
production is going on properly1 there  
is formed on the top of the liquid a    
dense felted mass known as the mother of
 vinegar4 ,this mass proves to be made  
of bacteria which have the power of     
absorbing oxygen from the air1 or1 at   
all events1 of causing the alcohol to   
unite with oxygen4 ,it was at first     
thought that a single species of        

bacterium was thus the cause of the     
oxidation of alcohol1 and this was named
 ,mycoderma aceti4 ,but further study   
has shown that several have the power1  
and that even in the commercial         
manufacture of vinegar several species  
play a part 7,fig4 #ah71 although the   
different species are not yet very      
thoroughly studied4 ,each appears to act
 best under different conditions4 ,some 
of them act slowly1 and others rapidly1 
the slow- growing species appearing to  
produce the larger amount of acid in the
 end4 ,after the amount of acetic acid  
reaches a certain percentage1 the       
bacteria are unable to produce more1    
even though there be alcohol still left 
unoxidized4 ,a percentage as high as    
fourteen per cent1 commonly destroys all
 their power of growth4 ,the production 
of the acid is wholly dependent upon the
 growth of the bacteria1 and the secret 
of the successful vinegar manufacture is
 the skilful manipulation of these      
bacteria so as to keep them in the      

purest condition and to give them the   
best opportunity for growth4  ,one      
method of vinegar manufacture which is  
quite rapid is carried on in a slightly 
different manner4 ,a tall cylindrical   
chamber is filled with wood shavings1   
and a weak solution of alcohol is       
allowed to trickle slowly through it4   
,the liquid after passing over the      
shavings comes out after a number of    
hours well charged with acetic acid4    
,this process at first sight appears to 
be a purely chemical one1 and reminds us
 of the oxidation which occurs when     
alcohol is allowed to pass over a       
platinum sponge4 ,it has been claimed1  
indeed1 that this is a chemical         
oxidation in which bacteria play no     
part4 ,but this appears to be an error4 
,it is always found necessary in this   
method to start the process by pouring  
upon the shavings some warm vinegar4    
,unless in this way the shavings become 
charged with the vinegar-holding        
bacteria the alcohol will not undergo   

oxidation during its passage over them1 
and after the bacteria thus introduced  
have grown enough to coat the shavings  
thoroughly the acetic-acid production is
 much more rapid than at first4 ,if     
vinegar is allowed to trickle slowly    
down a suspended string1 so that its    
bacteria may distribute themselves      
through the string1 and then alcohol be 
allowed to trickle over it in the same  
way1 the oxidation takes place and      
acetic acid is formed4 ,from the        
accumulation of such facts it has come  
to be recognised that all processes for 
the commercial manufacture of vinegar   
depend upon the action of bacteria4     
,while the oxidation of alcohol into    
acetic acid may take place by purely    
chemical means1 these processes are not 
practical on a large scale1 and vinegar 
manufacturers everywhere depend upon    
bacteria as their agents in producing   
the oxidation4 ,these bacteria1 several 
species in all1 feed upon the           
nitrogenous matter in the fermenting    

mass and produce the desired change in  
the alcohol4  ,this vinegar fermentation
 is subject to certain irregularities1  
and the vinegar manufacturers can not   
always depend upon its occurring in a   
satisfactory manner4 ,just as in        
brewing1 so here1 contaminating bacteria
 sometimes find their way into the      
fermenting mass and interfere with its  
normal course4 ,in particular1 the      
flavour of the vinegar is liable to     
suffer from such causes4 ,as yet our    
vinegar manufacturers have not applied  
to acetic fermentation the same         
principle which has been so successful  
in brewing--namely1 the use1 as a       
starter of the fermentation1 of a pure  
culture of the proper species of        
bacteria4 ,this has been done           
experimentally and proves to be         
feasible4 ,in practice1 however1 vinegar
 makers find that simpler methods of    
obtaining a starter--by means of which  
they procure a culture nearly though not
 absolutely pure--are perfectly         

satisfactory4 ,it is uncertain whether  
really pure cultures will ever be used  
in this industry4  ,,lactic ,,acid4     
,the manufacture of lactic acid is an   
industry of less extent than that of    
acetic acid1 and yet it is one which has
 some considerable commercial           
importance4 ,lactic acid is used in no  
large quantity1 although it is of some  
value as a medicine and in the arts4    
,for its production we are wholly       
dependent upon bacteria4 ,it is this    
acid which1 as we shall see1 is produced
 in the ordinary souring of milk1 and a 
large number of species of bacteria are 
capable of producing the acid from milk 
sugar4 ,any sample of sour milk may     
therefore always be depended upon to    
contain plenty of lactic organisms4 ,in 
its manufacture for commercial purposes 
milk is sometimes used as a source1 but 
more commonly other substances4         
,sometimes a mixture of cane sugar and  
tartaric acid is used4 ,to start the    
fermentation the mixture is inoculated  

with a mass of sour milk or decaying    
cheese1 or both1 such a mixture always  
containing lactic organisms4 ,to be     
sure1 it also contains many other       
bacteria which have different effects1  
but the acid producers are always so    
abundant and grow so vigorously that the
 lactic fermentation occurs in spite of 
all other bacteria4 ,here also there is 
a possibility of an improvement in the  
process by the use of pure cultures of  
lactic organisms4 ,up to the present1   
however1 there has been no application  
of such methods4 ,the commercial aspects
 of the industry are not upon a         
sufficiently large scale to call for    
much in this direction4  ,at the present
 time the only method we have for the   
manufacture of lactic acid is dependent 
upon bacteria4 ,chemical processes for  
its manufacture are known1 but not      
employed commercially4 ,there are       
several different kinds of lactic acid4 
,they differ from each other in the     
relations of the atoms within their     

molecule1 and in their relation to      
polarized light1 some forms rotating the
 plane of polarized light to the right1 
others to the left1 while others are    
inactive in this respect4 ,all the types
 are produced by fermentation processes1
 different species of bacteria having   
powers of producing the different types4
  ,,butyric ,,acid4  ,butyric acid is   
another acid for which we are chiefly   
dependent upon bacteria4 ,this acid is  
of no very great importance1 and its    
manufacture can hardly be called an     
industry2 still it is to a certain      
extent made1 and is an article of       
commerce4 ,it is an acid that can be    
manufactured by chemical means1 but1 as 
in the case of the last two acids1 its  
commercial manufacture is based upon    
bacterial action4 ,quite a number of    
species of bacteria can produce butyric 
acid1 and they produce it from a variety
 of different sources4 ,butyric acid is 
a common ingredient in old milk and in  
butter1 and its formation by bacteria   

was historically one of the first       
bacterial fermentations to be clearly   
understood4 ,it can be produced also in 
various sugar and starchy solutions4    
,glycerine may also undergo a butyric   
fermentation4 ,the presence of this acid
 is occasionally troublesome1 since it  
is one of the factors in the rancidity  
of butter and other similar materials4  
,,indigo ,,preparation4  ,the           
preparation of indigo from the indigo   
plant is a fermentative process brought 
about by a specific bacterium4 ,the     
leaves of the plant are immersed in     
water in a large vat1 and a rapid       
fermentation arises4 ,as a result of the
 fermentation the part of the plant     
which is the basis of the indigo is     
separated from the leaves and dissolved 
in the water2 and as a second feature of
 the fermentation the soluble material  
is changed in its chemical nature into  
indigo proper4 ,as this change occurs   
the characteristic blue colour is       
developed1 and the material is rendered 

insoluble in water4 ,it therefore makes 
its appearance as a blue mass separated 
from the water1 and is then removed as  
indigo4  ,of the nature of the process  
we as yet know very little4 ,that it is 
a fermentation is certain1 and it has   
been proved that it is produced by a    
definite species of bacterium which     
occurs on the indigo leaves4 ,if the    
sterilized leaves are placed in sterile 
water no fermentation occurs and no     
indigo is formed4 ,if1 however1 some of 
the specific bacteria are added to the  
mass the fermentation soon begins and   
the blue colour of the indigo makes its 
appearance4 ,it is plain1 therefore1    
that indigo is a product of bacterial   
fermentation1 and commonly due to a     
single definite species of bacterium4   
,of the details of the formation1       
however1 we as yet know little1 and no  
practical application of the facts have 
yet been made4  ,,bacteria ,,in         
,,tobacco ,,curing4  ,a fermentative    
process of quite a different nature1 but

 of immense commercial value1 is found  
in the preparation of tobacco4 ,the     
process by which tobacco is prepared is 
a long and somewhat complicated one1    
consisting of a number of different     
stages4 ,the tobacco1 after being first 
dried in a careful manner1 is           
subsequently allowed to absorb moisture 
from the atmosphere1 and is then placed 
in large heaps to undergo a further     
change4 ,this process appears to be a   
fermentation1 for the temperature of the
 mass rises rapidly1 and every          
indication of a fermentative action is  
seen4 ,the tobacco in these heaps is    
changed occasionally1 the heap being    
thrown down and built up again in such a
 way that the portion which was first at
 the bottom comes to the top1 and in    
this way all parts of the heap may      
become equally affected by the process4 
,after this process the tobacco is sent 
to the different manufacturers1 who     
finish the process of curing4 ,the      
further treatment it receives varies    

widely according to the desired product1
 whether for smoking or for snuff1 etc4 
,in all cases1 however1 fermentations   
play a prominent part4 ,sometimes the   
leaves are directly inoculated with     
fermenting material4 ,in the preparation
 of snuff the details of the process are
 more complicated than in the           
preparation of smoking tobacco4 ,the    
tobacco1 after being ground and mixed   
with certain ingredients1 is allowed to 
undergo a fermentation which lasts for  
weeks1 and indeed for months4 ,in the   
different methods of preparing snuff the
 fermentations take place in different  
ways1 and sometimes the tobacco is      
subjected to two or three different     
fermentative actions4 ,the result of the
 whole is the slow preparation of the   
commercial product4 ,it is during the   
final fermentative processes that the   
peculiar colour and flavour of the snuff
 are developed1 and it is during the    
fermentation of the leaves of the       
smoking tobacco--either the original    

fermentation or the subsequent ones--   
that the special flavours and aromas of 
tobacco are produced4  ,it can not be   
claimed for a moment that these changes 
by which the tobacco is cured and       
finally brought to a marketable         
condition are due wholly to bacteria4   
,there is no question that chemical and 
physical phenomena play an important    
part in them4 ,nevertheless1 from the   
moment when the tobacco is cut in the   
fields until the time it is ready for   
market the curing is very intimately    
associated with bacteria and            
fermentative organisms in general4 ,some
 of these processes are wholly brought  
about by bacterial life2 in others the  
micro-organisms aid the process1 though 
they perhaps can not be regarded as the 
sole agents4  ,at the outset the tobacco
 producer has to contend with a number  
of micro-organisms which may produce    
diseases in his tobacco4 ,during the    
drying process1 if the temperature or   
the amount of moisture or the access of 

air is not kept in a proper condition1  
various troubles arise and various      
diseases make their appearance1 which   
either injure or ruin the value of the  
product4 ,these appear to be produced by
 micro-organisms of different sorts4    
,during the fermentation which follows  
the drying the producer has to contend  
with micro-organisms that are           
troublesome to him2 for unless the      
phenomena are properly regulated the    
fermentation that occurs produces       
effects upon the tobacco which ruin its 
character4 ,from the time the tobacco is
 cut until the final stage in the curing
 the persons engaged in preparing it for
 market must be on a constant watch to  
prevent the growth within it of         
undesirable organisms4 ,the preparation 
of tobacco is for this reason a delicate
 operation1 and one that will be very   
likely to fail unless the greatest care 
is taken4 ,in the several fermentative  
processes which occur in the preparation
 there is no question that              

micro-organisms aid the tobacco producer
 and manufacturer4 ,bacteria produce the
 first fermentation that follows the    
drying1 and it is these organisms too1  
in large measure1 that give rise to all 
the subsequent fermentations1 although  
seemingly in some cases purely chemical 
processes materially aid4 ,now the      
special quality of the tobacco is in    
part dependent upon the peculiar type of
 fermentation which occurs in one or    
another of these fermenting actions4 ,it
 is the fermentation that gives rise to 
the peculiar flavour and to the aroma of
 the different grades of tobacco4       
,inasmuch as the various flavours which 
characterize tobacco of different grades
 are developed1 at least to a large     
extent1 during the fermentation         
processes1 it is a natural supposition  
that the different qualities of the     
tobacco1 so far as concerns flavour1 are
 due to the different types of          
fermentation4 ,the number of species of 
bacteria which are found upon the       

tobacco leaves in the various stages of 
its preparation is quite large1 and from
 what we have already learned it is     
inevitable that the different kinds of  
bacteria will produce different results 
in the fermenting process4 ,it would    
seem natural1 therefore1 to assume that 
the different flavours of different     
grades may not unlikely be due to the   
fact that the tobacco in the different  
cases has been fermented under the      
influence of different kinds of         
bacteria4  ,nor is this simply a matter 
of inference4 ,to a certain extent      
experimental evidence has borne out the 
conclusion1 and has given at least a    
slight indication of practical results  
in the future4 ,acting upon the         
suggestion that the difference between  
the high grades of tobacco and the      
poorer grades is due to the character of
 the bacteria that produce the          
fermentation1 certain bacteriologists   
have attempted to obtain from a high    
quality of tobacco the species of       

bacteria which are infesting it4 ,these 
bacteria have then been cultivated by   
bacteriological methods and used in     
experiments for the fermentation of     
tobacco4 ,if it is true that the flavour
 of high grade tobacco is in large      
measure1 or even in part1 due to the    
action of the peculiar microbes from the
 soil where it grows1 it ought to be    
possible to produce similar flavours in 
the leaves of tobacco grown in other    
localities1 if the fermentation of the  
leaves is carried on by means of the    
pure cultures of bacteria obtained from 
the high grade tobacco4 ,not very much  
has been done or is known in this       
connection as yet4 ,two bacteriologists 
have experimented independently in      
fermenting tobacco leaves by the action 
of pure cultures of bacteria obtained   
from such sources4 ,each of them reports
 successful experiments4 ,each claims   
that they have been able to improve the 
quality of tobacco by inoculating the   
leaves with a pure culture of bacteria  

obtained from tobacco having high       
quality in flavour4 ,in addition to     
this1 several other bacteriologists have
 carried on experiments sufficient to   
indicate that the flavours of the       
tobacco and the character of the        
ripening may be decidedly changed by the
 use of different species of            
micro-organisms in the fermentations    
that go on during the curing processes4 
,in regard to the whole matter1 however1
 we must recognise that as yet we have  
very little knowledge4 ,the subject has 
been under investigation for only a     
short time2 and1 while considerable     
information has been derived1 this      
information is not thoroughly           
understood1 and our knowledge in regard 
to the matter is as yet in rather a     
chaotic condition4 ,it seems certain1   
however1 that the quality of tobacco is 
in large measure dependent upon the     
character of the fermentations that     
occur at different stages of the curing4
 ,it seems certain also that these      

fermentations are wholly or chiefly     
produced by microorganisms1 and that the
 character of the fermentation is in    
large measure dependent upon the species
 of micro-organisms that produce it4 ,if
 these are facts1 it would seem not     
improbable that a further study may     
produce practical results for this great
 industry4 ,the study of yeasts and the 
methods of keeping yeast from           
contaminations has revolutionised the   
brewing industry4 ,perhaps in this other
 fermentative industry1 which is of such
 great commercial extent1 the use of    
pure cultures of bacteria may in the    
future produce as great revolutions in  
methods as it has in the industry of the
 alcoholic fermentation4  ,it must not1 
however1 be inferred that the           
differences in grades of tobacco grown  
in different parts of the world are due 
solely to variations in the curing      
processes and to the types of           
fermentation4 ,there are differences in 
the texture of the leaves1 differences  

in the chemical composition of the      
tobaccoes1 which are due undoubtedly to 
the soils and the climatic conditions in
 which they grow1 and these1 of course1 
will never be affected by changing the  
character of the ferment active         
processes4 ,it is1 however1 probable    
that in so far as the flavours that     
distinguish the high and low grades of  
tobacco are due to the character of the 
fermentative processes1 they may be in  
the future1 at least to a large extent1 
controlled by the use of pure cultures  
in curing processes4 ,seemingly1 then1  
there is as great a future in the       
development of this fermentative        
industry as there has been in the past  
in the development of the fermentative  
industry associated with brewing and    
vinting4  ,,opium4  ,opium for smoking  
purposes is commonly allowed to undergo 
a curing process which lasts several    
months4 ,this appears to be somewhat    
similar to the curing of tobacco4       
,apparently it is a fermentation due to 

the growth of microorganisms4 ,the      
organisms in question are not1 however1 
bacteria in this case1 but a species of 
allied fungus4 ,the plant is a mould1   
and it is claimed that inoculation of   
the opium with cultures of this mould   
hastens the curing4  ,,troublesome      
,,fermentations4  ,before leaving this  
branch of the subject it is necessary to
 notice some of the troublesome         
fermentations which are ever interfering
 with our industries1 requiring special 
methods1 or1 indeed1 sometimes          
developing special industries to meet   
them4 ,as agents of decomposition1      
bacteria will of course be a trouble    
whenever they get into material which it
 is desired to preserve4 ,since they are
 abundant everywhere1 it is necessary to
 count upon their attacking with        
certainty any fermentable substance     
which is exposed to air and water4      
,hence they are frequently the cause of 
much trouble4 ,in the fermentative      
industries they occasionally cause an   

improper sort of fermentation to occur  
unless care is taken to prevent         
undesired species of bacteria from being
 present4 ,in vinegar making1 improper  
species of bacteria obtaining access to 
the solution give rise to undesirable   
flavours1 greatly injuring the product4 
,in tobacco curing it is very common for
 the wrong species of bacteria to gain  
access to the tobacco at some stage of  
the curing and by their growth give rise
 to various troubles4 ,it is the        
ubiquitous presence of bacteria which   
makes it impossible to preserve fruits1 
meats1 or vegetables for any length of  
time without special methods4 ,this fact
 in itself has caused the development of
 one of our most important industries4  
,canning meats or fruits consists in    
nothing more than bringing them into a  
condition in which they will be         
preserved from attack of these          
micro-organisms4 ,the method is         
extremely simple in theory4 ,it is      
nothing more than heating the material  

to be preserved to a high temperature   
and then sealing it hermetically while  
it is still hot4 ,the heat kills all the
 bacteria which may chance to be lodged 
in it1 and the hermetical sealing       
prevents other bacteria from obtaining  
access4 ,inasmuch as all organic        
decomposition is produced by bacterial  
growth1 such sterilized and sealed      
material will be preserved indefinitely 
when the operation is performed         
carefully enough4 ,the methods of       
accomplishing this with sufficient care 
are somewhat varied in different        
industries1 but they are all            
fundamentally the same4 ,it is an       
interesting fact that this method of    
preserving meats was devised in the last
 century1 before the relation of        
micro-organisms to fermentation and     
putrefaction was really suspected4 ,for 
a long time it had been in practical use
 while scientists were still disputing  
whether putrefaction could be avoided by
 preventing the access of bacteria4 ,the

 industry has1 however1 developed       
wonderfully within the last few years1  
since the principles underlying it have 
been understood4 ,this understanding has
 led to better methods of destroying    
bacterial life and to proper sealing1   
and these have of course led to greater 
success in the preservation1 until      
to-day the canning industries are among 
those which involve capital reckoned in 
the millions4  ,occasionally bacteria   
are of some value in food products4 ,the
 gamy flavour of meats is nothing more  
than incipient decomposition4 ,sauer    
,kraut is a food mass intentionally     
allowed to ferment and sour4 ,the value 
of bacteria in producing butter and     
cheese flavours is noticed elsewhere4   
,but commonly our aim must be to prevent
 the growth of bacteria in foods4 ,foods
 must be dried or cooked or kept on ice1
 or some other means adopted for        
preventing bacterial growth in them4 ,it
 is their presence that forces us to    
keep our ice box1 thus founding the ice 

business1 as well as that of the        
manufacture of refrigerators4 ,it is    
their presence1 again1 that forces us to
 smoke hams1 to salt mackerel1 to dry   
fish or other meats1 to keep pork in    
brine1 and to introduce numerous other  
details in the methods of food          
preparation and preservation4           
,,chapter ,,iii4  ,,relation ,,of       
,,bacteria ,,to ,,the ,,dairy           
,,industry4   ,dairying is one of the   
most primitive of our industries4 ,from 
the very earliest period1 ever since man
 began to keep domestic cattle1 he has  
been familiar with dairying4 ,during    
these many centuries certain methods of 
procedure have been developed which     
produce desired results4 ,these methods1
 however1 have been devised simply from 
the accumulation of experience1 with    
very little knowledge as to the reasons 
underlying them4 ,the methods of past   
centuries are1 however1 ceasing to be   
satisfactory4 ,the advance of our       
civilization during the last half       

century has seen a marked expansion in  
the extent of the dairy industry4 ,with 
this expansion has appeared the         
necessity for new methods1 and dairymen 
have for years been looking for them4   
,the last few years have been teaching  
us that the new methods are to be found 
along the line of the application of the
 discoveries of modern bacteriology4 ,we
 have been learning that the dairyman is
 more closely related to bacteria and   
their activities than almost any other  
class of persons4 ,modern dairying1     
apart from the matter of keeping the    
cow1 consists largely in trying to      
prevent bacteria from growing in milk or
 in stimulating their growth in cream1  
butter1 and cheese4 ,these chief        
products of the dairy will be considered
 separately4  ,,sources ,,of ,,bacteria 
,,in ,,milk4  ,the first fact that      
claims our attention is1 that milk at   
the time it is secreted from the udder  
of the healthy cow contains no bacteria4
 ,although bacteria are almost          

ubiquitous1 they are not found in the   
circulating fluids of healthy animals1  
and are not secreted by their glands4   
,milk when first secreted by the milk   
gland is therefore free from bacteria4  
,it has taken a long time to demonstrate
 this fact1 but it has been finally     
satisfactorily proved4 ,secondly1 it has
 been demonstrated that practically all 
of the normal changes which occur in    
milk after its secretion are caused by  
the growth of bacteria4 ,this1 too1 was 
long denied1 and for quite a number of  
years after putrefactions and           
fermentations were generally            
acknowledged to be caused by the growth 
of micro- organisms1 the changes which  
occurred in milk were excepted from the 
rule4 ,the uniformity with which milk   
will sour1 and the difficulty1 or       
seeming impossibility1 of preventing    
this change1 led to the belief that the 
souring of milk was a normal change     
characteristic of milk1 just as clotting
 is characteristic of blood4 ,this was1 

however1 eventually disproved1 and it   
was finally demonstrated that1 beyond a 
few physical changes connected with     
evaporation and a slight oxidation of   
the fat1 milk1 if kept free from        
bacteria1 will undergo no change4 ,if   
bacteria are not present1 it will remain
 sweet indefinitely4  ,but it is        
impossible to draw milk from the cow in 
such a manner that it will be free from 
bacteria except by the use of           
precautions absolutely impracticable in 
ordinary dairying4 ,as milk is commonly 
drawn1 it is sure to be contaminated by 
bacteria1 and by the time it has entered
 the milk pail it contains frequently as
 many as half a million1 or even a      
million1 bacteria in every cubic inch of
 the milk4 ,this seems almost           
incredible1 but it has been demonstrated
 in many cases and is beyond question4  
,since these bacteria are not in the    
secreted milk1 they must come from some 
external sources1 and these sources are 
the following3  ,the first in importance

 is the cow herself2 for while her milk 
when secreted is sterile1 and while     
there are no bacteria in her blood1     
nevertheless the cow is the most        
prolific source of bacterial            
contamination4 ,in the first place1 the 
milk ducts are full of them4 ,after each
 milking a little milk is always left in
 the duct1 and this furnishes an ideal  
place for bacteria to grow4 ,some       
bacteria from the air or elsewhere are  
sure to get into these ducts after the  
milking1 and they begin at once to      
multiply rapidly4 ,by the next milking  
they become very abundant in the ducts1 
and the first milk drawn washes most of 
them at once into the milk pail1 where  
they can continue their growth in the   
milk4 ,again1 the exterior of the cow's 
body contains them in abundance4 ,every 
hair1 every particle of dirt1 every bit 
of dried manure1 is a lurking place for 
millions of bacteria4 ,the hind quarters
 of a cow are commonly in a condition of
 much filth1 for the farmer rarely      

grooms his cow1 and during the milking1 
by her movements1 by the switching of   
her tail1 and by the rubbing she gets   
from the milker1 no inconsiderable      
amount of this dirt and filth is brushed
 off and falls into the milk pail ,the  
farmer understands this source of dirt  
and usually feels it necessary to strain
 the milk after the milking4 ,but the   
straining it receives through a coarse  
cloth1 while it will remove the coarser 
particles of dirt1 has no effect upon   
the bacteria1 for these pass through any
 strainer unimpeded4 ,again1 the milk   
vessels themselves contain bacteria1 for
 they are never washed absolutely clean4
 ,after the most thorough washing which 
the milk pail receives from the kitchen1
 there will always be left many bacteria
 clinging in the cracks of the tin or in
 the wood1 ready to begin to grow as    
soon as the milk once more fills the    
pail ,the milker himself contributes to 
the supply1 for he goes to the milking  
with unclean hands1 unclean clothes1 and

 not a few bacteria get from him to his 
milk pail4 ,lastly1 we find the air of  
the milking stall furnishing its quota  
of milk bacteria4 ,this source of       
bacteria is1 how ever1 not so great as  
was formerly believed4 ,that the air may
 contain many bacteria in its dust is   
certain1 and doubtless these fall in    
some quantity into the milk1 especially 
if the cattle are allowed to feed upon  
dusty hay before and during the milking4
 ,but unless the air is thus full of    
dust this source of bacteria is not very
 great1 and compared with the bacteria  
from the other sources the air bacteria 
are unimportant4  ,the milk thus gets   
filled with bacteria1 and since it      
furnishes an excellent food these       
bacteria begin at once to grow4 ,the    
milk when drawn is warm and at a        
temperature which especially stimulates 
bacterial growth4 ,they multiply with   
great rapidity1 and in the course of a  
few hours increase perhaps a            
thousandfold4 ,the numbers which may be 

found after twenty-four hours are       
sometimes inconceivable2 market milk may
 contain as many as five hundred        
millions per cubic inch2 and while this 
is a decidedly extreme number1 milk that
 is a day old will almost always contain
 many millions in each cubic inch1 the  
number depending upon the age of the    
milk and its temperature4 ,during this  
growth the bacteria have1 of course1 not
 been without their effect4 ,recognising
 as we do that bacteria are agents for  
chemical change1 we are prepared to see 
the milk undergoing some modifications  
during this rapid multiplication of     
bacteria4 ,the changes which these      
bacteria produce in the milk and its    
products are numerous1 and decidedly    
affect its value4 ,they are both        
advantageous and disadvantageous to the 
dairyman4 ,they are nuisances so far as 
concerns the milk producer1 but allies  
of the butter and cheese maker4  ,,the  
,,effect ,,of ,,bacteria ,,on ,,milk4   
,the first and most universal change    

effected in milk is its ,,souring4 ,so  
universal is this phenomenon that it is 
generally regarded as an inevitable     
change which can not be avoided1 and1 as
 already pointed out1 has in the past   
been regarded as a normal property of   
milk4 ,to-day1 however1 the phenomenon  
is well understood4 ,it is due to the   
action of certain of the milk bacteria  
upon the milk sugar which converts it   
into lactic acid1 and this acid gives   
the sour taste and curdles the milk4    
,after this acid is produced in small   
quantity its presence proves deleterious
 to the growth of the bacteria1 and     
further bacterial growth is checked4    
,after souring1 therefore1 the milk for 
some time does not ordinarily undergo   
any further changes4  ,milk souring has 
been commonly regarded as a single      
phenomenon1 alike in all cases4 ,when it
 was first studied by bacteriologists it
 was thought to be due in all cases to a
 single species of micro-organism which 
was discovered to be commonly present   

and named ,bacillus acidi lactici 7,fig4
 #ai74 ,this bacterium has certainly the
 power of souring milk rapidly1 and is  
found to be very common in dairies in   
,europe4 ,as soon as bacteriologists    
turned their attention more closely to  
the subject it was found that the       
spontaneous souring of milk was not     
always caused by the same species of    
bacterium4 ,instead of finding this     
,bacillus acidi lactici always present1 
they found that quite a number of       
different species of bacteria have the  
power of souring milk1 and are found in 
different specimens of soured milk4 ,the
 number of species of bacteria which    
have been found to sour milk has        
increased until something over a hundred
 are known to have this power4 ,these   
different species do not affect the milk
 in the same way4 ,all produce some     
acid1 but they differ in the kind and   
the amount of acid1 and especially in   
the other changes which are effected at 
the same time that the milk is soured1  

so that the resulting soured milk is    
quite variable4 ,in spite of this       
variety1 however1 the most recent work  
tends to show that the majority of cases
 of spontaneous souring of milk are     
produced by bacteria which1 though      
somewhat variable1 probably constitute a
 single species1 and are identical with 
the ,bacillus acidi lactici 7,fig4 #ai74
 ,this species1 found common in the     
dairies of ,europe1 according to recent 
investigations occurs in this country as
 well4 ,we may say1 then1 that while    
there are many species of bacteria      
infesting the dairy which can sour the  
milk1 there is one which is more common 
and more universally found than others1 
and this is the ordinary cause of milk  
souring4  ,when we study more carefully 
the effect upon the milk of the         
different species of bacteria found in  
the dairy1 we find that there is a great
 variety of changes which they produce  
when they are allowed to grow in milk4  
,the dairyman experiences many troubles 

with his milk4 ,it sometimes curdles    
without becoming acid4 ,sometimes it    
becomes bitter1 or acquires an          
unpleasant tainted taste1 or1 again1 a  
soapy taste4 ,occasionally a dairyman   
finds his milk becoming slimy1 instead  
of souring and curdling in the normal   
fashion4 ,at such times1 after a number 
of hours1 the milk becomes so slimy that
 it can be drawn into long threads4     
,such an infection proves very          
troublesome1 for many a time it persists
 in spite of all attempts made to remedy
 it4 ,again1 in other cases the milk    
will turn blue1 acquiring about the time
 it becomes sour a beautiful sky-blue   
colour4 ,or it may become red1 or       
occasionally yellow4 ,all of these      
troubles the dairyman owes to the       
presence in his milk of unusual species 
of bacteria which grow there abundantly4
  ,bacteriologists have been able to    
make out satisfactorily the connection  
of all these infections with different  
species of the bacteria4 ,a large number

 of species have been found to curdle   
milk without rendering it acid1 several 
render it bitter1 and a number produce a
 tainted and one a soapy taste4 ,a score
 or more have been found which have the 
power of rendering the milk slimy4 ,two 
different species at least have the     
power of turning the milk to sky-blue   
colour2 two or three produce red        
pigments 7,fig4 #bj71 and one or two    
have been found which produce a yellow  
colour4 ,in short1 it has been          
determined beyond question that all     
these infections1 which are more or less
 troublesome to dairymen1 are due to the
 growth of unusual bacteria in the milk4
  ,these various infections are all     
troublesome1 and indeed it may be said  
that1 so far as concerns the milk       
producer and the milk consumer1 bacteria
 are from beginning to end a source of  
trouble4 ,it is the desire of the milk  
producer to avoid them as far as        
possible--a desire which is shared also 
by everyone who has anything to do with 

milk as milk4 ,having recognised that   
the various troubles1 which occasionally
 occur even in the better class of      
dairies1 are due to bacteria1 the       
dairyman is1 at least in a measure1     
prepared to avoid them4 ,the avoiding of
 these troubles is moderately easy as   
soon as dairymen recognise the source   
from which the infectious organisms     
come1 and also the fact that low        
temperatures will in all cases remedy   
the evil to a large extent4 ,with this  
knowledge in hand the avoidance of all  
these troubles is only a question of    
care in handling the dairy4 ,it must be 
recognised that most of these           
troublesome bacteria come from some     
unusual sources of infection4 ,by       
unusual sources are meant those which   
the exercise of care will avoid4 ,it is 
true that the souring bacteria appear to
 be so universally distributed that they
 can not be avoided by any ordinary     
means4 ,but all other troublesome       
bacteria appear to be within control4   

,the milkman must remember that the     
sources of the troubles which are liable
 to arise in his milk are in some form  
of filth3 either filth on the cow1 or   
dust in the hay which is scattered      
through the barn1 or dirt on cows'      
udders1 or some other unusual and       
avoidable source4 ,these sources1 from  
what we have already noticed1 will      
always furnish the milk with bacteria2  
but under common conditions1 and when   
the cow is kept in conditions of        
ordinary cleanliness1 and frequently    
even when not cleanly1 will only furnish
 bacteria that produce the universal    
souring4 ,recognising this1 the dairyman
 at once learns that his remedies for   
the troublesome infections are          
cleanliness and low temperatures4 ,if he
 is careful to keep his milk vessels    
scrupulously clean2 if he will keep his 
cow as cleanly as he does his horse2 and
 if he will use care in and around the  
barn and dairy1 and then apply low      
temperatures to the milk1 he need never 

be disturbed by slimy or tainted milk1  
or any of these other troubles2 or he   
can remove such infections speedily     
should they once appear4 ,pure sweet    
milk is only a question of sufficient   
care4 ,but care means labour and        
expense4 ,as long as we demand cheap    
milk1 so long will we be supplied with  
milk procured under conditions of filth4
 ,but when we learn that cheap milk is  
poor milk1 and when we are willing to   
pay a little more for it1 then only may 
we expect the use of greater care in the
 handling of the milk1 resulting in a   
purer product4  ,bacteriology has       
therefore taught us that the whole      
question of the milk supply in our      
communities is one of avoiding the too  
rapid growth of bacteria4 ,these        
organisms are uniformly a nuisance to   
the milkman4 ,to avoid their evil       
influence have been designed all the    
methods of caring for the dairy and the 
barn1 all the methods of distributing   
milk in ice cars4 ,moreover1 all the    

special devices connected with the great
 industry of milk supply have for their 
foundation the attempt to avoid1 in the 
first place1 the presence of too great a
 number of bacteria1 and4 in the second 
place1 the growth of these bacteria4    
,,bacteria ,,in ,,butter ,,making4      
,,cream ,,ripening4--,passing from milk 
to butter1 we find a somewhat different 
story1 inasmuch as here bacteria are    
direct allies to the dairyman rather    
than his enemies4 ,without being aware  
of it1 butter makers have for years been
 making use of bacteria in their butter 
making and have been profiting by the   
products which the bacteria have        
furnished them4 ,cream1 as it is        
obtained from milk1 will always contain 
bacteria in large quantity1 and these   
bacteria will grow as readily in the    
cream as they will in the milk4 ,the    
butter maker seldom churns his cream    
when it is freshly obtained from the    
milk4 ,there are1 it is true1 some      
places where sweet cream butter is made 

and is in demand1 but in the majority of
 butter-consuming countries a different 
quality of butter is desired1 and the   
cream is subjected to a process known as
 ripening or souring before it is       
churned4 ,in ripening1 the cream is     
simply allowed to stand in a vat for a  
period varying from twelve hours to two 
or three days1 according to             
circumstances4 ,during this period      
certain changes take place therein4 ,the
 bacteria which were in the cream       
originally1 get an opportunity to grow1 
and by the time the ripening is complete
 they become extremely numerous4 ,as a  
result1 the character of the cream      
changes just as the milk is changed     
under similar circumstances4 ,it becomes
 somewhat soured2 it becomes slightly   
curdled1 and acquires a peculiarly      
pleasant taste and an aroma which was   
not present in the original fresh cream4
 ,after this ripening the cream is      
churned4 ,it is during the ripening that
 the bacteria produce their effect1 for 

after the churning they are of less     
importance4 ,part of them collect in the
 butter1 part of them are washed off    
from the butter in the buttermilk and   
the subsequent processes4 ,most of the  
bacteria that are left in the butter    
soon die1 not finding there a favourable
 condition for growth2 some of them1    
however1 live and grow for some time and
 are prominent agents in the changes by 
which butter becomes rancid4 ,the butter
 maker is concerned with the ripening   
rather than with later processes4  ,the 
object of the ripening of cream is to   
render it in a better condition for     
butter making4 ,the butter maker has    
learned by long- experience that ripened
 cream churns more rapidly than sweet   
cream1 and that he obtains a larger     
yield of butter therefrom4 ,the great   
object of the ripening1 however1 is to  
develop in the butter the peculiar      
flavour and aroma which is              
characteristic of the highest product4  
,sweet cream butter lacks flavour and   

aroma1 having indeed a taste almost     
identically the same as cream4 ,butter1 
however1 that is made from ripened cream
 has a peculiar delicate flavour and    
aroma which is well known to lovers of  
butter1 and which is developed during   
the ripening process4  ,bacteriologists 
have been able to explain with a        
considerable degree of accuracy the     
object of this ripening4 ,the process is
 really a fermentation comparable to the
 fermentation that takes place in a     
brewer's malt4 ,the growth of bacteria  
during the ripening produces chemical   
changes of a somewhat complicated       
character1 and concerns each of the     
ingredients of the milk4 ,the           
lactic-acid organisms affect the milk   
sugar and produce lactic acid2 others   
act upon the fat1 producing slight      
changes therein2 while others act upon  
the casein and the albumens of the milk4
 ,as a result1 various biproducts of    
decomposition arise1 and it is these    
biproducts of decomposition that make   

the difference between the ripened and  
the unripened cream4 ,they render it    
sour and curdle it1 and they also       
produce the flavours and aromas that    
characterize it4 ,products of           
decomposition are generally looked upon 
as undesirable for food1 and this is    
equally true of these products that     
arise in cream if the decomposition is  
allowed to continue long enough4 ,if the
 ripening1 instead of being stopped at  
the end of a day or two1 is allowed to  
continue several days1 the cream becomes
 decayed and the butter made therefrom  
is decidedly offensive4 ,but under the  
conditions of ordinary ripening1 when   
the process is stopped at the right     
moment1 the decomposition products are  
pleasant rather than unpleasant1 and the
 flavours and aromas which they impart  
to the cream and to the subsequent      
butter are those that are desired4 ,it  
is these decomposition products that    
give the peculiar character to a high   
quality of butter1 and this peculiar    

quality is a matter that determines the 
price which the butter maker can obtain 
for his product4  ,but1 unfortunately1  
the butter maker is not always able to  
depend upon the ripening4 ,while        
commonly it progresses in a satisfactory
 manner1 sometimes1 for no reason that  
he can assign1 the ripening does not    
progress normally4 ,instead of          
developing the pleasant aroma and       
flavour of the properly ripened cream1  
the cream develops unpleasant tastes4   
,it may be bitter or somewhat tainted1  
and just as sure as these flavours      
develop in the cream1 so sure does the  
quality of the butter suffer4 ,moreover1
 it has been learned by experience that 
some creameries are incapable of        
obtaining an equally good ripening of   
their cream4 ,while some of them will   
obtain favourable results1 others1 with 
equal care1 will obtain a far less      
favourable flavour and aroma in their   
butter4 ,the reason for all this has    
been explained by modern bacteriology4  

,in the milk1 and consequently in the   
cream1 there are always found many      
bacteria1 but these are not always of   
the same kinds4 ,there are scores1 and  
probably hundreds1 of species of        
bacteria common in and around our barns 
and dairies1 and the bacteria that are  
abundant and that grow in different lots
 of cream will not be always the same4  
,it makes a decided difference in the   
character of the ripening1 and in the   
consequent flavours and aromas1 whether 
one or another species of bacteria has  
been growing in the cream4 ,some species
 are found to produce good results with 
desired flavours1 while others1 under   
identical conditions1 produce decidedly 
poor results with undesired flavours4   
,if the butter maker obtains cream which
 is filled with a large number of       
bacteria capable of producing good      
flavours1 then the ripening of his cream
 will be satisfactory and his butter    
will be of high quality4 ,if1 however1  
it chances that his cream contains only 

the species which produce unpleasant    
flavours1 then the character of the     
ripening will be decidedly inferior and 
the butter will be of a poorer grade4   
,fortunately the majority of the kinds  
of bacteria liable to get into the cream
 from ordinary sources are such as      
produce either good effects upon the    
cream or do not materially influence the
 flavour or aroma4 ,hence it is that the
 ripening of cream will commonly produce
 good results4 ,bacteriologists have    
learned that there are some species of  
bacteria more or less common around our 
barns which produce undesirable effects 
upon flavour1 and should these become   
especially abundant in the cream1 then  
the character of the ripening and the   
quality of the subsequent butter will   
suffer4 ,these malign species of        
bacteria1 however1 are not very common  
in properly kept barns and dairies4     
,hence the process that is so widely    
used1 of simply allowing cream to ripen 
under the influence of any bacteria that

 happen to be in it1 ordinarily produces
 good results4 ,but our butter makers   
sometimes find1 at the times when the   
cattle change from winter to summer or  
from summer to winter feed1 that the    
ripening is abnormal4 ,the reason       
appears to be that the cream has become 
infested with an abundance of malign    
species4 ,the ripening that they produce
 is therefore an undesirable one1 and   
the quality of the butter is sure to    
suffer4  ,so long as butter was made    
only in private dairies it was a matter 
of comparatively little importance if   
there was an occasional falling off in  
quality of this sort4 ,when it was made 
a few pounds at a time1 and only once or
 twice a week1 it was not a very serious
 matter if a few churnings of butter did
 suffer in quality4 ,but to-day the     
butter-making industries are becoming   
more and more concentrated into large   
creameries1 and it is a matter of a good
 deal more importance to discover some  
means by which a uniformly high quality 

can be insured4 ,if a creamery which    
makes five hundred pounds of butter per 
day suffers from such an injurious      
ripening1 the quality of its butter will
 fall off to such an extent as to       
command a lower price1 and the creamery 
suffers materially4 ,perhaps the        
continuation of such a trouble for two  
or three weeks would make a difference  
between financial success and failure in
 the creamery4 ,with our concentration  
of the butter- making industries it is  
becoming thus desirable to discover some
 means of regulating this process more  
accurately4  ,the remedy of these       
occasional ill effects in cream ripening
 has not been within the reach of the   
butter maker4 ,the butter maker must    
make butter with the cream that is      
furnished him1 and if that cream is     
already impregnated with malign species 
of bacteria he is helpless4 ,it is true 
that much can be done to remedy these   
difficulties by the exercise of especial
 care in the barns of the patrons of the

 creamery4 ,if the barns1 the cows1 the 
dairies1 the milk vessels1 etc41 are all
 kept in condition of strict            
cleanliness1 if especial care is taken  
particularly at the seasons of the year 
when trouble is likely to arise1 and if 
some attention is paid to the kind of   
food which the cattle eat1 as a rule the
 cream will not become infected with    
injurious bacteria4 ,it may be taken as 
a demonstrated fact that these malign   
bacteria come from sources of filth1 and
 the careful avoidance of all such      
sources of filth will in a very large   
measure prevent their occurrence in the 
cream4 ,such measures as these have been
 found to be practicable in many        
creameries4 ,creameries which make the  
highest priced and the most uniform     
quality of butter are those in which the
 greatest care is taken in the barns and
 dairies to insure cleanliness and in   
the handling of the milk and cream4     
,with such attention a large portion of 
the trouble which arises in the         

creameries from malign bacteria may be  
avoided4  ,but these methods furnish no 
sure remedy against evils of improper   
species of bacteria in cream ripening1  
and do not furnish any sure means of    
obtaining uniform flavour in butter4    
,even under the very best conditions the
 flavour of the butter will vary with   
the season of the year4 ,butter made in 
the winter is inferior to that made in  
the summer months2 and while this is    
doubtless due in part to the different  
food which the cattle have and to the   
character of the cream resulting        
therefrom1 these differences in the     
flavour of the butter are also in part  
dependent upon the different species of 
bacteria which are present in the       
ripening of cream at different seasons4 
,the species of bacteria in ,june cream 
are different from those that are       
commonly present in ,january cream1 and 
this is certainly a factor in           
determining the difference between      
winter and summer butter4  ,,use ,,of   

,,artificial ,,bacteria ,,cultures ,,for
 ,,cream ,,ripening4  ,bacteriologists  
have been for some time endeavouring to 
aid butter makers in this direction by  
furnishing them with the bacteria       
needful for the best results in cream   
ripening4 ,the method of doing this is  
extremely simple in principle1 but      
proves to be somewhat difficult in      
practice4 ,it is only necessary to      
obtain the species of bacteria that     
produce the highest results1 and then to
 furnish these in pure culture and in   
large quantity to the butter makers1 to 
enable them to inoculate their cream    
with the species of bacteria which will 
produce the results that they desire4   
,for this purpose bacteriologists have  
been for several years searching for the
 proper species of bacteria to produce  
the best results1 and there have been   
put upon the market for sale several    
distinct pure cultures for this purpose4
 ,these have been obtained by different 
bacteriologists and dairymen in the     

northern ,european countries and also in
 the ,united ,states4 ,these pure       
cultures are furnished to the dairymen  
in various forms1 but they always       
consist of great quantities of certain  
kinds of bacteria which experience has  
found to be advantageous for the purpose
 of cream ripening4  ,there have        
hitherto appeared a number of           
difficulties in the way of reaching     
complete success in these directions4   
,the most prominent arises in devising a
 method of using pure cultures in the   
creamery4 ,the cream which the butter   
makers desire to ripen is1 as we have   
seen1 already impregnated with bacteria1
 and would ripen in a fashion of its own
 even if no pure culture of bacteria    
were added thereto4 ,pure cultures can  
not therefore be used as simply as can  
yeast in bread dough4 ,it is plain that 
the simple addition of a pure culture to
 a mass of cream would not produce the  
desired effects1 because the cream would
 be ripened then1 not by the pure       

culture alone1 but by the pure culture  
plus all of the bacteria that were      
originally present4 ,it would1 of       
course1 be something of a question as to
 whether under these conditions the     
results would be favourable1 and it     
would seem that this method would not   
furnish any means of getting rid of bad 
tastes and flavours which have come from
 the presence of malign species of      
bacteria4 ,it is plainly desirable to   
get rid of the cream bacteria before the
 pure culture is added4 ,this can be    
readily done by heating it to a         
temperature of #fi degrees ,c4 7#aee    
degrees ,f47 for a short time1 this     
temperature being sufficient to destroy 
most of the bacteria4 ,the subsequent   
addition of the pure culture of         
cream-ripening bacteria will cause the  
cream to ripen under the influence of   
the added culture alone4 ,this method   
proves to be successful1 and in the     
butter making countries in ,europe it is
 becoming rapidly adopted4  ,in this    

country1 however1 this process has not  
as yet become very popular1 inasmuch as 
the heating of the cream is a matter of 
considerable expense and trouble1 and   
our butter makers have not been very    
ready to adopt it4 ,for this reason1 and
 also for the purpose of familiarizing  
butter makers with the use of pure      
cultures1 it has been attempted to      
produce somewhat similar though less    
uniform results by the use of pure      
cultures in cream without previous      
healing4 ,in the use of pure cultures in
 this way1 the butter maker is directed 
to add to his cream a large amount of a 
prepared culture of certain species of  
bacteria1 upon the principle that the   
addition of such a large number of      
bacteria to the cream1 even though the  
cream is already inoculated with certain
 bacteria1 will produce a ripening of   
the cream chiefly influenced by the     
artificially added culture4 ,the culture
 thus added1 being present in very much 
greater quantity than the other wild    

species1 will have a much greater effect
 than any of them4 ,this method1 of     
course1 cannot insure uniformity4 ,while
 it may work satisfactorily in many     
cases1 it is very evident that in       
others1 when the cream is already filled
 with a large number of malign species  
of bacteria1 such an artificial culture 
would not produce the desired results4  
,this appears to be not only the        
theoretical but the actual experience4  
,the addition of such pure cultures in  
many cases produces favourable results1 
but it does not always do so1 and the   
result is not uniform4 ,while the use of
 pure cultures in this way is an        
advantage over the method of simply     
allowing the cream to ripen normally    
without such additions1 it is a method  
that is decidedly inferior to that which
 first pasteurizes the cream and        
subsequently adds a starter4  ,there is 
still another method of adding bacteria 
to cream to insure a more advantageous  
ripening1 which is frequently used1 and1

 being simpler1 is in many cases a      
decided advantage4 ,this method is by   
the use of what is called a natural     
starter4 ,a natural starter consists    
simply of a lot of cream which has been 
taken from the most favourable source   
possible--that is1 from the cleanest and
 best dairy1 or from the herd producing 
the best quality of cream--and allowing 
this cream to stand in a warm place for 
a couple of days until it becomes sour4 
,the cream will by that time be filled  
with large numbers of bacteria1 and this
 is then put as a starter into the vat  
of cream to be ripened4 ,of course1 in  
the use of this method the butter maker 
has no control over the kinds of        
bacteria that will grow in the starter1 
but it is found1 practically1 that if   
the cream is taken from a good source   
the results are extremely favourable1   
and there is produced in this way almost
 always an improvement in the butter4   
,the use of pure cultures is still quite
 new1 particularly in this country4 ,in 

the ,european butter-making countries   
they have been used for a longer period 
and have become very much better known4 
,what the future may develop along this 
line it is difficult to say2 but it     
seems at least probable that as the     
difficulties in the details are mastered
 the time will come when starters will  
be used by our butter makers for their  
cream ripening1 just as yeast is used by
 housewives for raising bread1 or by    
brewers for fermenting malt4 ,these     
starters will probably in time be       
furnished by bacteriologists4           
,bacteriology1 in other words1 is       
offering in the near future to our      
butter makers a method of controlling   
the ripening of the cream in such a way 
as to insure the obtaining of a high and
 uniform quality of butter1 so far1 at  
least1 as concerns flavour and aroma4   
,,bacteria ,,in ,,cheese4  ,cheese      
ripening4--,the third great product of  
the dairy industry is cheese1 and in    
connection with this product the        

dairyman is even more dependent upon    
bacteria than he is in the production of
 butter4 ,in the manufacture of cheese  
the casein of the milk is separated from
 the other products by the use of       
rennet1 and is collected in large masses
 and pressed1 forming the fresh cheese4 
,this cheese is then set aside for      
several weeks1 and sometimes for months1
 to undergo a process that is known as  
ripening4 ,during the ripening there are
 developed in the cheese the peculiar   
flavours which are characteristic of the
 completed product4 ,the taste of       
freshly made cheese is extremely unlike 
that of the ripened product4 ,while     
butter made from unripened cream has a  
pleasant flavour1 and one which is in   
many places particularly enjoyed1 there 
is nowhere a demand for unripened       
cheese1 for the freshly made cheese has 
a taste that scarce any one regards as  
pleasant4 ,indeed1 the whole value of   
the cheese is dependent upon the flavour
 of the product1 and this flavour is    

developed during the ripening4  ,the    
cheese maker finds in the ripening of   
his cheese the most difficult part of   
his manufacture4 ,it is indeed a process
 over which he has very little control4 
,even when all conditions seem to be    
correct1 when cheese is made in the most
 careful manner1 it not infrequently    
occurs that the ripening takes place in 
a manner that is entirely abnormal1 and 
the resulting cheese becomes worthless4 
,the cheese maker has been at an entire 
loss to understand these irregularities1
 nor has he possessed any means of      
removing them4 ,the abnormal ripening   
that occurs takes on various types4     
,sometimes the cheese will become       
extraordinarily porous1 filled with     
large holes which cause the cheese to   
swell out of proper shape and become    
worthless4 ,at other times various spots
 of red or blue appear in the           
manufactured cheese2 while again        
unpleasant tastes and flavours develop  
which render the product of no value4   

,sometimes a considerable portion of the
 product of the cheese factory undergoes
 such irregular ripening1 and the       
product for a long time will thus be    
worthless4 ,if some means could be      
discovered of removing these            
irregularities it would be a great boon 
to the cheese manufacturer2 and very    
many attempts have been made in one way 
or another to furnish the cheese maker  
with some details in the manufacture    
which will enable him in a measure to   
control the ripening4  ,the ripening of 
the cheese has been subjected to a large
 amount of study on the part of         
bacteriologists who have been interested
 in dairy products4 ,that the ripening  
of cheese is the result of bacterial    
growth therein appears to be probable   
from a priori grounds4 ,like the        
ripening of cream1 it is a process that 
occurs somewhat slowly4 ,it is a        
chemical change which is accompanied by 
the destruction of proteid matter2 it   
takes place best at certain             

temperatures1 and temperatures which we 
know are favourable to the growth of    
micro-organisms1 all of which phenomena 
suggest to us the action of bacteria4   
,moreover1 the flavours and the tastes  
that arise have a decided resemblance in
 many cases to the decomposition        
products of bacteria1 strikingly so in  
,limburger cheese4 ,when we come to     
study the matter of cheese ripening     
carefully we learn beyond question that 
this a priori conclusion is correct4    
,the ripening of any cheese is dependent
 upon several different factors4 ,the   
method of preparation1 the amount of    
water left in the curd1 the temperature 
of ripening1 and other miscellaneous    
factors connected with the mechanical   
process of cheese manufacture1 affect   
its character4 ,but1 in addition to all 
these factors1 there is undoubtedly     
another one1 and that is the number and 
the character of the bacteria that      
chance to be in the curd when the cheese
 is made4 ,while it is found that       

cheeses which are treated by different  
processes will ripen in a different     
manner1 it is also found that two       
cheeses which have been made under      
similar conditions and treated in       
identically the same way may also ripen 
in a different manner1 so that the      
resulting flavour will vary4 ,the       
variations between cheeses thus made may
 be slight or they may be considerable1 
but variations certainly do occur4      
,every one knows the great difference in
 flavours of different cheeses1 and     
these flavours are due in considerable  
measure to factors other than the simple
 mechanical process of making the       
cheese4 ,the general similarity of the  
whole process to a bacterial            
fermentation leads us to believe at the 
outset that some of the differences in  
character are due to different kinds of 
bacteria that multiply in the cheese and
 produce decomposition therein4  ,when  
the matter comes to be studied by       
bacteriology1 the demonstration of this 

position becomes easy4 ,that the        
ripening of cheese is due to growth of  
bacteria is very easily proved by       
manufacturing cheeses from milk which is
 deprived of bacteria4 ,for instance1   
cheeses have been made from milk that   
has been either sterilized or           
pasteurized--which processes destroy    
most of the bacteria therein--and1      
treated otherwise in a normal manner1   
are set aside to ripen4 ,these cheeses  
do ,,not ripen1 but remain for months   
with practically the same taste that    
they had originally4 ,in other          
experiments the cheese has been treated 
with a small amount of disinfective1    
which is sufficient to prevent bacteria 
from growing1 and again ripening is     
found to be absolutely prevented4       
,furthermore1 if the cheese under       
ordinary conditions is studied during   
the ripening process1 it is found that  
bacteria are growing during the whole   
time4 ,these facts all taken together   
plainly prove that the ripening of      

cheese is a fermentation due to         
bacteria4 ,it will be noticed1 however1 
that the conditions in the cheese are   
not favourable for very rapid bacterial 
growth4 ,it is true that there is plenty
 of food in the cheese for bacterial    
life1 but the cheese is not very moist2 
it is extremely dense1 being subjected  
in all cases to more or less pressure4  
,the penetration of oxygen into the     
centre of the mass must be extremely    
slight4 ,the density1 the lack of a     
great amount of moisture1 and the lack  
of oxygen furnish conditions in which   
bacteria will not grow very rapidly4    
,the conditions are far less favourable 
than those of ripening cream1 and the   
bacteria do not grow with anything like 
the rapidity that they grow in cream4   
,indeed1 the growth of these organisms  
during the ripening is extremely slow   
compared to the possibilities of        
bacterial growth that we have already   
noticed4 ,nevertheless1 the bacteria do 
multiply in the cheese1 and as the      

ripening goes on they become more and   
more abundant1 although the number      
fluctuates1 rising and falling under    
different conditions4  ,when the attempt
 is made to determine the relation of   
the different kinds of ripening to      
different kinds of bacteria1 it has thus
 far met with extremely little success4 
,that different flavours are due to the 
ripening produced by different kinds of 
bacteria would appear to be almost      
certain when we remember1 as we have    
already noticed1 the different kinds of 
decomposition produced by different     
species of bacteria4 ,it would seem1    
moreover1 that it ought not to be very  
difficult to separate from the ripened  
cheese the bacteria which are present1  
and thus obtain the kind of bacteria    
necessary to produce the desired        
ripening4 ,but for some reason this does
 not prove to be so easy in practice as 
it seems to be in theory4 ,many         
different species of bacteria have been 
separated from cheeses4 ,one            

bacteriologist1 studying several        
cheeses1 separated about eighty         
different species therefrom1 and others 
have found perhaps as many more from    
different sources4 ,moreover1           
experiments have been made with a       
considerable number of these different  
kinds of bacteria to determine whether  
they are capable of producing normal    
ripening4 ,these experiments consist of 
making cheese out of milk that has been 
deprived of its bacteria1 and which has 
been inoculated with large quantities of
 the species in question4 ,hitherto     
these experiments have not been very    
satisfactory4 ,in some cases the cheese 
appears to ripen scarcely at all2 in    
other cases the ripening occurs1 but the
 resulting cheese is of a peculiar      
character1 entirely unlike the cheese   
that it is desired to imitate4 ,there   
have been one or two experiments in     
recent times that give a little more    
promise of success than the earlier     
ones1 for a few species of bacteria have

 been used in ripening with what the    
authors have thought to be promising    
success4 ,the cheese made from the milk 
artificially inoculated with these      
species ripens in a satisfactory manner 
and gives some of the character desired1
 though up to the present time in no    
case has the typical normal ripening    
been produced in any of these           
experiments4  ,but these experiments    
have demonstrated beyond question that  
the abnormal ripening which is common in
 cheese factories is due to the presence
 of undesirable species of bacteria in  
the milk4 ,many of the experiments in   
making cheeses by means of artificial   
cultures of bacteria have resulted in   
decidedly abnormal cheeses4 ,many of the
 cheeses thus manufactured have shown   
imperfections in ripening which are     
identical with those actually occurring 
in the cheese factory4 ,several         
different species of bacteria have been 
found which1 when artificially used thus
 for ripening cheese1 will give rise to 

the porosity and the abnormal swelling  
of the cheese already referred to 7,fig4
 #bd74 ,others produced bad tastes and  
flavours1 and enough has been done in   
this line to demonstrate beyond         
peradventure that the abnormal ripening 
of cheese is due primarily to the growth
 of improper species therein4 ,quite a  
long list of species of bacteria which  
produce abnormal ripening have been     
isolated from cheeses1 and have been    
studied and experimented with by        
bacteriologists4 ,as a result of this   
study of abnormal ripening1 there has   
been suggested a method of partially    
controlling these--remedying them4 ,the 
method consists simply in testing the   
fermenting qualities of the milk used4  
,a small sample of milk from different  
dairies is allowed to stand in the      
cheese factory by itself until it       
undergoes its normal souring4 ,if the   
fermentation or souring that thus occurs
 is of a normal character1 the milk is  
regarded as proper for cheese making4   

,but if the fermentation that occurs in 
any particular sample of milk is        
unusual2 if an extraordinary amount of  
gas bubbles are produced1 or if         
unpleasant smells and tastes arise1 the 
sample is regarded as unfavourable for  
cheese making1 and as likely to produce 
abnormal ripening in the cheeses4 ,milk 
from this source would therefore be     
excluded from the milk that is to be    
used in cheese making4 ,this1 of course1
 is a tentative and an unsatisfactory   
method of controlling the ripening1 and 
yet it is one of some practical value to
 cheese makers4 ,it is the only method  
that has yet been suggested of          
controlling the ripening4  ,our         
bacteriologists1 of course1 are quite   
confident that in the future more       
practical results will be obtained along
 this line than in the past4 ,if it is  
true that cheeses are ripened by        
bacteria2 if it is true that different  
qualities in the cheese are due to the  
growth of different species of bacteria 

during the ripening1 it would seem to be
 possible to obtain the proper kind of  
bacteria and to furnish them to the     
cheese maker for artificially           
inoculating his cheese1 just as it has  
been possible to furnish artificially   
cultivated yeasts to the brewer1 and as 
it has become possible to furnish       
artificially cultivated bacteria to the 
butter maker4 ,we must1 however1        
recognise this to be a matter for the   
future4 ,up to the present time no      
practical results along the lines of    
bacteria have been obtained which our   
cheese manufacturers can make use of in 
the way of controlling with any accuracy
 this process of cheese ripening4  ,thus
 it will be seen that in this last dairy
 product bacteria play even a more      
important part than in any of the       
others4 ,the food value of cheese is    
dependent upon the casein which is      
present4 ,the market price1 however1 is 
controlled entirely by the flavour1 and 
this flavour is a product of bacterial  

growth4 ,upon the action of bacteria1   
then1 the cheese maker is absolutely    
dependent2 and when our bacteriologists 
are able in the future to investigate   
this matter further1 it seems to be at  
least possible that they may obtain some
 means of enabling the cheese maker to  
control the ripening accurately4 ,not   
only so1 but recognising the great      
variety in the flavours of cheese1 and  
recognising that different kinds of     
bacteria undoubtedly produce different  
kinds of decomposition products1 it     
seems to be at least possible that a    
time will come when the cheese maker    
will be able to produce at-- will any   
particularly desired flavour in his     
cheese by the addition to it of         
particular species of bacteria1 or      
particular mixtures of species of       
bacteria which have been discovered to  
produce the desired effects4            
,,chapter ,,iv4  ,,bacteria ,,in        
,,natural ,,processes4--,,agriculture4  
,thus far1 in considering the relations 

of bacteria to mankind1 we have taken   
into account only the arts and          
manufactures1 and have found bacteria   
playing no unimportant part in many of  
the industries of our modern civilized  
life4 ,so important are they that there 
is no one who is not directly affected  
by them4 ,there is hardly a moment in   
our life when we are not using some of  
the direct or indirect products of      
bacterial action4 ,we turn now1 however1
 to the consideration of a matter of    
even more fundamental importance2 for   
when we come to study bacteria in       
,nature1 we find that there are certain 
natural processes connected with the    
life of animals and plants that are     
fundamentally based upon their powers4  
,living ,nature appears limitless1 for  
life processes have been going on in the
 world through countless centuries with 
seemingly unimpaired vigour4 ,at the    
very bottom we find this never-ending   
exhibition of vital power dependent upon
 certain activities of micro-organisms4 

,so thoroughly is this true that1 as we 
shall find after a short consideration1 
the continuance of life upon the surface
 of the world would be impossible if    
bacterial action were checked for any   
considerable length of time4 ,the life  
of the globe is1 in short1 dependent    
upon these micro-organisms4  ,,bacteria 
,,as ,,scavengers4  ,in the first place1
 we may notice the value of these       
organisms simply as scavengers1 keeping 
the surface of the earth in the proper  
condition for the growth of animals and 
plants4 ,a large tree in the forest dies
 and falls to the ground4 ,for a while  
the tree trunk lies there a massive     
structure1 but in the course of months a
 slow change takes place in it4 ,the    
bark becomes softened and falls from the
 wood4 ,the wood also becomes more or   
less softened2 it is preyed upon then by
 insect life2 its density decreases more
 and more1 until finally it crumbles    
into a soft1 brownish1 powdery mass1 and
 eventually the whole sinks into the    

soil1 is overgrown by mosses and other  
vegetation1 and the tree trunk has      
disappeared from view4 ,in the same way 
the body of the dead animal undergoes   
the process of the softening of its     
tissues by decay4 ,the softer parts of  
the body rapidly dissipate1 and even the
 bones themselves eventually are covered
 with the soil and disintegrated1 until 
in time they1 too1 disappear from any   
visible existence4 ,this whole process  
is one of decay1 and the result is that 
the solid mass of the body of the tree  
or of the animal has been decomposed4   
,what has become of it8 ,the answer     
holds the secret of ,nature's eternal   
freshness4 ,part of it has dissipated   
into the air in the form of gases and   
water vapour2 part of it has changed its
 composition and has become incorporated
 into the soil1 the final result being  
that the body of the plant or animal    
disappears as such1 and its substance is
 converted into gaseous form1 which is  
dissipated in the air or into simple    

compounds which sink into the earth4    
,this whole process of decay of organic 
life is one in which bacteria play the  
most important part4 ,in the case of the
 decomposition of the woody matter of   
the tree trunk1 the process is begun by 
the agency of moulds1 for this group of 
organisms alone appears to be capable of
 attacking such hard woody structure4   
,the later part of the decay1 however1  
is largely carried on by bacterial life4
 ,in the decomposition of the animal    
tissues1 bacteria alone are the agents4 
,thus the process by which organic      
matter is dissipated into the air or    
incorporated into the soil is one which 
is primarily presided over by bacterial 
life4  ,viewing this matter in a purely 
mechanical light1 the importance of     
bacteria in thus acting as scavengers   
can hardly be overestimated4 ,if we     
think for a moment of the condition of  
the world were there no such decomposing
 agents to rid the earth's surface of   
the dead bodies of animals and plants1  

we shall see that long since the earth  
would have been uninhabitable4 ,if the  
dead bodies of plants and animals of    
past ages simply accumulated on the     
surface of the ground without any forces
 to reduce them into simple compounds   
for dissipation1 by their very bulk they
 would have long since completely       
covered the surface of the earth so as  
to afford no possible room for further  
growth of plants and animals4 ,in a     
purely mechanical way1 then1 bacteria as
 decomposition agents are necessary to  
keep the surface of the earth fresh and 
unencumbered so that life can continue4 
,,bacteria ,,as ,,agents ,,in           
,,nature',s ,,food ,,cycle4  ,but the   
matter by no means ends here4 ,when we  
come to think of it1 it is a matter of  
considerable surprise that the surface  
of the earth has been able to continue  
producing animals and plants for the    
many millions of years during which life
 has been in existence4 ,plants and     
animals both require food1 animals      

depending wholly upon plants therefor4  
,plants1 however1 equally with animals1 
require food1 and although they obtain a
 considerable portion of their food from
 the air1 yet no inconsiderable part of 
it is obtained from the soil4 ,the      
question is forced upon us1 therefore1  
as to why the soil has not long since   
become exhausted of food4 ,how could the
 soil continue to support plants year   
after year for millions of years1 and   
yet remain as fertile as ever8  ,the    
explanation of this phenomenon is in the
 simple fact that the processes of      
,nature are such that the same food is  
used over and over again1 first by the  
plant1 then by the animal1 and then     
again by the plant1 and there is no     
necessity for any end of the process so 
long as the sun furnishes energy to keep
 the circulation continuous4 ,one phase 
of this transference of food from animal
 to plant and from plant to animal is   
familiar to nearly every one4 ,it is a  
well-known fact that animals in their   

respiration consume oxygen1 but exhale  
it again in combination with carbon as  
carbonic dioxide4 ,on the other hand1   
plants in their life consume the        
carbonic dioxide and exhale the oxygen  
again as free oxygen4 ,thus each of     
these kingdoms makes use of the excreted
 product of the other1 and this process 
can go on indefinitely1 the animals     
furnishing our atmosphere with plenty of
 carbonic acid for plant life1 and the  
plants excreting into the atmosphere at 
the same time an abundant sufficiency of
 oxygen for animal life4 ,the oxygen    
thus passes in an endless round from    
animal to plant and from plant to       
animal4  ,a similar cycle is true of all
 the other foods of animal and plant    
life1 though in regard to the others the
 operation is more complex and more     
members are required to complete the    
chain4 ,the transference of matter      
through a series of changes by which it 
is brought from a condition in which it 
is proper food for plants back again    

into a condition when it is once more a 
proper food for plants1 is one of the   
interesting discoveries of modern       
science1 and one in which1 as we shall  
see1 bacteria play a most important     
part4 ,this food cycle is illustrated   
roughly by the accompanying diagram2 but
 in order to understand it1 an          
explanation of the various steps in this
 cycle is necessary4  ,it will be       
noticed that at the bottom of the circle
 represented in ,fig4 #be1 at ,a1 are   
given various ingredients which are     
found in the soil and which form plant  
foods4 ,plant foods1 as may be seen     
there1 are obtained partly from the air 
as carbonic dioxide and water2 but      
another portion comes from the soil4    
,among the soil ingredients the most    
prominent are nitrates1 which are the   
forms of nitrogen compounds most easily 
made use of by plants as a source of    
this important element4 ,it should be   
stated also that there are other        
compounds in the soil which furnish     

plants with part of their               
food--compounds containing potassium1   
phosphorus1 and some other elements4    
,for simplicity's sake1 however1 these  
will be left out of consideration4      
,beginning at the bottom of the cycle   
7,fig4 #be ,a71 plant life seizes the   
gases from the air and these foods from 
the soil1 and by means of the energy    
furnished it by the sun's rays builds   
these simple chemical compounds into    
more complex ones4 ,this gives us the   
second step1 as shown in ,fig4 #be ,b1  
the products of plant life4 ,these      
products of plant life consist of such  
materials as sugar1 starches1 fats1 and 
proteids1 all of which have been        
manufactured by the plant from the      
ingredients furnished it from the soil  
and air1 and through the agency of the  
sun's rays4 ,these products of plant    
life now form foods for the animal      
kingdom4 ,starches1 fats1 and proteids  
are animal foods1 and upon such complex 
bodies alone can the animal kingdom be  

fed4 ,animal life1 standing high up in  
the circle1 is not capable of extracting
 its nutriment from the soil1 but must  
take the more complex foods which have  
been manufactured by plant life4 ,these 
complex foods enter now into the animal 
and take their place in the animal body4
 ,by the animal activities1 some of the 
foods are at once decomposed into       
carbonic acid and water1 which1 being   
dissipated into the air1 are brought    
back at once into the condition in which
 they can serve again as plant food4    
,this part of the food is thus brought  
back again to the bottom of the circle  
7,fig4 #be1 dotted lines74 ,but while it
 is true that animals do thus reduce    
some of their foods to the simple       
condition of carbonic acid and water1   
this is not true of most of the foods   
which contain nitrogen4 ,the nitrogenous
 foods are as necessary for the life as 
the carbon foods1 and animals do not    
reduce their nitrogenous foods to the   
condition in which plants can prey upon 

them4 ,while plants furnish them with   
nitrogenous food1 they can not give it  
back to the plants4 ,part of the        
nitrogenous foods animals build into new
 albumins 7,fig4 #be ,c72 but a part of 
them they reduce at once into a somewhat
 simpler condition known as urea4 ,urea 
is the form in which the nitrogen is    
commonly excreted from the animal body4 
,but urea is not a plant food2 for      
ordinary plants are entirely unable to  
make use of it4 ,part of the nitrogen   
eaten by the animal is stored up in its 
body1 and thus the body of the animal1  
after it has died1 contains these       
nitrogen compounds of high complexity4  
,but plants are not able to use these   
compounds4 ,a plant can not be fed upon 
muscle tissue1 nor upon fats1 nor bones1
 for these are compounds so complex that
 the simple plant is unable to use them 
at all4 ,so far1 then1 in the food cycle
 the compounds taken from the soil have 
been built up into compounds of greater 
and greater complexity2 they have       

reached the top of this circle1 and no  
part of them1 except part of the carbon 
and oxygen1 has become reduced again to 
plant food4 ,in order that this material
 should again become capable of entering
 into the life of plants so as to go    
over the circle again1 it is necessary  
for it to be once more reduced from its 
highly complex condition into a simpler 
one4  ,now come into play these         
decomposition agencies which we have    
been studying under the head of         
scavengers4 ,it will be noticed that the
 next step in the food cycle is taken by
 the decomposition bacteria4 ,these     
organisms1 existing1 as we have already 
seen1 in the air1 in the soil1 in the   
water1 and always ready to seize hold of
 any organic substance that may furnish 
them with food1 feed upon the products  
of animal life1 whether they are such   
products as muscle tissue1 or fat1 or   
sugar1 or whether they are the excreted 
products of animal life1 such as urea1  
and produce therein the chemical        

decomposition changes already noticed4  
,as a result of this chemical           
decomposition1 the complex bodies are   
broken into simpler and simpler         
compounds1 and the final result is a    
very thorough destruction of the animal 
body or the material excreted by animal 
life1 and its reduction into forms      
simple enough for plants to use again as
 foods4 ,thus the bacteria come in as a 
necessary link to connect the animal    
body1 or the excretion from the animal  
body1 with the soil again1 and therefore
 with that part of the circle in which  
the material can once more serve as     
plant food4  ,but in the decomposition  
that thus occurs through the agency of  
the putrefactive bacteria it very       
commonly happens that some of the food  
material is broken down into compounds  
too simple for use as plant food4 ,as   
will be seen by a glance at the diagram 
7,fig4 #be ,d71 a portion of the        
cleavage products resulting from the    
destruction of these animal foods takes 

the form of carbonic-acid gas and water4
 ,these ingredients are at once in      
condition for plant life1 as shown by   
the dotted lines4 ,they pass off into   
the air1 and the green leaves of        
vegetation everywhere again seize them1 
assimilate them1 and use them as food4  
,thus it is that the carbon and the     
oxygen have completed the cycle1 and    
have come back again to the position in 
the circle where they started4 ,in      
regard to the nitrogen portion of the   
food1 however1 it very commonly happens 
that the products which arise as the    
result of the decomposition processes   
are not yet in proper condition for     
plant food4 ,they are reduced into a    
condition actually too simple for the   
use of plants4 ,as a result of these    
putrefactive changes1 the nitrogen      
products of animal life are broken      
frequently into compounds as simple as  
ammonia 7,,nh#c71 or into compounds     
which the chemists speak of as nitrites 
7,fig4 #be at ,d74 ,now these compounds 

are not ordinarily within the reach of  
plant life4 ,the luxuriant vegetation of
 the globe extracts its nitrogen from   
the soil in a form more complex than    
either of the compounds here mentioned2 
for1 as we have seen1 it is nitrates    
chiefly that furnish plants with their  
nitrogen food factor4 ,but nitrates     
contain considerable oxygen4 ,ammonia1  
which is one of the products of         
putrefactive de- composition1 contains  
no oxygen1 and nitrites1 another factor1
 contains less oxygen than nitrates4    
,these bodies are thus too simple for   
plants to make use of as a source of    
nitrogen4 ,the chemical destruction of  
the food material which results from the
 action of the putrefactive bacteria is 
too thorough1 and the nitrogen foods are
 not yet in condition to be used by     
plants4  ,now comes in the agency of    
still another class of micro-organisms1 
the existence of which has been         
demonstrated to us during the last few  
years4 ,in the soil everywhere1         

especially in fertile soil1 is a class  
of bacteria which has received the name 
of nitrifying bacteria 7,fig4 #bf74     
,these organisms grow in the soil and   
feed upon the soil ingredients4 ,in the 
course of their life they have somewhat 
the same action upon the simple nitrogen
 cleavage products just mentioned as we 
have already noticed the vinegar-       
producing species have upon alcohol1    
viz41 the bringing about a union with   
oxygen4 ,there are apparently several   
different kinds of nitrifying bacteria  
with different powers4 ,some of them    
cause an oxidation of the nitrogen      
products by means of which the ammonia  
is united with oxygen and built up into 
a series of products finally resulting  
in nitrates 7,fig4 #bf74 ,by the action 
of other species still higher nitrogen  
compounds1 including the nitrites1 are  
further oxidized and built up into the  
form of nitrates4 ,thus these nitrifying
 organisms form the last link in the    
chain that binds the animal kingdom to  

the vegetable kingdom 7,fig4 #be at #d74
 ,for after the nitrifying organisms    
have oxidized nitrogen cleavage         
products1 the results of the oxidation  
in the form of nitrates or nitric acid  
are left in the soil1 and may now be    
seized upon by the roots of plants1 and 
begin once more their journey around the
 food cycle4 ,in this way it will be    
seen that while plants1 by building up  
compounds1 form the connecting link     
between the soil and animal life1       
bacteria in the other half of the cycle1
 by reducing them again1 give us the    
connecting link between animal life and 
the soil4 ,the food cycle would be as   
incomplete without the agency of        
bacterial life as it would be without   
the agency of plant life4  ,but even yet
 the food cycle is not complete4 ,some  
of the processes of decomposition appear
 to cause a portion of the nitrogen to  
fly out of the circle at a tangent4 ,in 
the process of decomposition which is   
going on through the agency of          

micro-organisms1 a considerable part of 
the nitrogen is dissipated into the air 
in the form of free nitrogen4 ,when a   
bit of meat decays1 part of the meat is1
 indeed1 converted into ammonia or other
 nitrogen compounds1 but if the         
putrefaction is allowed to go on1 in the
 end a considerable portion of it will  
be broken into still simpler forms1 and 
the nitrogen will finally be dissipated 
into the air in the form of free        
nitrogen4 ,this dissipation of free     
nitrogen into the air is going on in the
 world wherever putrefaction takes      
place4 ,wherever decomposition of       
nitrogen products occurs some free      
nitrogen is eliminated4 ,now1 this part 
of the nitrogen has passed beyond the   
reach of plants1 for plants can not     
extract free nitrogen from the air4 ,in 
the diagram this is represented as a    
portion of the material which1 through  
the agency of the decomposition         
bacteria1 has been thrown out of the    
cycle at a tangent 7,fig4 #be ,e74 ,it  

will1 of course1 be plain from this that
 the store of nitrogen food must be     
constantly diminishing4 ,the soil may   
have been originally supplied with a    
given quantity of nitrogen compound1 but
 if the decomposition products are      
causing considerable quantities of this 
nitrogen to be dissipated in the air1 it
 plainly follows that the total amount  
of nitrogen food upon which the animal  
and vegetable kingdoms can depend is    
becoming constantly reduced by such     
dissipation4  ,there are still other    
methods by which nitrogen is being lost 
from the food cycle4 ,first1 we may     
notice that the ordinary processes of   
vegetation result in a gradual draining 
of the soil and a throwing of its       
nitrogen into the ocean4 ,the body of   
any animal or any plant that chances to 
fall into a brook or river is eventually
 carried to the sea1 and the products of
 its decomposition pass into the ocean  
and are1 of course1 lost to the soil4   
,now1 while this gradual extraction of  

nitrogen from the soil by drainage is a 
slow one1 it is nevertheless a sure one4
 ,it is far more rapid in these years of
 civilized life than in former times1   
since the products of the soil are given
 to the city1 and then are thrown into  
its sewage ,our cities1 then1 with our  
present system of disposing of sewage1  
are draining from the soil the nitrogen 
compounds and throwing them away4  ,in  
yet another direction must it be noticed
 that our nitrogen compounds are being  
lost to plant life--viz41 by the use of 
various nitrogen compounds to form      
explosives4 ,gunpowder1 nitro-glycerine1
 dynamite1 in fact1 nearly all the      
explosives that are used the world over 
for all sorts of purposes1 are nitrogen 
compounds4 ,when they are exploded the  
nitrogen of the compound is dissipated  
into the air in the form of gas1 much of
 it in the form of free nitrogen4 ,the  
basis from which explosive compounds are
 made contains nitrogen in the form in  
which it can be used by plants4         

,saltpetre1 for example1 is equally good
 as a fertilizer and as a basis for     
gunpowder4 ,the products of the         
explosion are gases no longer capable of
 use by plants1 and thus every explosion
 of nitrogen compounds aids in this     
gradual dissipation of nitrogen         
products1 taking them from the store of 
plant foods and throwing them away4     
,all of these agencies contribute to    
reduce the amount of material           
circulating in the food cycle of        
,nature1 and thus seem to tend          
inevitably in the end toward a          
termination of the processes of life2   
for as soon as the soil becomes         
exhausted of its nitrogen compounds1 so 
soon will plant life cease from lack of 
nutrition1 and the disappearance of     
animal life will follow rapidly4 ,it is 
this loss of nitrogen in large measure  
that is forcing our agriculturists to   
purchase fertilizers4 ,the last fifteen 
years have shown us1 however1 that here 
again we may look upon our friends1 the 

bacteria1 as agents for counteracting   
this dissipating tendency in the general
 processes of ,nature4 ,bacterial life  
in at least two different ways appears  
to have the function of reclaiming from 
the atmosphere more or less of this     
dissipated free nitrogen4  ,in the first
 place1 it has been found in the last   
few years that soil entirely free from  
all common plants1 but containing       
certain kinds of bacteria1 if allowed to
 stand in contact with the air1 will    
slowly but surely gain in the amount of 
nitrogen compounds that it contains4    
,these nitrogen compounds are plainly   
manufactured by the bacteria in the     
soil2 for unless the bacteria are       
present they do not accumulate1 and they
 do accumulate inevitably if the        
bacteria are present in the proper      
quantity and the proper species4 ,it    
appears that1 as a rule1 this fixation  
of nitrogen is not performed by any one 
species of microorganisms1 but by two or
 three of them acting together4 ,certain

 combinations of bacteria have been     
found which1 when inoculated in the     
soil1 will bring about this fixation of 
nitrogen1 but no one of the species is  
capable of producing this result alone4 
,we do not know to what extent these    
organisms are distributed in the soil1  
nor how widely this nitrogen fixation   
through bacterial life is going on4 ,it 
is only within a short time that it has 
been demonstrated to exist1 but we must 
look upon bacteria in the soil as one of
 the factors in reclaiming from the     
atmosphere the dissipated free nitrogen4
  ,the second method by which bacteria  
aid in the reclaiming of this lost      
nitrogen is by a combined action of     
certain species of bacteria and some of 
the higher plants4 ,ordinary green      
plants1 as already noted1 are unable to 
make use of the free nitrogen of the    
atmosphere ,it was found1 however1 some 
fifteen years ago that some species of  
plants1 chiefly the great family of     
legumes1 which contains the pea plant1  

the bean1 the clover1 etc1 are able1    
when growing in soil that is poor in    
nitrogen1 to obtain nitrogen from some  
source other than the soil in which they
 grow4 ,a pea plant in soil that        
contains no nitrogen products and       
watered with water that contains no     
nitrogen1 will1 after sprouting and     
growing for a length of time1 be found  
to have accumulated a considerable      
quantity of fixed nitrogen in its       
tissues ,the only source of this        
nitrogen has been evidently from the air
 which bathes the leaves of the plant or
 permeates the soil and bathes its roots
 ,this fact was at first disputed1 but  
subsequently demonstrated to be true1   
and was found later to be associated    
with the combined action of these       
legumes and certain soil bacteria4 ,when
 a legume thus gains nitrogen from the  
air1 it develops upon its roots little  
bunches known as root nodules or root   
tubercles4 ,the nodules are sometimes   
the size of the head of a pm1 and       

sometimes much larger than this1        
occasionally reaching the size of a     
large pea1 or even larger4 ,upon        
microscopic examination they are found  
to be little nests of bacteria ,in some 
way the soil organisms 7,fig #bg7 make  
their way into the roots of the         
sprouting plant1 and finding there      
congenial environment1 develop in       
considerable quantities and produce root
 tubercles in the root4 ,now1 by some   
entirely unknown process1 the legume and
 the bacteria growing together succeed  
in extracting the nitrogen from the     
atmosphere which permeates the soil1 and
 fixing this nitrogen in the tubercles  
and the roots in the form of nitrogen   
compounds4 ,the result is that1 after a 
proper period of growth1 the amount of  
fixed nitrogen in the plant is found to 
have very decidedly increased 7,fig #be 
,e74  ,this1 of course1 furnishes a     
starting point for the reclaiming of the
 lost atmospheric nitrogen4 ,the legume 
continues to live its usual life1       

perhaps increasing the store of nitrogen
 in its roots and stems and leaves      
during the whole of its normal growth4  
,subsequently1 after having finished its
 ordinary life1 the plant will die1 and 
then the roots and stems and leaves1    
falling upon the ground and becoming    
buried1 will be seized upon by the      
decomposition bacteria already          
mentioned4 ,the nitrogen which has thus 
become fixed in their tissues will      
undergo the destructive changes already 
described4 ,this will result eventually 
in the production of nitrates4 ,thus    
some of the lost nitrogen is restored   
again to the soil in the form of        
nitrates1 and may now start on its route
 once more around the cycle of food4    
,it will be seen1 then1 that the food   
cycle is a complete one4 ,beginning with
 the mineral ingredients in the soil1   
the food matter may start on its        
circulation from the soil to the plant1 
from the plant to the animal1 from the  
animal to the bacterium and from the    

bacterium through a series of other     
bacteria back again to the soil in the  
condition in which it started4 ,if1     
perchance1 in this progress around the  
circle some of the nitrogen is thrown   
off at a tangent1 this1 too1 is brought 
back again to the circle through the    
agency of bacterial life4 ,and so the   
food material of animals and plants     
continues in this never-ceasing         
circulation4 ,it is the sunlight that   
furnishes the energy for the motion4 ,it
 is the sunlight that forces the food   
around the circle and keeps up the      
endless change2 and so long as1 the sun 
continues to shine upon the earth there 
seems to be no reason why the process   
should ever cease4 ,it is this repeated 
circulation that has made the           
continuation of life possible for the   
millions and millions of years of the   
earth's history4 ,it is this continued  
circulation that makes life possible    
still1 and it is only this fact that the
 food is thus capable of ever           

circulating from animal to plant and    
from plant to animal that makes it      
possible for the living world to        
continue its existence4 ,but1 ah we have
 seen1 one half of this great circle of 
food change is dependent upon bacterial 
life4 ,without the bacterial life the   
animal body and the animal excretion    
could never be brought back again within
 the reach of the plant2 and thus1 were 
it not for the action of these micro-   
organisms the food cycle would be       
incomplete and life could not continue  
indefinitely upon the surface of the    
earth4 ,at the very foundation1 the     
continuation of the present condition of
 ,nature and the existence of life      
during the past history of the world has
 been fundamentally based upon the      
ubiquitous presence of bacteria and upon
 their continual action in connection   
with both destructive and constructive  
processes4  ,,relation ,,of ,,bacteria  
,,to ,,agriculture4  ,we have already   
noticed that bacteria play an important 

part in some of the agricultural        
industries1 particularly in the dairy4  
,from the consideration of the matters  
just discussed1 it is manifest that     
these organisms must have an even more  
intimate relation to the farmer's       
occupation4 ,at the foundation1 farming 
consists in the cultivation of plants   
and animals1 and we have already seen   
how essential are the bacteria in the   
continuance of animal and plant life4   
,but aside from these theoretical       
considerations1 a little study shows    
that in a very practical manner the     
farmer is ever making use of bacteria1  
as a rule1 quite unconsciously1 but none
 the less positively4  ,,sprouting ,,of 
,,seeds4  ,even in the sprouting of     
seeds after they are sown in the soil   
bacterial life has its influence4 ,when 
seeds are placed m moist soil they      
germinate under the influence of heat4  
,the rich albuminous material in the    
seeds furnishes excellent food1 and     
inasmuch as bacteria abound in the soil1

 it is inevitable that they should grow 
in and feed upon the seed4 ,if the      
moisture is excessive and the heat      
considerable1 they very frequently grow 
so rapidly in the seed as to destroy its
 life as a seedling4 ,the seed rots in  
the ground as a result4 ,this does not  
commonly occur1 however1 in ordinary    
soil4 ,but even here bacteria do grow in
 the seed1 though not so abundantly as  
to produce any injury4 ,indeed1 it has  
been claimed that their presence in the 
seed in small quantities is a necessity 
for the proper sprouting of the seed4   
,it has been claimed that their growth  
tends to soften the food material in the
 seed1 so that the young seedling can   
more readily absorb it for its own food1
 and that without such a softening the  
seed remains too hard for the plant to  
use4 ,this may well be doubted1 however1
 for seeds can apparently sprout well   
enough without the aid of bacteria4     
,but1 nevertheless1 bacteria do grow in 
the seed during its germination1 and    

thus do aid the plant in the softening  
of the food material4 ,we can not regard
 them as essential to seed germination4 
,it may well be claimed that they       
ordinarily play at least an incidental  
part in this fundamental life process1  
although it is uncertain whether the    
growth of seedlings is to any           
considerable extent aided thereby4      
,,the ,,silo4  ,in the management of a  
silo the farmer has undoubtedly another 
great bacteriological problem4 ,in the  
attempt to preserve his summer-grown    
food for the winter use of his animals1 
he is hindered by the activity of common
 bacteria4 ,if the food is kept moist1  
it is sure to undergo decomposition and 
be ruined in a short time as animal     
food4 ,the farmer finds it necessary1   
therefore1 to dry some kinds of foods1  
like hay4 ,while he can thus preserve   
some foods1 others can not be so        
treated4 ,much of the rank growth of the
 farm1 like cornstalks1 is good food    
while it is fresh1 but is of little     

value when dried4 ,the farmer has from  
experience and observation discovered a 
method of managing bacterial growth     
which enables him to avoid their        
ordinary evil effects4 ,this is by the  
use of the silo4 ,the silo is a large1  
heavily built box1 which is open only at
 the top4 ,in the silo the green food is
 packed tightly1 and when full all      
access of air is excluded1 except at its
 surface4 ,under these conditions the   
food remains moist1 but nevertheless    
does not undergo its ordinary           
fermentations and putrefactions1 and may
 be preserved for months without being  
ruined4 ,the food in such a silo may be 
taken out months after it is packed1 and
 will still be found to be in good      
condition for food4 ,it is true that it 
has changed its character somewhat1 but 
it is not decayed1 and is eagerly eaten 
by cattle4  ,we are yet very ignorant of
 the nature of the changes which occur m
 the food while in the silo4 ,the food  
is not preserved from fermentation4     

,when the siloxis packed slowly1 a very 
decided fermentation occurs by which the
 mass is raised to a high temperature   
7#adj degrees ,f4 to #afj degrees ,f474 
,this heating is produced by certain    
species of bacteria which grow readily  
even at this high temperature4 ,the     
fermentation uses up the air in the silo
 to a certain extent and produces a     
settling of the material which still    
further excludes air4 ,the first        
fermentation soon ceases1 and afterward 
only slow changes occur4 ,certain acid- 
producing bacteria after a little begin 
to grow slowly1 and in time the silage  
is rendered somewhat sour by the        
production of acetic acid4 ,but the     
exclusion of air1 the close packing1 and
 the small amount of moisture appear to 
prevent the growth of the common        
putrefactive bacteria1 and the silage   
remains good for a long time4 ,in other 
methods of filling the silo1 the food is
 very quickly packed and densely crowded
 together so as to exclude as much air  

as possible from the beginning4 ,under  
these conditions the lack of moisture   
and air prevents fermentative action    
very largely4 ,only certain             
acid-producing organisms grow1 and these
 very slowly4 ,the essential result in  
either case is that the common          
putrefactive bacteria are prevented from
 growing1 probably by lack of sufficient
 oxygen and moisture1 and thus the decay
 is prevented4 ,the closely packed food 
offers just the same unfavourable       
condition for the growth of common      
putrefactive bacteria that we have      
already seen offered by the hard-pressed
 cheese1 and the bacteria growth is in  
the same way held in check4 ,our        
knowledge of the matter is as yet very  
slight1 but we do know enough to        
understand that the successful          
management of a silo is dependent upon  
the manipulation of bacteria4  ,,the    
,,fertility ,,of ,,the ,,soil4  ,the    
farmer's sole duty is to extract food   
from the soil4 ,this he does either     

directly by raising crops1 or indirectly
 by raising animals which feed upon the 
products of the soil4 ,in either case   
the fertility of the soil is the        
fundamental factor in his success4 ,this
 fertility is a gift to him from the    
bacteria4  ,even in the first formation 
of soil he is in a measure dependent    
upon bacteria4 ,soil1 as is well known1 
is produced in large part by the        
crumbling of the rocks into powder4     
,this crumbling we generally call       
weathering1 and regard it as due to the 
effect of moisture and cold upon the    
rocks1 together with the oxidizing      
action of the air4 ,doubtless this is   
true1 and the weathering action is      
largely a physical and chemical one4    
,nevertheless1 in this fundamental      
process of rock disintegration bacterial
 action plays a part1 though perhaps a  
small one4 ,some species of bacteria1 as
 we have seen1 can live upon very simple
 foods1 finding in free nitrogen and    
carbonates sufficiently highly complex  

material for their life4 ,these         
organisms appear to grow on the bare    
surface of rocks1 assimilating nitrogen 
from the air1 and carbon from some      
widely diffused carbonates or from the  
,,co#b in the air4 ,their secreted      
products of an acid nature help to      
soften the rocks1 and thus aid in       
performing the first step in weathering4
  ,the soil is not1 however1 all made up
 of disintegrated rocks4 ,it contains1  
besides1 various ingredients which      
combine to make it fertile4 ,among these
 are various sulphates which form       
important parts of plant foods4 ,these  
sulphates appear to be formed1 in part1 
at least1 by bacterial agency4 ,the     
decomposition of proteids gives rise1   
among other things1 to hydrogen sulphide
 7,h#b,s74 ,this gas1 which is of common
 occurrence in the atmosphere1 is       
oxidized by bacterial growth into       
sulphuric acid1 and this is the basis of
 part of the soil sulphates4 ,the       
deposition of iron phosphates and iron  

silicates is probably also in a measure 
aided by bacterial action4 ,all of these
 processes are factors in the formation 
of soil4 ,beyond much question the rock 
disintegration which occurs everywhere  
in ,nature is chiefly the result of     
physical and chemical changes1 but there
 is reason for believing that the       
physical and chemical processes are1 to 
a slight extent at least1 assisted by   
bacterial life4  ,a more important      
factor of soil fertility is its nitrogen
 content1 without which it is completely
 barren4 ,the origin of these nitrogen  
ingredients has been more or less of a  
puzzle4 ,fertile soil everywhere        
contains nitrates and other nitrogen    
compounds1 and in certain parts of the  
world there are large accumulations of  
these compounds1 like the nitrate beds  
of ,chili4 ,that they have come         
ultimately from the free atmospheric    
nitrogen seems certain1 and various     
attempts have been made to explain a    
method of this nitrogen fixation4 ,it   

has been suggested that electrical      
discharges in the air may form nitric   
acid1 which would readily then unite    
with soil ingredients to form nitrates4 
,there is little reason1 however1 for   
believing this to be a very important   
factor ,but in the soil bacteria we find
 undoubtedly an efficient agency m this 
nitrogen fixation4 ,as already seen1 the
 bacteria are able to seize the free    
atmospheric nitrogen1 converting it into
 nitrite and nitrates4 ,we have also    
learned that they can act in connection 
with legumes and some other plants1     
enabling them to fix atmospheric        
nitrogen and store it m their roots4 ,by
 these two means the nitrogen ingredient
 in the soil is prevented from becoming 
exhausted by the processes of           
dissipation constantly going on4        
,further1 by some such agency must we   
imagine the original nitrogen soil      
ingredient to have been derived4 ,such  
an organic agency is the only one yet   
discerned which appears to have been    

efficient in furnishing virgin soil with
 its nitrates1 and we must therefore    
look upon bacteria as essential to the  
original fertility of the soil4 ,but in 
another direction still does the farmer 
depend directly upon bacteria ,the most 
important factor in the fertility of the
 soil is the part of it called humus4   
,this humus is very complex1 and never  
alike in different soils ,it contains   
nitrogen compounds in abundance1        
together with sulphates1 phosphates1    
sugar1 and many other substances4 ,it is
 this which makes the garden soil       
different from sand1 or the rich soil   
different from the sterile soil4 ,if the
 soil is cultivated year after year1 its
 food ingredients are slowly but surely 
exhausted4 ,something is taken from the 
humus each year1 and unless this be     
replaced the soil ceases to be able to  
support life4 ,to keep up a constant    
yield from the soil the farmer          
understands that he must apply          
fertilizers more or less constantly4    

,this application of fertilizers is     
simply feeding the crops4 ,some of these
 fertilizers the farmer purchases1 and  
knows little or nothing as to their     
origin4 ,the most common method of      
feeding the crops is1 however1 by the   
use of ordinary barnyard manure4 ,the   
reason why this material contains plant 
food we can understand1 since it is made
 of the undigested part of food1        
together with all the urea and other    
excretions of animals1 and contains1    
therefore1 besides various minerals1 all
 of the nitrogenous waste of animal     
life4 ,these secretions are not at first
 fit for plant food4 ,the farmer has    
learned by experience that such         
excretions1 before they are of any use  
on his fields1 must undergo a process of
 slow change1 which is sometimes called 
ripening4 ,fresh manure is sometimes    
used on the fields1 but it is only made 
use of by the plants after the ripening 
process has occurred4 ,fresh animal     
excretions are of little or no value as 

a fertilizer4 ,the farmer1 therefore1   
commonly allows it to remain in heaps   
for some time1 and it undergoes a slow  
change1 which gradually converts it into
 a condition in which it can be used by 
plants4 ,this ripening is readily       
explained by the facts already          
considered ,the fresh animal secretions 
consist of various highly complex       
compounds of nitrogen1 and the ripening 
is a process of their decomposition4    
,the proteids are broken to pieces1 and 
their nitrogen elements reduced to the  
form of nitrates1 leucin1 etc1 or even  
to ammonia or free nitrogen4 ,further1 a
 second process occurs1 the process of  
oxidation of these nitrogen compounds   
already noticed1 and the ammonia and    
nitrites resulting from the             
decomposition are built into nitrates4  
,in short1 in this ripening manure the  
processes noticed in the first part of  
this chapter are taking place1 by which 
the complex nitrogenous bodies are first
 reduced and then oxidized to form plant

 food4 ,the ripening of manure is both  
an analytical and a synthetical process4
 ,by the analysis1 proteids and other   
bodies are broken into very simple      
compounds1 some of them1 indeed1 being  
dissipated into the air1 but other      
portions are retained and then oxidized1
 and these latter become the real       
fertilizing materials4 ,through the     
agency of bacteria the compost heap thus
 becomes the great source of plant food 
to the farmer4 ,into this compost heap  
he throws garbage1 straw1 vegetable and 
animal substances in general1 or any    
organic refuse which may be at hand4    
,the various bacteria seize it all1 and 
cause the decomposition which converts  
it into plant food again4 ,the rotting  
of the compost heap is thus a gigantic  
cultivation of bacteria4  ,this         
knowledge of the ripening process is    
further teaching the farmer how to      
prevent waste4 ,in the ordinary         
decomposition of the compost heap not an
 inconsiderable portion of the nitrogen 

is lost in the air by dissipation as    
ammonia or free nitrogen4 ,even his     
nitrates may be thus lost by bacterial  
action4 ,this portion is lost to the    
farmer completely1 and he can only hope 
to replace it either by purchasing      
nitrates in the form of commercial      
fertilizers1 or by reclaiming it from   
the air by the use of the bacterial     
agencies already noticed4 ,with the     
knowledge now at his command he is      
learning to prevent this waste4 ,in the 
decomposition one large factor of loss  
is the ammonia1 which1 being a gas1 is  
readily dissipated into the air4        
,knowing this common result of bacterial
 action1 the scientist has told the     
farmer that1 by adding certain common   
chemicals to his decomposing manure     
heap1 chemicals which will readily unite
 with ammonia1 he may retain most of the
 nitrogen in this heap in the form of   
ammonia salts1 which1 once formed1 no   
longer show a tendency to dissipate into
 the air4 ,ordinary gypsum1 or          

superphosphates1 or plaster will readily
 unite with ammonia1 and these added to 
the manure heap largely counteract the  
tendency of the nitrogen to waste1 thus 
enabling the farmer to put back into his
 soil most of the nitrogen which was    
extracted from it by his crops and then 
used by his stock4 ,his vegetable crops 
raise the nitrates into proteids4 ,his  
animals feed upon the proteids1 and     
perform his work or furnish him with    
milk4 ,then his bacteria stock take the 
excreted or refuse nitrogen1 and in his 
manure heap turn it back again into     
nitrates ready to begin the circle once 
more4 ,this might go on almost          
indefinitely were it not for two facts1 
the farmer sends nitrogenous material   
off his farm in the milk or grains or   
other nitrogenous products1 which he    
sells1 and the decomposition processes1 
as we have seen1 dissipate some of the  
nitrogen into the air as free nitrogen4 
,to meet this emergency and loss the    
farmer has another method of enriching  

the soil1 again depending upon bacteria4
 ,this is the so- called green manuring4
 ,here certain plants which seize       
nitrogen from the air are cultivated    
upon the field to be fertilized1 and1   
instead of harvesting a crop1 it is     
ploughed into the soil4 ,or perhaps the 
tops may be harvested1 the rest being   
ploughed into the soil4 ,the vegetable  
material thus ploughed in lies over a   
season and enriches the soil4 ,here the 
bacteria of the soil come into play in  
several directions4 ,first1 if the crop 
sowed be a legume1 the soil bacteria    
assist it to seize the nitrogen from the
 air4 ,the only plants which are of use 
in this green manuring are those which  
can1 through the agency of bacteria1    
obtain nitrogen from the air and store  
it in their roots4 ,second1 after the   
crop is ploughed into the soil various  
decomposing bacteria seize upon it1     
pulling the compounds to pieces4 ,the   
carbon is largely dissipated into the   
air as carbonic dioxide1 where the next 

generation of plants can get hold of it4
 ,the minerals and the nitrogen remain  
in the soil4 ,the nitrogenous portions  
go through the same series of           
decomposition and synthetical changes   
already described1 and thus eventually  
the nitrogen seized from the air by the 
combined action of the legumes and the  
bacteria is converted into nitrates1 and
 will serve for food for the next set of
 plants grown on the same soil4 ,here is
 thus a practical method of using the   
nitrogen assimilation powers of         
bacteria1 and reclaiming nitrogen from  
the air to replace that which has been  
lost4 ,thus it is that the farmer's     
nitrogen problem of the fertile soil    
appears to resolve itself into a proper 
handling of bacteria4 ,these organisms  
have stocked his soil in the first      
place4 ,they convert all of his compost 
heap wastes into simple bodies1 some of 
which are changed into plant foods1     
while others are at the same time lost4 
,lastly1 they may be made to reclaim    

this lost nitrogen1 and the fanner1 so  
soon as he has requisite knowledge of   
these facts1 will be able to keep within
 his control the supply of this         
important element4 ,the continued       
fertility of the soil is thus a gift    
from the bacteria4  ,,bacteria ,,as     
,,sources ,,of ,,trouble ,,to ,,the     
,,farmer4  ,while the topics already    
considered comprise the most important  
factors in agricultural bacteriology1   
the farmer's relations to bacteria do   
not end here4 ,these organisms come     
incidentally into his life in many ways4
 ,they are not always his aids as they  
are in most of the instances thus far   
cited4 ,they produce disease in his     
cattle1 as will be noticed in the next  
chapter4 ,bacteria are agents of        
decomposition1 and they are just as     
likely to decompose material which the  
farmer wishes to preserve as they are to
 decompose material which the farmer    
desires to undergo the process of decay4
 ,they are as ready to attack his fruits

 and vegetables as to ripen his cream4  
,the skin of fruits and vegetables is a 
moderately good protection of the       
interior from the attack of bacteria2   
but if the skin be broken in any place1 
bacteria get in and cause decay1 and to 
prevent it the farmer uses a cold       
cellar4 ,the bacteria prevent the farmer
 from preserving meats for any length of
 time unless he checks their growth in  
some way4 ,they get into the eggs of his
 fowls and ruin them4 ,their troublesome
 nature in the dairy in preventing the  
keeping of milk has already been        
noticed4 ,if he plants his seeds in very
 moist1 damp weather1 the soil bacteria 
cause too rapid a decomposition of the  
seeds and they rot in the ground instead
 of sprouting4 ,they produce            
disagreeable odours1 and are the cause  
of most of the peculiar smells1 good and
 bad1 around the barn4 ,they attack the 
organic matter which gets into his well 
or brook or pond1 decomposing it1       
filling the water with disagreeable and 

perhaps poisonous products which render 
it unfit to drink4 ,they not only aid in
 the decay of the fallen tree in his    
forests2 but in the same way attack the 
timber which he wishes to preserve1     
especially if it is kept in a moist     
condition4 ,thus they contribute largely
 to the gradual destruction of wooden   
structures4 ,it is therefore the        
presence of these organisms which forces
 him to dry his hay1 to smoke his hams1 
to corn his beef1 to keep his fruits and
 vegetables cool and prevent skin       
bruises1 to ice his dairy1 to protect   
his timber from rain1 to use stone      
instead of wooden foundations for       
buildings1 etc4 ,in general1 when the   
farmer desires to get rid of any organic
 refuse1 he depends upon bacteria1 for  
they are his sole agents 7aside from    
fire7 for the final destruction of      
organic matter4 ,when he wishes to      
convert waste organic refuse into       
fertilizing material1 he uses the       
bacteria of his compost heap4 ,on the   

other hand1 whenever he desires to      
preserve organic material1 the bacteria 
are the enemies against which he must   
carefully guard4  ,thus the farmer's    
life from year's end to year's end is in
 most intimate association with         
bacteria4 ,upon them he depends to      
insure the continued fertility of his   
soil and the constant continued         
production of good crops4 ,upon them he 
depends to turn into plant food all the 
organic refuse from his house or from   
his barn4 ,upon them he depends to      
replenish his stock of nitrogen4 ,it is 
these organisms which furnish his dairy 
with its butter flavours and with the   
taste of its cheese4 ,but1 on the other 
hand1 against them he must be constantly
 alert4 ,all his food products must be  
protected from their ravages4 ,a        
successful farmer's life1 then1 largely 
resolves itself into a skilful          
management of bacterial activity4 ,to   
aid them in destroying or decomposing   
everything which he does not desire to  

preserve1 and to prevent their          
destroying the organic material which he
 wishes to keep for future use1 is the  
object of a considerable portion of farm
 labour2 and the most successful farmer 
to-day1 and we believe the most         
successful farmer of the future1 is the 
one who most intelligently and skilfully
 manipulates these gigantic forces      
furnished him by the growth of his      
microscopical allies4  ,,relation ,,of  
,,bacteria ,,to ,,coal4 ,another one of 
,nature's processes in which bacteria   
have played an important part is in the 
formation of coal4 ,it is unnecessary to
 emphasize the importance of coal in    
modern civilization4 ,aside from its use
 as fuel1 upon which civilization is    
dependent1 coal is a source of an       
endless variety of valuable products4   
,it is the source of our illuminating   
gas1 and ammonia is one of the products 
of the gas manufacture4 ,from the coal  
also comes coal tar1 the material from  
which such a long series of valuable    

materials1 as aniline colours1 carbolic 
acid1 etc1 is derived4 ,the list of     
products which we owe to coal is very   
long1 and the value of this material is 
hardly to be overrated4 ,in the         
preparation of these ingredients from   
coal bacteria do not play any part4     
,most of them are derived by means of   
distillation4 ,but when asked for the   
agents which have given us the coal of  
the coal beds1 we shall find that here1 
too1 we owe a great debt to bacteria4   
,coal1 as is well known1 has come from  
the accumulation of the luxuriant       
vegetable growth of the past geological 
ages4 ,it has therefore been directly   
furnished us by the vegetation of the   
green plants of the past1 and1 in       
general1 it represents so much carbonic 
dioxide which these plants have         
extracted from the atmosphere4 ,but     
while the green plants have been the    
active agents in producing this         
assimilation1 bacteria have played an   
important part in coal manufacture in   

two different directions4 ,the first    
appears to be in furnishing these plants
 with nitrogen4 ,without a store of     
fixed nitrogen in the soil these        
carboniferous plants could not have     
grown4 ,this matter has already been    
considered4 ,we have no very absolute   
knowledge as to the agency of bacteria  
in furnishing nitrogen for this         
vegetation in past ages1 but there is   
every reason to believe that in the     
past1 as in the present1 the chief      
source of organic nitrogen has been from
 the atmosphere and derived from the    
atmosphere through the agency of        
bacteria4 ,in the absence of any other  
known factor we may be pretty safe in   
the assumption that bacteria played an  
important part in this nitrogen         
fixation1 and that bacteria must        
therefore be regarded as the agents     
which have furnished us the nitrogen    
stored in the coal4  ,but in a later    
stage of coal formation bacteria have   
contributed more directly to the        

formation of coal4 ,coal is not simply  
accumulated vegetation4 ,the coal of our
 coal beds is very different in its     
chemical composition from the wood of   
the trees4 ,it contains a much higher   
percentage of carbon and a lower        
percentage of hydrogen and oxygen than  
ordinary vegetable substances4 ,the     
conversion of the vegetation of the     
carboniferous ages into coal was        
accompanied by a gradual loss of        
hydrogen and a consequent increase in   
the percentage of carbon4 ,it is this   
change that has added to the density of 
the substance and makes the greater     
value of coal as fuel4 ,there is little 
doubt now as to the method by which this
 woody material of the past has been    
converted into coal4 ,the same process  
appears to be going on in a similar     
manner to-day in the peat beds of       
various northern countries4 ,the fallen 
vegetation1 trees1 trunks1 branches1 and
 leaves1 accumulate in masses1 and1 when
 the conditions of moisture and         

temperature are right1 begin to undergo 
a fermentation4 ,ordinarily this action 
of bacteria1 as already noticed1        
produces an almost complete though slow 
oxidation of the carbon1 and results in 
the total decay of the vegetable matter4
 ,but if the vegetable mass be covered  
by water and mud under proper conditions
 of moisture and temperature1 a         
different kind of fermentation arises   
which does not produce such complete    
decay4 ,the covering of water prevents  
the access of oxygen to the fermenting  
mass1 an oxidation of the carbon is     
largely prevented1 and the vegetable    
matter slowly changes its character4    
,under the influence of this slow       
fermentation1 aided1 probably by        
pressure1 the mass becomes more and more
 solid and condensed1 its woody         
character becomes less and less         
distinct1 and there is a gradual loss of
 the hydrogen and the oxygen4 ,doubtless
 there is a loss of carbon also1 for    
there is an evolution of marsh gas which

 contains carbon4 ,but1 in this slow    
fermentation taking place under the     
water in peat bogs and marshes the      
carbon loss is relatively small2 the    
woody material does not become          
completely oxidized1 as it does in free 
operations of decay4 ,the loss of       
hydrogen and oxygen from the mass is    
greater than that of carbon1 and the    
percentage of carbon therefore          
increases4 ,this is not the ordinary    
kind of fermentation that goes on in    
vegetable accumulations4 ,it requires   
special conditions and possibly special 
kinds of fermenting organisms4 ,peat is 
not formed in all climates4 ,in warm    
regions1 or where the woody matter is   
freely exposed to the air1 the          
fermentation of vegetable matter is more
 complete1 and it is entirely destroyed 
by oxidation4 ,it is only in colder     
regions and when covered with water that
 the destruction of the organic matter  
stops short of decay4 ,but such         
incomplete fermentation is still going  

on in many parts of the world1 and by   
its means vegetable accumulations are   
being converted into peat4  ,this       
formation of peat appears to be a first 
step in the formation of denser coal4   
,by a continuation of the same processes
 the mass becomes still more dense and  
solid4 ,as we pass from the top to the  
bottom of such an accumulation of peat1 
we find it becoming denser and denser1  
and at the bottom it is commonly of a   
hard consistence1 brownish in colour1   
and with only slight traces of the      
original woody structure4 ,such material
 is called lignite4 ,it contains a      
higher percentage of carbon than peat1  
but a lower percentage than coal1 and is
 plainly a step in coal formation4 ,but 
the process goes on1 the hydrogen and   
oxygen loss continuing until there is   
finally produced true coal4  ,if this is
 the correct understanding of the       
formation of coal1 we see that we have  
plainly a process in which bacterial    
life has had a large and important      

share4 ,we are1 of course1 densely      
ignorant of the exact processes going   
on4 ,we know nothing positively as to   
the kind of microorganisms which produce
 this slow1 peculiar fermentation4 ,as  
yet1 the fermentation going on in the   
formation of the peat has not been      
studied by the bacteriologists1 and we  
do not know from direct experiment that 
it is a matter of bacterial action4 ,it 
has been commonly regarded as simply a  
slow chemical change1 but its general   
similarity to other fermentative        
processes is so great that we can have  
little hesitation in attributing it to  
micro-organisms1 and doubtless to some  
forms of plants allied to bacteria4     
,there is no reason for doubting that   
bacteria existed in the geological ages 
with essentially the same powers as they
 now possess1 and to some forms of      
bacteria which grow in the absence of   
oxygen can we probably attribute the    
slow change which has produced coal4    
,here1 then1 is another great source of 

wealth in ,nature for which we are      
dependent upon bacteria4 ,while1 of     
course1 water and pressure were very    
essential factors in the deposition of  
coal1 it was a peculiar kind of         
fermentation occurring in the vegetation
 that brought about the chemical changes
 in it which resulted in its            
transformation into coal4 ,the          
vegetation of the carboniferous age was 
dependent upon the nitrogen fixed by the
 bacteria1 and to these organisms also  
do we owe the fact that this vegetation 
was stored for us in the rocks4         
,,chapter ,v4  ,,parasitic ,,bacteria   
,,and ,,their ,,relation ,,to ,,disease4
   ,perhaps the most universally known  
fact in regard to bacteria is that they 
are the cause of disease4 ,it is this   
fact that has made them objects of such 
wide interest4 ,this is the side of the 
subject that first attracted attention1 
has been most studied1 and in regard to 
which there has been the greatest       
accumulation of evidence4 ,so           

persistently has the relation of        
bacteria to disease been discussed and  
emphasized that the majority of readers 
are hardly able to disassociate the two4
 ,to most people the very word bacteria 
is almost equivalent to disease1 and the
 thought of swallowing microbes in      
drinking water or milk is decidedly     
repugnant and alarming4 ,in the public  
mind it is only necessary to demonstrate
 that an article holds bacteria to throw
 it under condemnation4  ,we have       
already seen that bacteria are to be    
regarded as agents for good1 and that   
from their fundamental relation to plant
 life they must be looked upon as our   
friends rather than as our enemies4 ,it 
is true that there is another side to   
the story which relates to the parasitic
 species4 ,these parasitic forms may do 
us direct or indirect injury4 ,but the  
species of bacteria which are capable of
 doing us any injury1 the pathogenic    
bacteria1 are really very few compared  
to the great host of species which are  

harmless4 ,a small number of species1   
perhaps a score or two1 are pathogenic1 
while a much larger number1 amounting to
 hundreds and perhaps thousands of      
species1 are perfectly harmless4 ,this  
latter class do no injury even though   
swallowed by man in thousands4 ,they are
 not parasitic1 and are unable to grow  
in the body of man4 ,their presence is  
entirely consistent with the most       
perfect health1 and1 indeed1 there are  
some reasons for believing that they are
 sometimes directly beneficial to       
health4 ,it is entirely unjust to       
condemn all bacteria because a few      
chance to produce mischief4 ,bacteria in
 general are agents for good rather than
 ill4  ,there are1 however1 some species
 which cause mankind much trouble by    
interfering in one way or another with  
the normal processes of life4 ,these    
pathogenic bacteria1 or disease germs1  
do not all act alike1 but bring about   
injury to man in a number of different  
ways4 ,we may recognise two different   

classes among them1 which1 however1 we  
shall see are connected by intermediate 
types4 ,these two classes are1 first1   
the pathogenic bacteria1 which are not  
strictly parasitic but live free in     
,nature2 and1 second1 those which live  
as true parasites in the bodies of man  
or other animals4 ,to understand the    
real relation of these two classes1 we  
must first notice the method by which   
bacteria in general produce disease4    
,,method ,,by ,,which ,,bacteria        
,,produce ,,disease4  ,since it was     
first clearly recognised that certain   
species of bacteria have the power of   
producing disease1 the question as to   
how they do so has ever been a prominent
 one ,even if they do grow in the body1 
why should their presence give rise to  
the symptoms characterizing disease8    
,various answers to this question have  
been given in the past ,it has been     
suggested that in their growth they     
consume the food of the body and thus   
exhaust it1 that they produce an        

oxidation of the body tissues1 or that  
they produce a reduction of these       
tissues1 or that they mechanically      
interfere with the circulation ,none of 
these suggestions have proved of much   
value ,another view was early advanced1 
and has stood the test of time4 ,this   
claim is that the bacteria while growing
 in the body produce poisons1 and these 
poisons then have a direct action on the
 body ,we have already noticed that     
bacteria during their growth in any     
medium produce a large number of        
biproducts of decomposition4 ,we noticed
 also that among these biproducts there 
are some which have a poisonous nature2 
so poisonous are they that when         
inoculated into the body of an animal   
they may produce poisoning and death4   
,we have only to suppose that the       
pathogenic bacteria1 when growing as    
parasites in man1 produce such poisons1 
and we have at once an explanation of   
the method by which they give rise to   
disease4  ,this explanation of germ     

disease is more than simple theory4 ,it 
has been in many cases clearly          
demonstrated4 ,it has been found that   
the bacteria which cause diphtheria1    
tetanus1 typhoid1 tuberculosis1 and many
 other diseases1 produce1 even when     
growing in common culture media1 poisons
 which are of a very violent nature4    
,these poisons when inoculated into the 
bodies of animals give rise to much the 
same symptoms as the bacteria do        
themselves when growing as parasites in 
the animals4 ,the chief difference in   
the results from inoculating an animal  
with the poison and with the living     
bacteria is in the rapidity of the      
action4 ,when the poison is injected the
 poisoning symptoms are almost          
immediately seen1 but when the living   
bacteria are inoculated the effect is   
only seen after several days or longer1 
not1 in short1 until the inoculated     
bacteria have had time enough to grow in
 the body and produce the poison in     
quantity4 ,it has not by any means been 

shown that all pathogenic germs produce 
their effect in this way1 but it has    
been proved to be the real method in    
quite a number of cases1 and is         
extremely probable in others4 ,while    
some bacteria perhaps produce results by
 a different method1 we must recognise  
the production of poisons as at all     
events the common direct cause of the   
symptoms of disease4 ,this explanation  
will enable us more clearly to          
understand the relation of different    
bacteria to disease4  ,,pathogenic      
,,germs ,,which ,,are ,,not ,,strictly  
,,parasitic  ,recognising that bacteria 
may produce poisons1 we readily see that
 it is not always necessary that they   
should be parasites in order to produce 
trouble4 ,in their ordinary growth in   
,nature such bacteria will produce no   
trouble ,the poisons will be produced in
 decaying material but will seldom be   
taken into the human body4 ,these       
poisons1 produced in the first stages of
 putrefaction1 are oxidized by further  

stages of decomposition into harmless   
products4 ,but should it happen that    
some of these bacteria obtained a chance
 to grow vigorously for a while in      
organic products that are subsequently  
swallowed as man's food1 it is plain    
that evil results might follow4 ,if such
 food is swallowed by man after the     
bacteria have produced their poisonous  
bodies1 it will tend to produce an      
immediate poisoning of his system4 ,the 
effect may be sudden and severe if      
considerable quantity of the poisonous  
material is swallowed1 or slight but    
protracted if small quantities are      
repeatedly consumed in food4 ,such      
instances are not uncommon4 ,well-known 
examples are cases of ice-cream         
poisoning1 poisoning from eating cheese 
or from drinking milk1 or in not a few  
instances from eating fish or meats     
within which bacteria have had          
opportunity for growth4 ,in all these   
cases the poison is swallowed in        
quantity sufficient to give rise quickly

 to severe symptoms1 sometimes resulting
 fatally1 and at other times passing off
 as soon as the body succeeds in        
throwing off the poisons4 ,in other     
cases still1 however1 the amount of     
poison swallowed may be very slight1 too
 slight to produce much effect unless   
the same be consumed repeatedly4 ,all   
such trouble may be attributed to       
fermented or partly decayed food4 ,it is
 difficult to distinguish such instances
 from others produced in a slightly     
different way1 as follows3  ,it may     
happen that the bacteria which grow in  
food products continue to grow in the   
food even after it is swallowed and has 
passed into the stomach or intestines4  
,this appears particularly true of milk 
bacteria4 ,under these conditions the   
bacteria are not in any proper sense    
parasitic1 since they are simply living 
in and feeding upon the same food which 
they consume outside the body1 and are  
not feeding upon the tissues of man4    
,the poisons which they produce will    

continue to be developed as long as the 
bacteria continue to grow1 whether in a 
milk pail or a human stomach4 ,if now   
the poisons are absorbed by the body1   
they may produce a mild or severe       
disease which will be more or less      
lasting1 continuing perhaps as long as  
the same food and the same bacteria are 
supplied to the individual4 ,the most   
important disease of this class appears 
to be the dreaded cholera infantum1 so  
common among infants who feed upon cow's
 milk in warm weather4 ,it is easy to   
understand the nature of this disease   
when we remember the great number of    
bacteria in milk1 especially in hot     
weather1 and when we remember that the  
delicate organism of the infant will be 
thrown at once into disorder by slight  
amounts of poison which would have no   
appreciable effect upon the stronger    
adult4 ,we can easily understand1       
further1 how the disease readily yields 
to treatment if care is taken to        
sterilize the milk given to the patient4

  ,we do not know to-day the extent of  
the troubles which are produced by      
bacteria of this sort4 ,they will1 of   
course1 be chiefly connected with our   
food products1 and commonly1 though not 
always1 will affect the digestive       
functions4 ,it is probable that many of 
the cases of summer diarrhoea are       
produced by some such cause1 and if they
 could be traced to their source would  
be found to be produced by bacterial    
poisons swallowed with food or drink1 or
 by similar poisons produced by bacteria
 growing in such food after it is       
swallowed by the individual4 ,in hot    
weather1 when bacteria are so abundant  
everywhere and growing so rapidly1 it is
 impossible to avoid such dangers       
completely without exercising over all  
food a guard which would be decidedly   
oppressive4 ,it is well to bear in mind1
 however1 that the most common and most 
dangerous source of such poisons is milk
 or its products1 and for this reason   
one should hesitate to drink milk in hot

 weather unless it is either quite fresh
 or has been boiled to destroy its      
bacteria4  ,,pathogenic ,,bacteria      
,,which ,,are ,,true ,,parasites4  ,this
 class of pathogenic bacteria includes  
those which actually invade the body and
 feed upon its tissues instead of living
 simply upon swallowed food4 ,it is     
difficult1 however1 to draw any sharp   
line separating the two classes4 ,the   
bacteria which cause diphtheria 7,fig4  
#bh71 for instance1 do not really invade
 the body4 ,they grow in the throat1    
attached to its walls1 and are confined 
to this external location or to the     
superficial tissues4 ,this bacillus is1 
in short1 only found in the mouth and   
throat1 and is practically confined to  
the so-called false membranes4 ,it never
 enters any of the tissues of the body1 
although attached to the mucous         
membrane4 ,it grows vigorously in this  
membrane1 and there secretes or in some 
way produces extremely violent poisons4 
,these poisons are then absorbed by the 

body and give rise to the general       
symptoms of the disease4 ,much the same 
is true of the bacillus which causes    
tetanus or lockjaw 7,fig4 #bi74 ,this   
bacillus is commonly inoculated into the
 flesh of the victim by a wound made    
with some object which has been lying   
upon the earth where the bacillus lives4
 ,the bacillus grows readily after being
 inoculated1 but it is localized at the 
point of the wound1 without invading the
 tissue to any extent4 ,it produces1    
however1 during its growth several      
poisons which have been separated and   
studied4 ,among them are some of the    
most violent poisons of which we have   
any knowledge4 ,while the bacillus grows
 in the tissues around the wound it     
secretes these poisons1 which are then  
absorbed by the body generally4 ,their  
poisoning effects produce the violent   
symptoms of the disease4 ,of much the   
same nature is ,asiatic cholera4 ,this  
is caused by a bacillus which is able to
 grow rapidly in the intestines1 feeding

 perhaps in part on the food in the     
intestines and perhaps in part upon the 
body secretions4 ,to a slight extent    
also it appears to be able to invade the
 tissues of the body1 for the bacilli   
are found in the walls of the           
intestines4 ,but it is not a proper     
parasite1 and the fatal disease it      
produces is the result of the absorption
 of the poisons secreted in the         
intestines4  ,it is but a step from this
 to the true parasites4 ,typhoid fever1 
for example1 is a disease produced by   
bacteria which grow in the intestines1  
but which also invade the tissues more  
extensively than the cholera germs      
7,fig4 #cj74 ,they do not invade the    
body generally1 however1 but become     
somewhat localized in special glands    
like the liver1 the spleen1 etc4 ,even  
here they do not appear to find a very  
favourable condition1 for they do not   
grow extensively in these places4 ,they 
are likely to be found in the spleen in 
small groups or centres1 but not        

generally distributed through it4       
,wherever they grow they produce poison1
 which has been called typhotoxine1 and 
it is this poison chiefly which gives   
rise to the fever4  ,quite a            
considerable number of the pathogenic   
germs are1 like the typhoid bacillus1   
more or less confined to special places4
 ,instead of distributing themselves    
through the body after they find        
entrance1 they are restricted to special
 organs4 ,the most common example of a  
parasite of this sort is the            
tuberculosis bacillus1 the cause of     
consumption1 scrofula1 white swelling1  
lupus1 etc4 7,fig4 #ca74 ,although this 
bacillus is very common and is able to  
attack almost any organ in the body1 it 
is usually very restricted in growth4   
,it may become localized in a small     
gland1 a single joint1 a small spot in  
the lungs1 or in the glands of the      
mesentery1 the other parts of the body  
remaining free from infection4 ,not     
infrequently the whole trouble is thus  

confined to such a small locality that  
nothing serious results4 ,but in other  
instances the bacilli may after a time  
slowly or rapidly distribute themselves 
from these centres1 attacking more and  
more of the body until perhaps fatal    
results follow in the end4 ,this disease
 is therefore commonly of very slow     
progress4  ,again1 we have still other  
parasites which are not thus confined1  
but which1 as soon as they enter the    
body1 produce a general infection1      
attacking the blood and perhaps nearly  
all tissues simultaneously4 ,the most   
typical example of this sort is anthrax 
or malignant pustule1 a disease         
fortunately rare in man 7,fig4 #cb74    
,here the bacilli multiply in the blood1
 and very soon a general and fatal      
infection of the whole body arises1     
resulting from the abundance of the     
bacilli everywhere4 ,some of the obscure
 diseases known as blood poisoning      
appear to be of the same general nature1
 these diseases resulting from a very   

general invasion of the whole body by   
certain pathogenic bacteria4  ,in       
general1 then1 we see that the so-called
 germ diseases result from the action   
upon the body of poisons produced by    
bacterial growth4 ,differences in the   
nature of these poisons produce         
differences in the character of the     
disease1 and differences in the         
parasitic powers of the different       
species of bacteria produce wide        
differences in the course of the        
diseases and their relation to external 
phenomena4  ,,what ,,diseases ,,are     
,,due ,,to ,,bacteria8  ,it is1 of      
course1 an extremely important matter to
 determine to what extent human diseases
 are caused by bacteria4 ,it is not     
easy1 nor indeed possible1 to do this   
to-day with accuracy4 ,it is no easy    
matter to prove that any particular     
disease is caused by bacteria4 ,to do   
this it is necessary to find some       
particular bacterium present in all     
cases of the disease2 to find some      

method of getting it to grow outside the
 body in culture media2 to demonstrate  
its absence in healthy animals1 or      
healthy human individuals if it be a    
human disease2 and1 finally1 to         
reproduce the disease in healthy animals
 by inoculating them with the bacterium4
 ,all of these steps of proof present   
difficulties1 but especially the last   
one4 ,in the study of animals it is     
comparatively easy to reproduce a       
disease by inoculation4 ,but experiments
 upon man are commonly impossible1 and  
in the case of human diseases it is     
frequently very difficult or impossible 
to obtain the final test of the matter4 
,after finding a specific bacterium     
associated with a disease1 it is usually
 possible to experiment with it further 
upon animals only4 ,but some human      
diseases do not attack animals1 and in  
the case of diseases that may be given  
to animals it is frequently uncertain   
whether the disease produced in the     
animal by such inoculation is identical 

with the human disease in question1     
owing to the difference of symptoms in  
the different animals4 ,as a            
consequence1 the proof of the germ      
nature of different diseases varies all 
the way from absolute demonstration to  
mere suspicion4 ,to give a complete and 
correct list of the diseases caused by  
bacteria1 or to give a list of the      
bacteria species pathogenic to man1 is  
therefore at present impossible4  ,the  
difficulty of giving such a list is     
rendered greater from the fact that we  
have in recent years learned that the   
same species of pathogenic bacterium may
 produce different results under        
different conditions4 ,when the subject 
of germ disease was first studied and   
the connection between bacteria and     
disease was first demonstrated1 it was  
thought that each particular species of 
pathogenic bacteria produced a single   
definite disease2 and conversely1 each  
germ disease was supposed to have its   
own definite species of bacterium as its

 cause4 ,recent study has shown1        
however1 that this is not wholly true4  
,it is true that some diseases do have  
such a definite relation to definite    
bacteria4 ,the anthrax germ1 for        
example1 will always produce anthrax1 no
 matter where or how it is inoculated   
into the body4 ,so1 also1 in quite a    
number of other cases distinct specific 
bacteria are associated with distinct   
diseases4 ,but1 on the other hand1 there
 are some pathogenic bacteria which are 
not so definite in their action1 and    
produce different results in accordance 
with circumstances1 the effect varying  
both with the organ attacked and with   
the condition of the individual4 ,for   
instance1 a considerable number of      
different types of blood poisoning1     
septicaemia1 pyaemia1 gangrene1         
inflammation of wounds1 or formation of 
pus from slight skin wounds--indeed1 a  
host of miscellaneous troubles1 ranging 
all the way from a slight pus formation 
to a violent and severe blood           

poisoning--all appear to be caused by   
bacteria1 and it is impossible to make  
out any definite species associated with
 the different types of these troubles4 
,there are three common forms of        
so-called pus cocci1 and these are found
 almost indiscriminately with various   
types of inflammatory troubles4         
,moreover1 these species of bacteria are
 found with almost absolute constancy in
 and around the body1 even in health4   
,they are on the clothing1 on the skin1 
in the mouth and alimentary canal4 ,here
 they exist1 commonly doing no harm4    
,they have1 however1 the power of doing 
injury if by chance they get into       
wounds4 ,but their power of doing injury
 varies both with the condition of the  
individual and with variations in the   
bacteria themselves4 ,if the individual 
is in a good condition of health these  
bacteria have little power of injuring  
him even when they do get into such     
wounds1 while at times of feeble        
vitality they may do much more injury1  

and take the occasion of any little cut 
or bruise to enter under the skin and   
give rise to inflammation and pus4 ,some
 people will develop slight abscesses or
 slight inflammations whenever the skin 
is bruised1 while with others such      
bruises or cuts heal at once without    
trouble4 ,both are doubtless subject to 
the same chance of infection1 but the   
one resists1 while the other does not4  
,in common parlance1 we say that such a 
tendency to abscesses indicates a bad   
condition of the blood--a phrase which  
means nothing4 ,further1 we find that   
the same species of bacterium may have  
varying powers of producing disease at  
different times4 ,some species are      
universal inhabitants of the alimentary 
canal and are ordinarily harmless1 while
 under other conditions of unknown      
character they invade the tissues and   
give rise to a serious and perhaps fatal
 disease4 ,we may thus recognise some   
bacteria which may be compared to       
foreign invaders1 while others are      

domestic enemies4 ,the former1 like the 
typhoid bacillus1 always produce trouble
 when they succeed in entering the body 
and finding a foothold4 ,the latter1    
like the normal intestinal bacilli1 are 
always present but commonly harmless1   
only under special conditions becoming  
troublesome4 ,all this shows that there 
are other factors in determining the    
course of a disease1 or even the        
existence of a disease1 than the simple 
presence of a peculiar species of       
pathogenic bacterium4  ,from the facts  
just stated it will be evident that any 
list of germ diseases will be rather    
uncertain4 ,still1 the studies of the   
last twenty years or more have disclosed
 some definite relations of bacteria and
 disease1 and a list of the diseases    
more or less definitely associated with 
distinct species of bacteria is of      
interest4 ,such a list1 including only  
well-known diseases1 is as follows3     
,name of disease4              ,name of 
bacterium producing the disease4        

,anthrax 7,malignant pustule74          
,bacillus anthracis4  ,cholera4         
,spirillum cholera3 asiaticae  ,croupous
 pneumonia4              ,micrococcus   
pneumonia crouposa4  ,diphtheria4       
,bacillus diphtheria4  ,glanders4       
,bacillus mallei4  ,gonorrhoea4         
,micrococcus gonorrhaeae  ,influenza4   
,bacillus of influenza4  ,leprosy4      
,bacillus leprae4  ,relapsing fever4    
,spirillum ,obermeieri4  ,tetanus       
7lockjaw74               ,bacillus      
tetani4  ,tuberculosis 7including       
consumption1 scrofula1 etc47            
,bacillus tuberculosis4  ,typhoid fever4
                   ,bacillus typhi      
abdominalis4  ,various wound infections1
 including septicaemia1 pyaemia1 acute  
abscesses1 ulcers1 erysipelas1 etc41 are
 produced by a few forms of micrococci1 
resembling each other in many points but
 differing slightly4 ,they are found    
almost indiscriminately in any of these 
wound infections1 and none of them      
appears to have any definite relation to

 any special form of disease unless it  
be the micrococcus of erysipelas4 ,the  
common pus micrococci are grouped under 
three species1 ,staphylococcus pyogenes 
aureus1 ,staphylococcus pyogenes1 and   
,streptococcus pyogenes4 ,these three   
are the most common1 but others are     
occasionally found4  ,in addition to    
these1 which may be regarded as         
demonstrated1 the following diseases are
 with more or less certainty regarded as
 caused by distinct specific bacteria3  
,bronchitis1 endocarditis1 measles1     
whooping-cough1 peritonitis1 pneumonia1 
syphilis4  ,still another list might be 
given of diseases whose general nature  
indicates that they are caused by       
bacteria1 but in connection with which  
no distinct bacterium has yet been      
found4 ,as might be expected also1 a    
larger list of animal diseases has been 
demonstrated to be caused by these      
organisms4 ,in addition1 quite a number 
of species of bacteria have been found  
in such material as faeces1 putrefying  

blood1 etc41 which have been shown by   
experiment to be capable of producing   
diseases in animals1 but in regard to   
which we have no evidence that they ever
 do produce actual disease under any    
normal conditions4 ,these may           
contribute1 perhaps1 to the troubles    
arising from poisonous foods1 but can   
not be regarded as disease germs proper4
  ,,variability ,,of ,,pathogenic       
,,powers4  ,as has already been stated1 
our ideas of the relation of bacteria to
 disease have undergone quite a change  
since they were first formulated1 and we
 recognise other factors influencing    
disease besides the actual presence of  
the bacterium4 ,these we may briefly    
consider under two heads1 viz41         
variation in the bacterium1 and         
variation in the susceptibility of the  
individual4 ,the first will require only
 a brief consideration4  ,that the same 
species of pathogenic bacteria at       
different times varies in its powers to 
produce disease has long been known4    

,various conditions are known to affect 
thus the virulence of bacteria4 ,the    
bacillus which is supposed to give rise 
to pneumonia loses its power to produce 
the disease after having been cultivated
 for a short time in ordinary culture   
media in the laboratory4 ,this is easily
 understood upon the suggestion that it 
is a parasitic bacillus and does not    
thrive except under parasitic           
conditions4 ,its pathogenic powers can  
sometimes be restored by passing it     
again through some susceptible animal4  
,one of the most violent pathogenic     
bacteria is that which produces anthrax1
 but this loses its pathogenic powers if
 it is cultivated for a considerable    
period at a high temperature4 ,the      
micrococcus which causes fowl cholera   
loses its power if it be cultivated in  
common culture media1 care being taken  
to allow several days to elapse between 
the successive inoculations into new    
culture flasks4 ,most pathogenic        
bacteria can in some way be so treated  

as to suffer a diminution or complete   
loss of their powers of producing a     
fatal disease4 ,on the other hand1 other
 conditions will cause an increase in   
the virulence of a pathogenic germ4 ,the
 virus which produces hydrophobia is    
increased in violence if it is          
inoculated into a rabbit and            
subsequently taken from the rabbit for  
further inoculation4 ,the fowl cholera  
micrococcus1 which has been weakened as 
just mentioned1 may be restored to its  
original violence by inoculating it into
 a small bird1 like a sparrow1 and      
inoculating a second bird from this4 ,a 
few such inoculations will make it as   
active as ever4 ,these variations       
doubtless exist among the species in    
,nature as well as in artificial        
cultures4 ,the bacteria which produce   
the various wound infections and        
abscesses1 etc41 appear to vary under   
normal conditions from a type capable of
 producing violent and fatal blood      
poisoning to a type producing only a    

simple abscess1 or even to a type that  
is entirely innocuous4 ,it is this      
factor1 doubtless1 which in a large     
measure determines the severity of any  
epidemic of a bacterial contagious      
disease4  ,,susceptibility ,,of ,,the   
,,individual4  ,the very great          
modification of our early views has     
affected our ideas as to the power which
 individuals have of resisting the      
invasion of pathogenic bacteria4 ,it has
 from the first been understood that    
some individuals are more susceptible to
 disease than others1 and in attempting 
to determine the significance of this   
fact many valuable and interesting      
discoveries have been made4 ,after the  
exposure to the disease there follows a 
period of some length in which there are
 no discernible effects4 ,this is       
followed by the onset of the disease and
 its development to a crisis1 and1 if   
this be passed1 by a recovery4 ,the     
general course of a germ disease is     
divided into three stages3 the stage of 

incubation1 the development of the      
disease1 and the recovery4 ,the         
susceptibility of the body to a disease 
may be best considered under the three  
heads of ,invasion1 ,resistance1        
,recovery4  ,means of ,invasion4--,in   
order that a germ disease should arise  
in an individual1 it is first necessary 
that the special bacterium which causes 
the disease should get into the body4   
,there are several channels through     
which bacteria can thus find entrance2  
these are through the mouth1 through the
 nose1 through the skin1 and            
occasionally through excretory ducts4   
,those which come through the mouth come
 with the food or drink which we        
swallow2 those which enter through the  
nose must be traced to the air2 and     
those which enter through the skin come 
in most cases through contact with some 
infected object1 such as direct contact 
with the body of an infected person or  
his clothing or some objects he has     
handled1 etc4 ,occasionally1 perhaps1   

the bacteria may get into the skin from 
the air1 but this is certainly uncommon 
and confined to a few diseases4 ,there  
are here two facts of the utmost        
importance for every one to understand3 
first1 that the chance of disease       
bacteria being carried to us through the
 air is very slight and confined to a   
few diseases1 such as smallpox1         
tuberculosis1 scarlet fever2 etc41 and1 
secondly1 that the uninjured skin and   
the uninjured mucous membrane also is   
almost a sure protection against the    
invasion of the bacteria4 ,if the skin  
is whole1 without bruises or cuts1      
bacteria can seldom1 if ever1 find      
passage through it4 ,these two facts are
 of the utmost importance1 since of all 
sources of infection we have the least  
power to guard against infection through
 the air1 and since of all means 'of    
entrance we can guard the skin with the 
greatest difficulty4 ,we can easily     
render food free from pathogenic        
bacteria by heating it4 ,the material we

 drink can similarly be rendered        
harmless1 but we can not by any known   
means avoid breathing air1 nor is there 
any known method of disinfecting the    
air1 and it is impossible for those who 
have anything to do with sick persons to
 avoid entirely having contact either   
with the patient or with infected       
clothing or utensils4  ,from the facts  
here given it will be seen that the     
individual's susceptibility to disease  
produced by parasitic bacteria will     
depend upon his habits of cleanliness1  
his care in handling infectious         
material1 or care in cleansing the hands
 after such handling1 upon his habit of 
eating food cooked or raw1 and upon the 
condition of his skin and mucous        
membranes1 since any kind of bruises    
will increase susceptibility4 ,slight   
ailments1 such as colds1 which inflame  
the mucous membrane1 will decrease its  
resisting power and render the          
individual more susceptible to the      
entrance of any pathogenic germs should 

they happen to be present4 ,sores in the
 mouth or decayed teeth may in the same 
way be prominent factors in the         
individual's susceptibility4 ,thus quite
 a number of purely physical factors may
 contribute to an individual's          
susceptibility4  ,resisting ,power of   
the ,body4--,even after the bacteria get
 into the body it is by no means certain
 that they will give rise to disease1   
for they have now a battle to fight     
before they can be sure of holding their
 own4 ,it is now1 indeed1 that the      
actual conflict between the powers of   
the body and these microscopic invaders 
begins4 ,after they have found entrance 
into the body the bacteria have arrayed 
against them strong resisting forces of 
the human organism1 endeavouring to     
destroy and expel them4 ,many of them   
are rapidly killed1 and sometimes they  
are all destroyed without being able to 
gain a foothold4 ,in such cases1 of     
course1 no trouble results4 ,in other   
cases the body fails to overcome the    

powers of the invaders and they         
eventually multiply rapidly4 ,in this   
struggle the success of the invaders is 
not necessarily a matter of numbers4    
,they are simply struggling to gain a   
position in the body1 where they can    
feed and grow4 ,a few individuals may be
 entirely sufficient to seize such a    
foothold1 and then these by multiplying 
may soon become indefinitely numerous4  
,to protect itself1 therefore1 the human
 body must destroy every individual     
bacterium1 or at least render them all  
incapable of growth4 ,their marvellous  
reproductive powers give the bacteria an
 advantage in the battle4 ,on the other 
hand1 it takes time even for these      
rapidly multiplying beings to become    
sufficiently numerous to do injury4     
,there is thus an interval after their  
penetration into the body when these    
invaders are weak in numbers4 ,during   
this interval--the period of            
incubation--the body may organize a     
resistance sufficient to expel them4    

,we do not as yet thoroughly understand 
the forces which the human organism is  
able to array against these invading    
foes4 ,some of its methods of defence   
are1 however1 already intelligible to   
us1 and we know enough1 at all events1  
to give us an idea of the intensity of  
the conflict that is going on1 and of   
the vigorous and powerful forces which  
the human organism is able to bring     
against its invading enemies4  ,in the  
first place1 we notice that a majority  
of bacteria are utterly unable to grow  
in the human body even if they do find  
entrance4 ,there are known to           
bacteriologists to-day many hundreds1   
even thousands of species1 but the vast 
majority of these find in the human     
tissues conditions so hostile to their  
life that they are utterly unable to    
grow therein4 ,human flesh or human     
blood will furnish excellent food for   
them if the individual be dead1 but     
living human flesh and blood in some way
 exerts a repressing influence upon them

 which is fatal to the growth of a vast 
majority of species4 ,some few species1 
however1 are not thus destroyed by the  
hostile agencies of the tissues of the  
animal1 but are capable of growing and  
multiplying in the living body4 ,these  
alone are what constitute the pathogenic
 bacteria1 since1 of course1 these are  
the only bacteria which can produce     
disease by growing in the tissues of an 
animal4 ,the fact that the vast majority
 of bacteria can not grow in the living 
organism shows clearly enough that there
 are some conditions existing in the    
living tissue hostile to bacterial life4
 ,there can be little doubt1 moreover1  
that it is these same hostile           
conditions1 which enable the body to    
resist the attack of the pathogenic     
species in cases where resistance is    
successfully made4  ,what are the forces
 arrayed against these invaders8 ,the   
essential nature of the battle appears  
to be a production of poisons and       
counter poisons4 ,it appears to be an   

undoubted fact that the first step in   
repelling these bacteria is to flood    
them with certain poisons which check   
their growth4 ,in the blood and lymph of
 man and other animals there are present
 certain products which have a direct   
deleterious influence upon the growth of
 micro-organisms4 ,the existence of     
these poisons is undoubted1 many an     
experiment having directly attested to  
their presence in the blood of animals4 
,of their nature we know very little1   
but of their repressing influence upon  
bacterial growth we are sure4 ,they have
 been named alexines1 and they are      
produced in the living tissue1 although 
as to the method of their production we 
are in ignorance4 ,by the aid of these  
poisons the body is able to prevent the 
growth of the vast majority of bacteria 
which get into its tissues4 ,ordinary   
micro-organisms are killed at once1 for 
these alexines act as antiseptics1 and  
common bacteria can no more grow in the 
living body than they could in a        

solution containing other poisons ,thus 
the body has a perfect protection       
against the majority of bacteria4 ,the  
great host of species which are found in
 water1 milk1 air1 in our mouths or     
clinging to our skin1 and which are     
almost omnipresent in ,nature1 are      
capable of growing well enough in       
ordinary lifeless organic foods1 but    
just as soon as they succeed in finding 
entrance into living human tissue their 
growth is checked at once by these      
antiseptic agents which are poured upon 
them4 ,such bacteria are therefore not  
pathogenic germs1 and not sources of    
trouble to human health4  ,there are1 on
 the other hand1 a few species of       
bacteria which may be able to retain    
their lodgment in the body m spite of   
this attempt of the individual to get   
rid of them4 ,these1 of course1         
constitute the pathogenic species1 or so
 called disease germs4 ,only such       
species as can overcome this first      
resistance can be disease germs1 for    

they alone can retain their foothold in 
the body4  ,but how do these species    
overcome the poisons1 which kill the    
other harmless bacteria8 ,they1 as well 
as the harmless forms1 find these       
alexines injurious to their growth1 but 
in some way they are able to counteract 
the poisons4 ,in this general discussion
 of poisons we are dealing with a       
subject which is somewhat obscure1 but  
apparently the pathogenic bacteria are  
able to overcome the alexines of the    
body by producing in their turn certain 
other products which neutralize the     
alexines1 thus annulling their action4  
,these pathogenic bacteria1 when they   
get into the body1 give rise at once to 
a group of bodies which have been named 
lysines4 ,these lysines are as          
mysterious to us as the alexines1 but   
they neutralize the effect of the       
alexines and thus overcome the          
resistance the body offers to bacterial 
growth ,the invaders can now multiply   
rapidly enough to get a lasting foothold

 in the body and then soon produce the  
abnormal symptoms which we call disease 
,pathogenic bacteria thus differ from   
the non-pathogenic bacteria primarily in
 this power of secreting products which 
can neutralize the ordinary effects of  
the alexines1 and so overcome the body's
 normal resistance to their parasitic   
life4  ,even if the bacteria do thus    
overcome the alexines the battle is not 
yet over1 for the individual has another
 method of defence which is now brought 
into activity to check the growth of the
 invading organisms4 ,this second method
 of resistance is by means of a series  
of active cells found in the blood1     
known as white blood-corpuscles 7,fig4  
#cc a1 b74 ,they are minute bits of     
protoplasm present in the blood and     
lymph in large quantities4 ,they are    
active cells1 capable of locomotion and 
able to crawl out of the blood-vessels  
,not infrequently they are found to take
 into their bodies small objects with   
which they come in contact4 ,one of     

their duties is thus to engulf minute   
irritating bodies which may be in the   
tissues1 and to carry them away for     
excretion4 ,they thus act as scavengers 
,these corpuscles certainly have some   
agency in warding off the attacks of    
pathogenic bacteria ,very commonly they 
collect in great numbers in the region  
of the body where invading bacteria are 
found4 ,such invading bacteria exist    
upon them a strong attraction1 and the  
corpuscles leave the blood-vessels and  
sometimes form a solid phalanx          
completely surrounding the invading     
germs4 ,their collection at these points
 may make itself seen externally by the 
phenomenon we call inflammation4  ,there
 is no question that the corpuscles     
engage in conflict with the bacteria    
when they thus surround them4 ,there has
 been not a little dispute1 however1 as 
to the method by which they carry on the
 conflict4 ,it has been held by some    
that the corpuscles actually take the   
bacteria into their bodies1 swallow     

them1 as it were1 and subsequently      
digest them 7,fig4 #cc c1 d1 e74 ,this  
idea gave rise to the theory of         
phagocytosis1 and the corpuscles were   
consequently named phagocytes4 ,the     
study of several years has1 however1    
made it probable that this is not the   
ordinary method by which the corpuscles 
destroy the bacteria4 ,according to our 
present knowledge the method is a       
chemical one4 ,these cells1 when they   
thus collect in quantities around the   
invaders1 appear to secrete from their  
own bodies certain injurious products   
which act upon the bacteria much as do  
the alexines already mentioned4 ,these  
new bodies have a decidedly injurious   
effect upon the multiplying bacteria2   
they rapidly check their growth1 and1   
acting in union with the alexines1 may  
perhaps entirely destroy them4  ,after  
the bacteria are thus killed1 the white 
blood-corpuscles may load themselves    
with their dead bodies and carry them   
away 7,fig4 #cc d1 e74 ,sometimes they  

pass back into the blood stream and     
carry the bacteria to various parts of  
the body for elimination4 ,not          
infrequently the white corpuscles die in
 the contest1 and then may accumulate in
 the form of pus and make their way     
through the skin to be discharged       
directly4 ,the battle between these     
phagocytes and the bacteria goes on     
vigorously4 ,if in the end the          
phagocytes prove too strong for the     
invaders1 the bacteria are gradually all
 destroyed1 and the attack is repelled4 
,under these circumstances the          
individual commonly knows nothing--of   
the matter4 ,this conflict has taken    
place entirely without any consciousness
 on his part1 and he may not even know  
that he has been exposed to the attack  
of the bacteria4 ,in other cases the    
bacteria prove too strong for the       
phagocytes4 ,they multiply too rapidly1 
and sometimes they produce secretions   
which actually drive the phagocytes     
away4 ,commonly1 as already noticed1 the

 corpuscles are attracted to the point  
of invasion1 but in some cases1 when a  
particularly deadly and vigorous species
 of bacteria invades the body1 the      
secretions produced by them are so      
powerful as actually to drive the       
corpuscles away4 ,under these           
circumstances the invading hosts have a 
chance to multiply unimpeded1 to        
distribute themselves over the body1 and
 the disease rapidly follows as the     
result of their poisoning action on the 
body tissues4  ,it is plain1 then1 that 
the human body is not helpless in the   
presence of the bacteria of disease1 but
 that it is supplied with powerful      
resistant forces4 ,it must not be       
supposed1 however1 that the outline of  
the action of these forces just given is
 anything like a complete account of the
 matter2 nor must it be inferred that   
the resistance is in all respects       
exactly as outlined4 ,the subject has   
only recently been an object of         
investigation1 and we are as yet in the 

dark in regard to many of the facts4    
,the future may require us to modify to 
some extent even the brief outline which
 has been given4 ,but while we recognise
 this uncertainty in the details1 we may
 be assured of the general facts4 ,the  
living body has some very efficacious   
resistant forces which prevent most     
bacteria from growing within its        
tissues1 and which in large measure may 
be relied upon to drive out the true    
pathogenic bacteria4 ,these resistant   
forces are in part associated with the  
productions of body poisons1 and are in 
part associated with the active powers  
of special cells which have been called 
phagocytes4 ,the origin of the poisons  
and the exact method of action of the   
phagocytes we may well leave to the     
future to explain4  ,these resisting    
powers of the body will vary with       
conditions4 ,it is evident that they are
 natural powers1 and they will doubtless
 vary with the general condition of     
vigour of the individual4 ,robust       

health1 a body whose powers are strong1 
well nourished1 and vigorous1 will      
plainly furnish the conditions for the  
greatest resistance to bacterial        
diseases4 ,one whose bodily activities  
are weakened by poor nutrition can offer
 less resistance4 ,the question whether 
one shall suffer from a germ disease is 
not simply the question whether he shall
 be exposed1 or even the question       
whether the bacteria shall find entrance
 into his body4 ,it is equally dependent
 upon whether he has the bodily vigour  
to produce alexines in proper quantity1 
or to summon the phagocytes in          
sufficient abundance and vigour to ward 
off the attack4 ,we may do much to      
prevent disease by sanitation1 which    
aids in protecting the individual from  
attack2 but we must not forget that the 
other half of the battle is of equal    
importance1 and hence we must do all we 
can to strengthen the resisting forces  
of the organism4  ,,recovery ,,from     
,,germ ,,diseases4  ,these resisting    

forces are not always sufficient to     
drive off the invaders4 ,the organisms  
may retain their hold in the body for a 
time and eventually break down the      
resistance4 ,after this they may        
multiply unimpeded and take entire      
possession of the body4 ,as they become 
more numerous their poisonous products  
increase and begin to produce direct    
poisoning effects on the body4 ,the     
incubation period is over and the       
disease comes on4 ,the disease now runs 
its course4 ,it becomes commonly more   
and more severe until a crisis is       
reached4 ,then1 unless the poisoning is 
so severe that death occurs1 the effects
 pass away and recovery takes place4    
,but why should not a germ disease be   
always fatal8 ,if the bacteria thus take
 possession of the body and can grow    
there1 why do they not always continue  
to multiply until they produce          
sufficient poison to destroy the life of
 the individual8 ,such fatal results do1
 of course1 occur1 but in by far the    

larger proportion of cases recovery     
finally takes place4  ,plainly1 the body
 must have another set of resisting     
forces which is concerned in the final  
recovery4 ,although weakened by the     
poisoning and suffering from the        
disease1 it does not yield the battle1  
but somewhat slowly organizes a new     
attack upon the invaders4 ,for a time   
the multiplying bacteria have an        
unimpeded course and grow rapidly2 but  
finally their further increase is       
checked1 their vigour impaired1 and     
after this they diminish in numbers and 
are finally expelled from the body      
entirely4 ,of the nature of this new    
resistance but little is yet known4 ,we 
notice1 in the first place1 that        
commonly after such a recovery the      
individual has decidedly increased      
resistance to the disease4 ,this        
increased resistance may be very        
lasting1 and may be so considerable as  
to give almost complete immunity from   
the disease for many years1 or for life4

 ,one attack of scarlet fever gives the 
individual great immunity for the       
future4 ,on the other hand1 the         
resistance thus derived may be very     
temporary1 as in the case of diphtheria4
 ,but a certain amount of resistance    
appears to be always acquired4 ,this    
power of resisting the activities of the
 parasites seems to be increased during 
the progress of the disease1 and1 if it 
becomes sufficient1 it finally drives   
off the bacteria before they have       
produced death4 ,after this1 recovery   
takes place4 ,to what this newly        
acquired resisting power is due is by no
 means clear to bacteriologists1        
although certain factors are already    
known4 ,it appears beyond question that 
in the case of certain diseases the     
cells of the body after a time produce  
substances which serve as antidotes to  
the poisons produced by the bacteria    
during their growth in the              
body-antitoxines4 ,in the case of       
diphtheria1 for instance1 the germs     

growing in the throat produce poisons   
which are absorbed by the body and give 
rise to the symptoms of the disease2 but
 after a time the body cells react1 and 
themselves produce a counter toxic body 
which neutralizes the poisonous effect  
of the diphtheria poison4 ,this         
substance has been isolated from the    
blood of animals that have recovered    
from an attack of diphtheria1 and has   
been called diphtheria antitoxine4 ,but 
even with this knowledge the recovery is
 not fully explained4 ,this antitoxine  
neutralizes the effects of the          
diphtheria toxine1 and then the body    
develops strength to drive off the      
bacteria which have obtained lodgment in
 the throat4 ,how they accomplish this  
latter achievement we do not know as    
yet4 ,the antitoxme developed simply    
neutralizes the effects of the toxine4  
,some other force must be at work to get
 rid of the bacteria1 a force which can 
only exert itself after the poisoning   
effect of the poison is neutralized4 ,in

 these cases1 then1 the recovery is due1
 first1 to the development in the body  
of the natural antidotes to the toxic   
poisons1 and1 second1 to some other     
unknown force which drives off the      
parasites4  ,these facts are certainly  
surprising4 ,if one had been asked to   
suggest the least likely theory to      
explain recovery from disease1 he could 
hardly have found one more unlikely than
 that the body cells developed during   
the disease an antidote to the poison   
which the disease bacteria were         
producing4 ,nevertheless1 it is beyond  
question that such antidotes are formed 
during the course of the germ diseases4 
,it has not yet been shown in all       
diseases1 and it would be entirely too  
much to claim that this is the method of
 recovery in all cases4 ,we may say1    
however1 in regard to bacterial diseases
 in general1 that after the bacteria    
enter the body at some weak point they  
have first a battle to fight with the   
resisting powers of the body1 which     

appear to be partly biological and      
partly chemical4 ,these resisting powers
 are in many cases entirely sufficient  
to prevent the bacteria from obtaining a
 foothold4 ,if the invading host        
overcome the resisting powers1 then they
 begin to multiply rapidly1 and take    
possession of the body or some part of  
it4 ,they continue to grow until either 
the individual dies or something occurs 
to check their growth4 ,after the       
individual develops the renewed powers  
of checking their growth1 recovery takes
 place1 and the individual is then1     
because of these renewed powers of      
resistance1 immune from a second attack 
of the disease for a variable length of 
time4  ,this1 in the merest outline1    
represents the relation of bacterial    
parasites to the human body ,but while  
this is a fair general expression of the
 matter1 it must be recognised that     
different diseases differ much in their 
relations1 and no general outline will  
apply to all ,they differ in their      

method of attack and in the point of    
attack4 ,not only do they produce       
different kinds of poisons giving rise  
to different symptoms of poisoning2 not 
only do they produce different results  
in different animals2 not only do the   
different pathogenic species differ much
 in their power to develop serious      
disease1 but the different species are  
very particular as to what species of   
animal they attack4 ,some of them can   
live as parasites in man alone2 some can
 live as parasites upon man and the     
mouse and a few other animals2 some can 
live in various animals but not in man2 
some appear to be able to live in the   
field mouse1 but not in the common      
mouse2 some live in the horse2 some in  
birds1 but not in warm-blooded mammals2 
while others1 again1 can live almost    
equally well in the tissues of a long   
list of animals4 ,those which can live  
as parasites upon man are1 of course1   
especially related to human disease1 and
 are of particular interest to the      

physician1 while those which live in    
animals are in a similar way of interest
 to veterinarians4  ,thus we see that   
parasitic bacteria show the widest      
variations4 ,they differ in point of    
attack1 in method of attack1 and in the 
part of the body which they seize upon  
as a nucleus for growth4 ,they differ in
 violence and in the character of the   
poisons they produce1 as well as in     
their power of overcoming the resisting 
powers of the body4 ,they differ at     
different times in their powers of      
producing disease4 ,in short1 they show 
such a large number of different methods
 of action that no general statements   
can be made which will apply            
universally1 and no one method of       
guarding against them or in driving them
 off can be hoped to apply to any       
extended list of diseases4  ,,diseases  
,,caused ,,by ,,other ,,organisms ,,than
 ,,bacteria4  ,although the purpose of  
this work is to deal primarily with the 
bacterial world1 it would hardly be     

fitting to leave the subject without    
some reference to diseases caused by    
organisms which do not belong to the    
group of bacteria4 ,while most of the   
so-called germ diseases are caused by   
the bacteria which we have been studying
 in the previous chapters1 there are    
some whose inciting cause is to be found
 among organisms belonging to other     
groups4 ,some of these are plants of a  
higher organization than bacteria1 but  
others are undoubtedly microscopic      
animals4 ,their life habits are somewhat
 different from those of bacteria1 and  
hence the course of the diseases is     
commonly different4 ,of the diseases    
thus produced by microscopic animals or 
by higher plants1 one or two are of     
importance enough to deserve special    
mention here4  ,malaria4--,the most     
important of these diseases is malaria  
in its various forms1 and known under   
various names--chills and fever1        
autumnal fever1 etc4 ,this disease1 so  
common almost everywhere1 has been      

studied by physicians and scientists for
 a long time1 and many have been the    
causes assigned to it4 ,at one time it  
was thought to be the result of the     
growth of a bacterium1 and a distinct   
bacillus was described as producing it4 
,it has finally been shown1 however1 to 
be caused by a microscopic organism     
belonging to the group of unicellular   
animals1 and somewhat closely related to
 the well-known amoeba4 ,this organism  
is shown in ,fig4 #cd4 ,the whole       
history of the malarial organism is not 
yet known4 ,the following statements    
comprise the most important facts known 
in regard to it1 and its relation to the
 disease in man4  ,undoubtedly the      
malarial germ has some home outside the 
human body1 but it is not yet very      
definitely known what this external home
 is2 nor do we know from what source the
 human parasite is derived4 ,it appears 
probable that water serves in some cases
 as its means of transference to man1   
and air in other cases4 ,from some      

external source it gains access to man  
and finds its way into the blood4 ,here 
it attacks the red blood-corpuscles1    
each malarial organism making its way   
into a single one 7,fig4 #cdj74 ,here it
 now grows1 increasing in size at the   
expense of the substance of the         
corpuscle4 ,as it becomes larger it     
becomes granular1 and soon shows a      
tendency to separate into a number of   
irregular masses4 ,finally it breaks up 
into many minute bodies called spores4  
,these bodies break out of the corpuscle
 and for a time live a free life in the 
blood4 ,after a time they make their way
 into other red blood-corpuscles1       
develop into new malarial amoeboid      
parasites1 and repeat the growth and    
sporulation4 ,this process can          
apparently be repeated many times       
without check4  ,these organisms are    
thus to be regarded as parasites of the 
red corpuscles4 ,it is1 of course1 easy 
to believe that an extensive parasitism 
and destruction of the corpuscles would 

be disastrous to the health of the      
individual1 and the severity of the     
disease will depend upon the extent of  
the parasitism4 ,corresponding to this  
life history of the organism1 the       
disease malaria is commonly             
characterized by a decided              
intermittency1 periods of chill and     
fever alternating with periods of       
intermission in which these symptoms are
 abated4 ,the paroxysms of the disease1 
characterized by the chill1 occur at the
 time that the spores are escaping from 
the blood-corpuscles and floating in the
 blood4 ,after they have again found    
their way into a blood-corpuscle the    
fever diminishes1 and during their      
growth in the corpuscle until the next  
sporulation the individual has a rest   
from the more severe symptoms4  ,there  
appears to be more than one variety of  
the malarial organism1 the different    
types differing in the length of time it
 takes for their growth and sporulation4
 ,there is one variety1 the most common 

one1 which requires two days for its    
growth1 thus giving rise to the paroxysm
 of the disease about once in forty-    
eight hours2 another variety appears to 
require three days for its growth2 while
 still another variety appears to be    
decidedly irregular in its period of    
growth and sporulation4 ,these facts    
readily explain some of the variations  
in the disease4 ,certain other          
irregularities appear to be due to a    
different cause4 ,more than one brood of
 parasites may be in the blood of the   
individual at the same time1 one        
producing sporulation at one time and   
another at a different time4 ,such a    
simultaneous growth of two independent  
broods may plainly produce almost any   
kind of modification in the regularity  
of the disease4  ,the malarial organism 
appears to be very sensitive to quinine1
 a very small quantity being sufficient 
to kill it4 ,upon this point depends the
 value of quinine as a medicine4 ,if the
 drug be present in the blood at the    

time when the spores are set free from  
the blood-corpuscle1 they are rapidly   
killed by it before they have a chance  
to enter another corpuscle4 ,during     
their growth in the corpuscle they are  
far less sensitive to quinine than when 
they exist in the free condition as     
spores1 and at this time the drug has   
little effect4  ,the malarial organism  
is an animal1 and can not be cultivated 
in the laboratory by any artificial     
method yet devised4 ,its whole history  
is therefore not known4 ,it doubtless   
has some home outside the blood of      
animals1 and very likely it may pass    
through other stages of a metamorphosis 
in the bodies of other animals4 ,most   
parasitic animals have two or more hosts
 upon which they live1 alternating from 
one to the other1 and that such is the  
case with the malarial parasite is at   
least probable4 ,but as yet             
bacteriologists have been unable to     
discover anything very definite in      
regard to the matter4 ,until we can     

learn something in regard to its life   
outside the blood of man we can do      
little in the way of devising methods to
 avoid it4  ,malaria differs from most  
germ diseases in the fact that the      
organisms which produce it are not      
eliminated from the body in any way4 ,in
 most germ diseases the germs are       
discharged from the patient by          
secretions or excretions of some kind1  
and from these excretions may readily   
find their way into other individuals4  
,the malarial organism is not discharged
 from the body in any way1 and hence is 
not contagious4 ,if the parasite does   
pass part of its history in some other  
animal than man1 there must be some     
means by which it passes from man to its
 other host4 ,it has been suggested that
 some of the insects which feed upon    
human blood may serve as the second host
 and become inoculated when feeding upon
 such blood4 ,this has been demonstrated
 with startling success in regard to the
 mosquito 7,anopheles71 some            

investigators going so far as to say    
that this is the only way in which the  
disease can be communicated4  ,several  
other microscopic animals occur as      
parasites upon man1 and some of them are
 so definitely associated with certain  
diseases as to lead to the belief that  
they are the cause of these diseases4   
,the only one of very common occurrence 
is a species known as ,amaeba coli1     
which is found in cases of dysentery4   
,in a certain type of dysentery this    
organism is so universally found that   
there is little doubt that it is in some
 very intimate way associated with the  
cause of the disease4 ,definite proof of
 the matter is1 however1 as yet wanting4
  ,on the side of plants1 we find that  
several plants of a higher organization 
than bacteria may become parasitic upon 
the body of man and produce various     
types of disease4 ,these plants belong  
mostly to the same group as the moulds1 
and they are especially apt to attack   
the skin4 ,they grow in the skin1       

particularly under the hair1 and may    
send their threadlike branches into some
 of the subdermal tissues4 ,this        
produces irritation and inflammation of 
the skin1 resulting in trouble1 and     
making sores difficult to heal4 ,so long
 as the plant continues to grow1 the    
sores1 of course1 can not be healed1 and
 when the organisms get into the skin   
under the hair it is frequently         
difficult to destroy them4 ,among the   
diseases thus caused are ringworm1      
thrush1 alopecia1 etc4      ,,chapter   
,,vi4  ,,methods ,,of ,,combating       
,,parasitic ,,bacteria4   ,the chief    
advantage of knowing the cause of       
disease is that it gives us a vantage   
ground from which we may hope to find   
means of avoiding its evils4 ,the study 
of medicine in the past history of the  
world has been almost purely empirical1 
with a very little of scientific basis4 
,great hopes are now entertained that   
these new facts will place this matter  
upon a more strictly scientific         

foundation4 ,certainly in the past      
twenty-five years1 since bacteriology   
has been studied1 more has been done to 
solve problems connected with disease   
than ever before4 ,this new knowledge   
has been particularly directed toward   
means of avoiding disease4 ,bacteriology
 has thus far borne fruit largely in the
 line of preventive medicine1 although  
to a certain extent also along the line 
of curative medicine4 ,this chapter will
 be devoted to considering how the study
 of bacteriology has contributed        
directly and indirectly to our power of 
combating disease4  ,,preventive        
,,medicine4  ,in the study of medicine  
in the past centuries the only aim has  
been to discover methods of curing      
disease2 at the present time a large and
 increasing amount of study is devoted  
to the methods of preventing disease4   
,preventive medicine is a development of
 the last few years1 and is based almost
 wholly upon our knowledge of bacteria4 
,this subject is yearly becoming of more

 importance4 ,forewarned is forearmed1  
and it has been found that to know the  
cause of a disease is a long step toward
 avoiding it4 ,as some of our contagious
 and epidemic diseases have been studied
 in the light of bacteriological        
knowledge1 it has been found possible to
 determine not only their cause1 but    
also how infection is brought about1 and
 consequently how contagion may be      
avoided4 ,some of the results which have
 grown up so slowly as to be hardly     
appreciated are really great triumphs4  
,for instance1 the study of bacteriology
 first led us to suspect1 and then      
demonstrated1 that tuberculosis is a    
contagious disease1 and from the time   
that this was thus proved there has been
 a slow1 but1 it is hoped1 a sure       
decline in this disease4                
,bacteriological study has shown that   
the source of cholera infection in cases
 of raging epidemics is1 in large part  
at least1 our drinking water2 and since 
this has been known1 although cholera   

has twice invaded ,europe1 and has been 
widely distributed1 it has not obtained 
any strong foothold or given rise to any
 serious epidemic except in a few cases 
where its ravages can be traced to      
recognised carelessness4 ,it is very    
significant to compare the history of   
the cholera epidemics of the past few   
years with those of earlier dates4 ,in  
the epidemics of earlier years the      
cholera swept ruthlessly through        
communities without check4 ,in the last 
few years1 although it has repeatedly   
knocked at the doors of many ,european  
cities1 it has been commonly confined to
 isolated cases1 except in a few        
instances where these facts concerning  
the relation to drinking water were     
ignored4  ,the study of preventive      
medicine is yet in its infancy1 but it  
has already accomplished much4 ,it has  
developed modern systems of sanitation1 
has guided us in the building of        
hospitals1 given rules for the          
management of the sick-room which       

largely prevent contagion from patient  
to nurse2 it has told us what diseases  
are contagious1 and in what way2 it has 
told us what sources of contagion should
 be suspected and guarded against1 and  
has thus done very much to prevent the  
spread of disease4 ,its value is seen in
 the fact that there has been a constant
 decrease in the death rate since modern
 ideas of sanitation began to have any  
influence1 and in the fact that our     
general epidemics are less severe than  
in former years1 as well as in the fact 
that more people escape the diseases    
which were in former times almost       
universal4  ,the study of preventive    
medicine takes into view several        
factors1 all connected with the method  
and means of contagion4 ,they are the   
following3  ,the ,source of ,infectious 
,material4--t has been learned that for 
most diseases the infectious material   
comes from individuals suffering with   
the disease1 and that except in a few   
cases1 like malaria1 we must always look

 to individuals suffering from disease  
for all sources of contagion4 ,it is    
found that pathogenic bacteria are in   
all these cases eliminated from the     
patient in some way1 either from the    
alimentary canal or from skin secretions
 or otherwise1 and that any nurse with  
common sense can have no difficulty in  
determining in what way the infectious  
material is eliminated from her         
patients4 ,when this fact is known and  
taken into consideration it is a        
comparatively easy matter to devise     
valuable precautions against            
distribution of such material4 ,it is   
thus of no small importance to remember 
that the simple presence of bacteria in 
food or drink is of no significance     
unless these bacteria have come from    
some source of disease infection4  ,the 
,method of ,distribution4--,the bacteria
 must next get from the original source 
of the disease to the new susceptible   
individual4 ,bacteria have no           
independent powers of distribution      

unless they be immersed in liquids1 and 
therefore their passage from individual 
to individual must be a passive one4    
,they are readily transferred1 however1 
by a number of different means1 and the 
study of these means is aiding much in  
checking contagion ,study along this    
line has shown that the means by which  
bacteria are carried are several4 ,first
 we may notice food as a distributor4   
,food may become contaminated by        
infectious material in many ways2 for   
example1 by contact with sewage1 or with
 polluted water1 or even with eating    
utensils which have been used by        
patients4 ,water is also likely to be   
contaminated with infectious material1  
and is a fertile source for distributing
 typhoid and cholera4 ,milk may become  
contaminated in a variety of ways1 and  
be a source of distributing the bacteria
 which produce typhoid fever1           
tuberculosis1 diphtheria1 scarlet fever1
 and a few other less common diseases4  
,again1 infected clothing1 bedding1 or  

eating utensils may be taken from a     
patient and be used by another          
individual without proper cleansing4    
,direct contact1 or contact with        
infected animals1 furnishes another     
method4 ,insects sometimes carry the    
bacteria from person to person1 and in  
some diseases 7tuberculosis1 and perhaps
 scarlet fever and smallpox7 we must    
look to the air as a distributor of the 
infectious material4 ,knowledge of these
 facts is helping to account for        
multitudes of mysterious cases of       
infection1 especially when we combine   
them with the known sources of          
contagious matter4  ,means of           
,invasion4--,bacteriology has shown us  
that different species of parasitic     
bacteria have different means of        
entering the body1 and that each must   
enter the proper place in order to get a
 foothold4 ,after we learn that typhoid 
infectious material must enter the mouth
 in order to produce the disease2 that  
tuberculosis may find entrance through  

the nose in breathing1 while types of   
blood poisoning enter only through      
wounds or broken skin1 we learn at once 
fundamental facts as to the proper      
methods of meeting these dangers4 ,we   
learn that with some diseases care      
exercised to prevent the swallowing of  
infectious material is sufficient to    
prevent contagion1 while with others    
this is entirely insufficient4 ,when all
 these facts are understood it is almost
 always perfectly possible to avoid     
contagion2 and as these facts become    
more and more widely known direct       
contagion is sure to become less        
frequent4  ,above all1 it is telling us 
what becomes of the pathogenic bacteria 
after being eliminated from the body of 
the patient2 how they may exist for a   
long time still active2 how they may    
lurk in filth or water dormant but      
alive1 or how they may even multiply    
there4 ,preventive medicine is telling  
us how to destroy those thus lying in   
wait for a chance of infection1 by      

discovering disinfectants and telling us
 especially where and when to use them4 
,it has already taught us how to crush  
out certain forms of epidemics by the   
proper means of destroying bacteria1 and
 is lessening the dangers from          
contagious diseases4 ,in short1 the     
study of bacteriology has brought us    
into a condition where we are no longer 
helpless in the presence of a raging    
epidemic4 ,we no longer sit in helpless 
dismay1 as did our ancestors1 when an   
epidemic enters a community1 but1       
knowing their causes and sources1 set   
about at once to remove them4 ,as a     
result1 severe epidemics are becoming   
comparatively short-lived4  ,,bacteria  
,,in ,,surgery4  ,in no line of         
preventive medicine has bacteriology    
been of so much value and so striking in
 its results as in surgery4 ,ever since 
surgery has been practised surgeons have
 had two difficulties to contend with4  
,the first has been the shock resulting 
from the operation4 ,this is dependent  

upon the extent of the operation1 and   
must always be a part of a surgical     
operation4 ,the second has been         
secondary effects following the         
operation4 ,after the operation1 even   
though it was successful1 there were    
almost sure to arise secondary          
complications known as surgical fever1  
inflammation1 blood poisoning1 gangrene1
 etc41 which frequently resulted        
fatally4 ,these secondary complications 
were commonly much more serious than the
 shock of the operation1 and it used to 
be the common occurrence for the patient
 to recover entirely from the shock1 but
 yield to the fevers which followed4    
,they appeared to be entirely           
unavoidable1 and were indeed regarded as
 necessary parts of the healing of the  
wound4 ,too frequently it appeared that 
the greater the care taken with the     
patient the more likely he was to suffer
 from some of these troubles4 ,the      
soldier who was treated on the          
battlefield and nursed in an improvised 

field hospital would frequently recover1
 while the soldier who had the fortune  
to be taken into the regular hospital1  
where greater care was possible1        
succumbed to hospital gangrene4 ,all    
these facts were clearly recognised1 but
 the surgeon1 through ignorance of their
 cause1 was helpless in the presence of 
these inflammatory troubles1 and felt it
 always necessary to take them into     
consideration4  ,the demonstration that 
putrefaction and decay were caused by   
bacteria1 and the early proof that the  
silkworm disease was produced by a      
micro-organism1 led to the suggestion   
that the inflammatory diseases          
accompanying wounds were similarly      
caused4 ,there are many striking        
similarities between these troubles and 
putrefaction1 and the suggestion was an 
obvious one4 ,at first1 however1 and for
 quite a number of years1 it was        
impossible to demonstrate the theory by 
finding the distinct species of micro-  
organisms which produced the troubles4  

,we have already seen that there are    
several different species of bacteria   
which are associated with this general  
class of diseases1 but that no specific 
one has any particular relation to a    
definite type of inflammation4 ,this    
fact made discoveries in this connection
 a slow matter from the microscopical   
standpoint4 ,but long before this       
demonstration was finally reached the   
theory had received practical           
application in the form of what has     
developed into antiseptic or aseptic    
surgery4  ,antiseptic surgery is based  
simply upon the attempt to prevent the  
entrance of bacteria into the surgical  
wound4 ,it is assumed that if these     
organisms are kept from the wound the   
healing will take place without the     
secondary fevers and inflammations which
 occur if they do get a chance to grow  
in the wound4 ,the theory met with      
decided opposition at first1 but        
accumulating facts demonstrated its     
value1 and to-day its methods have been 

adopted everywhere in the civilized     
world4 ,as the evidence has been        
accumulating1 surgeons have learned many
 important facts1 foremost among which  
is a knowledge of the common sources    
from which the infection of wounds      
occurs4 ,at first it was thought that   
the air was the great source of         
infection1 but the air bacteria have    
been found to be usually harmless4 ,it  
has appeared that the more common       
sources are the surgeon's instruments1  
or his hands1 or the clothing or sponges
 which are allowed to come in contact   
with the wounds4 ,it has also appeared  
that the bacteria which produce this    
class of troubles are common species1   
existing everywhere and universally     
present around the body1 clinging to the
 clothing or skin1 and always on hand to
 enter the wound if occasion offers4    
,they are always present1 but commonly  
harmless4 ,they are not foreign invaders
 like the more violent pathogenic       
species1 such as those of ,asiatic      

cholera1 but may be compared to domestic
 enemies at hand4 ,it is these          
ever-present bacteria which the surgeon 
must guard against4 ,the methods by     
which he does this need not detain us   
here4 ,they consist essentially in      
bacteriological cleanliness4 ,the       
operation is performed with sterilized  
instruments under most exacting         
conditions of cleanliness4  ,the result 
has been a complete revolution in       
surgery4 ,as the methods have become    
better understood and more thoroughly   
adopted1 the instances of secondary     
troubles following surgical wounds have 
become less and less frequent until they
 have practically disappeared in all    
simple cases4 ,to-day the surgeon       
recognises that when inflammatory       
troubles of this sort follow simple     
surgical wounds it is a testimony to his
 carelessness4 ,the skilful surgeon has 
learned that with the precautions which 
he is able to take to-day he has to fear
 only the direct effect of the shock of 

the wound and its subsequent direct     
influence2 but secondary surgical       
fevers1 blood poisoning1 and surgical   
gangrene need not be taken into         
consideration at all4 ,indeed1 the      
modern surgeon hardly knows what        
surgical gangrene is1 and               
bacteriologists have had practically no 
chance to study it4 ,secondary          
infections have largely disappeared1 and
 the surgeon is concerned simply with   
the effect of the wound itself1 and the 
power of the body to withstand the shock
 and subsequently heal the wound4  ,with
 these secondary troubles no longer to  
disturb him1 the surgeon has become more
 and more bold4 ,operations formerly not
 dreamed of are now performed without   
hesitation4 ,in former years an         
operation which opened the abdominal    
cavity was not thought possible1 or at  
least it was so nearly certain to result
 fatally that it was resorted to only on
 the last extremity2 while to-day such  
operations are hardly regarded as       

serious4 ,even brain surgery is becoming
 more and more common4 ,possibly our    
surgeons are passing too far to the     
other extreme1 and1 feeling their power 
of performing so many operations without
 inconvenience or danger1 they are using
 the knife in cases where it would be   
better to leave ,nature to herself for  
her own healing4 ,but1 be this as it    
may1 it is impossible to estimate the   
amount of suffering prevented and the   
number of lives saved by the mastery of 
the secondary inflammatory troubles     
which used to follow surgical wounds4   
,preventive medicine1 then1 has for its 
object the prevention rather than the   
cure of disease4 ,by showing the causes 
of disease and telling us where and how 
they are contracted1 it is telling us   
how they may to a large extent be       
avoided4 ,unlike practical medicine1    
this subject is one which has a direct  
relation to the general public4 ,while  
it may be best that the knowledge of    
curative methods be confined largely to 

the medical profession1 it is eminently 
desirable that a knowledge of all the   
facts bearing upon preventive medicine  
should be distributed as widely as      
possible4 ,one person can not           
satisfactorily apply his knowledge of   
preventive medicine1 if his neighbour is
 ignorant of or careless of the facts4  
,we can not hope to achieve the         
possibilities lying along this line     
until there is a very wide distribution 
of knowledge4 ,every epidemic that      
sweeps through our communities is a     
testimony to the crying need of         
education in regard to such simple facts
 as the source of infectious material1  
the methods of its distribution1 and the
 means of rendering it harmless4        
,,prevention ,,in ,,inoculation4  ,it   
has long been recognised that in most   
cases recovery from one attack of a     
contagious disease renders an individual
 more or less immune against a second   
attack4 ,it is unusual for an individual
 to have the same contagious disease    

twice4 ,this belief is certainly based  
upon fact1 although the immunity thus   
acquired is subject to wide variations4 
,there are some diseases in which there 
is little reason for thinking that any  
immunity is acquired1 as in the case of 
tuberculosis1 while there are others in 
which the immunity is very great and    
very lasting1 as in the case of scarlet 
fever4 ,moreover1 the immunity differs  
with individuals4 ,while some persons   
appear to acquire a lasting immunity by 
recovery from a single attack1 others   
will yield to a second attack very      
readily4 ,but in spite of this the fact 
of such acquired immunity is beyond     
question4 ,apparently all infectious    
diseases from which a real recovery     
takes place are followed by a certain   
amount of protection from a second      
attack2 but with some diseases the      
immunity is very fleeting1 while with   
others it is more lasting4 ,diseases    
which produce a general infection of the
 whole system are1 as a rule1 more      

likely to give rise to a lasting        
immunity than those which affect only   
small parts4 ,tuberculosis1 which1 as   
already noticed1 is commonly quite      
localized in the body1 has little power 
of conveying immunity1 while a disease  
like scarlet fever1 which affects the   
whole system1 conveys a more lasting    
protection4  ,such immunity has long    
been known1 and in the earlier years was
 sometimes voluntarily acquired2 even   
to-day we find some individuals making  
use of the principle4 ,it appears that a
 mild attack of such diseases produces  
immunity equally well with a severe     
attack1 and acting upon this fact       
mothers have not infrequently           
intentionally exposed their children to 
certain diseases at seasons when they   
are mild1 in order to have the disease  
over with and their children protected  
in the future4 ,even the more severe    
diseases have at times been thus        
voluntarily acquired4 ,in ,china it has 
sometimes been the custom thus to       

acquire smallpox4 ,such methods are     
decidedly heroic1 and of course to be   
heartily condemned4 ,but the principle  
that a mild type of the disease conveys 
protection has been made use of in a    
more logical and defensible way4  ,the  
first instance of this principle was in 
vaccination against smallpox1 now       
practised for more than a century4      
,cowpox is doubtless closely related to 
smallpox1 and an attack of the former   
conveys a certain amount of protection  
against the latter4 ,it was easy1       
therefore1 to inoculate man with some of
 the infectious material from cowpox1   
and thus give him some protection       
against the more serious smallpox4 ,this
 was a purely empirical discovery1 and  
vaccination was practised long before   
the principle underlying it was         
understood1 and long before the germ    
nature of disease was recognised4 ,the  
principle was revived again1 however1 by
 ,pasteur1 and this time with a logical 
thought as to its value4 ,while working 

upon anthrax among animals1 he learned  
that here1 as in other diseases1        
recovery1 when it occurred1 conveyed    
immunity4 ,this led him to ask if it    
were not possible to devise a method of 
giving to animals a mild form of the    
disease and thus protect them from the  
more severe type4 ,the problem of giving
 a mild type of this extraordinarily    
severe disease was not an easy one4 ,it 
could not be done1 of course1 by        
inoculating the animals with a small    
number of the bacteria1 for their power 
of multiplication would soon make them  
indefinitely numerous4 ,it was necessary
 in some way to diminish their violence4
 ,pasteur succeeded in doing this by    
causing them to grow in culture fluids  
for a time at a high temperature4 ,this 
treatment diminished their violence so  
much that they could be inoculated into 
cattle1 where they produced only the    
mildest type of indisposition1 from     
which the animals speedily recovered4   
,but even this mild type of the disease 

was triumphantly demonstrated to protect
 the animals from the most severe form  
of anthrax4 ,the discovery was naturally
 hailed as a most remarkable one1 and   
one which promised great things in the  
future4 ,if it was thus possible1 by    
direct laboratory methods1 to find a    
means of inoculating against a serious  
disease like anthrax1 why could not the 
same principle be applied to human      
diseases8 ,the enthusiasts began at once
 to look forward to a time when all     
diseases should be thus conquered4  ,but
 the principle has not borne the fruit  
at first expected4 ,there is little     
doubt that it might be applied to quite 
a number of human diseases if a serious 
attempt should be made4 ,but several    
objections arise against its wide       
application4 ,in the first place1 the   
inoculation thus necessary is really a  
serious matter4 ,even vaccination1 as is
 well known1 sometimes1 through faulty  
methods1 results fatally1 and it is a   
very serious thing to experiment upon   

human beings with anything so powerful  
for ill as pathogenic bacteria4 ,the    
seriousness of the disease smallpox1 its
 extraordinary contagiousness1 and the  
comparatively mild results of           
vaccination1 have made us willing to    
undergo vaccination at times of         
epidemics to avoid the somewhat great   
probability of taking the disease4 ,but 
mankind is unwilling to undergo such an 
operation1 even though mild1 for the    
purpose of avoiding other less severe   
diseases1 or diseases which are less    
likely to be taken4 ,we are unwilling to
 be inoculated against mild diseases1 or
 against the more severe ones which are 
uncommon4 ,for instance1 a method has   
been devised for rendering animals      
immune against lockjaw1 which would     
probably apply equally well to man4 ,but
 mankind in general will never adopt it1
 since the danger from lockjaw is so    
small4 ,inoculation must then be        
reserved for diseases which are so      
severe and so common1 or which occur in 

periodical epidemics of so great        
severity1 as to make people in general  
willing to submit to inoculation as a   
protection4 ,a further objection arises 
from the fact that the immunity acquired
 is not necessarily lasting4 ,the cattle
 inoculated against anthrax retain their
 protective powers for only a few       
months4 ,how long similar immunity might
 be retained in other cases we can not  
say1 but plainly this fact would        
effectually prevent this method of      
protecting mankind from being used      
except in special cases4 ,it is out of  
the question to think of constant and   
repeated inoculations against various   
diseases4  ,as a result1 the principle  
of inoculation as an aid in preventive  
medicine has not proved of very much    
value4 ,the only other human disease in 
which it has been attempted seriously is
 ,asiatic cholera4 ,this disease in     
times of epidemics is so severe and the 
chance of infection is so great as to   
justify such inoculation4 ,several      

bacteriologists have in the last few    
years been trying to discover a harmless
 method of inoculating against this     
disease4 ,apparently they have          
succeeded1 for experiments in ,india1   
the home of the cholera1 have been as   
successful as could be anticipated4     
,bacteriological science has now in its 
possession a means of inoculation       
against cholera which is perhaps as     
efficacious as vaccination is against   
smallpox4 ,whether it will ever be used 
to any extent is doubtful1 since1 as    
already pointed out1 we are in a        
position to avoid cholera epidemics by  
other means4 ,if we can protect our     
communities by guarding the water       
supply1 it is not likely that the method
 of inoculation will ever be widely     
used4  ,another instance of the         
application of preventive inoculation   
has been made1 but one based upon a     
different principle4 ,hydrophobia is    
certainly one of the most horrible of   
diseases1 although comparatively rare4  

,its rarity would effectually prevent   
mankind from submitting to a general    
inoculation against it1 but its severity
 would make one who had been exposed to 
it by the bite of a rabid animal ready  
to submit to almost any treatment that  
promised to ward off the disease4 ,in   
the attempt to discover a means of      
inoculating against this disease it was 
necessary1 therefore1 to find a method  
that could be applied after the time of 
exposure--i4e41 after the individual had
 been bitten by the rabid animal4       
,fortunately1 the disease has a long    
period of incubation1 and one that has  
proved long enough for the purpose4 ,a  
method of inoculation against this      
disease has been devised by ,pasteur1   
which can be applied after the          
individual has been bitten by the rabid 
animal4 ,apparently1 however1 this      
preventive inoculation is dependent upon
 a different principle from vaccination 
or inoculation against anthrax4 ,it does
 not appear to give rise to a mild form 

of the disease1 thus protecting the     
individual1 but rather to an acquired   
tolerance of the chemical poisons       
produced by the disease4 ,it is a       
well-known physiological fact that the  
body can become accustomed to tolerate  
poisons if inured to them by            
successively larger and larger doses4   
,it is by this power1 apparently1 that  
the inoculation against hydrophobia     
produces its effect4 ,material          
containing the hydrophobia poison 7taken
 from the spinal cord of a rabbit dead  
with the disease7 is injected into the  
individual after he has been bitten by a
 rabid animal4 ,the poisonous material  
in the first injection is very weak1 but
 is followed later by a more powerful   
inoculation4 ,the result is that after a
 short time the individual has acquired 
the power of resisting the hydrophobia  
poisons4 ,before the incubation period  
of the original infectious matter from  
the bite of the rabid animal has passed1
 the inoculated individual has so       

thoroughly acquired a tolerance of the  
poison that he successfully resists the 
attack of the infection4 ,this method of
 inoculation thus neutralizes the       
effects of the disease by anticipating  
them4  ,the method of treatment of      
hydrophobia met with extraordinarily    
violent opposition4 ,for several years  
it was regarded as a mistake4 ,but the  
constantly accumulating statistics from 
the ,pasteur ,institute have been so    
overwhelmingly on one side as to quiet  
opposition and bring about a general    
conviction that the method is a success4
  ,the method of preventive inoculation 
has not been extensively applied to     
human diseases in addition to those     
mentioned4 ,in a few cases a similar    
method has been used to guard against   
diphtheria4 ,among animals1 experiment  
has shown that such methods can quite   
easily be obtained1 and doubtless the   
same would be true of mankind if it was 
thought practical or feasible to apply  
them4 ,but1 for reasons mentioned1 this 

feature of preventive medicine will     
always remain rather unimportant1 and   
will be confined to a few of the more   
violent diseases4  ,it may be well to   
raise the question as to why a single   
attack with recovery conveys immunity4  
,this question is really a part of the  
one already discussed as to the method  
by which the body cures disease4 ,we    
have seen that this is in part due to   
the development of chemical substances  
which either neutralize the poisons or  
act as germicide upon the bacteria1 or  
both1 and perhaps due in part to an     
active destruction of bacteria by       
cellular activity 7phagocytosis74 ,there
 is little reason to doubt that it is   
the same set of activities which renders
 the animal immune4 ,the forces which   
drive off the invading bacteria in one  
case are still present to prevent a     
second attack of the same species of    
bacterium4 ,the length of time during   
which these forces are active and       
sufficient to cope with any new invaders

 determines the length of time during   
which the immunity lasts4 ,until1       
therefore1 we can answer with more      
exactness just how cure is brought about
 in case of disease1 we shall be unable 
to explain the method of immunity4      
,,limits ,,of ,,preventive ,,medicine4  
,with all the advance in preventive     
medicine we can not hope to avoid       
disease entirely4 ,we are discovering   
that the sources of disease are on all  
sides of us1 and so omnipresent that to 
avoid them completely is impossible4 ,if
 we were to apply to our lives all the  
safeguards which bacteriology has taught
 us should be applied in order to avoid 
the different diseases1 we would        
surround ourselves with conditions which
 would make life intolerable4 ,it would 
be oppressive enough for us to eat no   
food except when it is hot1 to drink no 
water except when boiled1 and to drink  
no milk except after sterilization2 but 
these would not satisfy the necessary   
conditions for avoiding disease4 ,to    

meet all dangers1 we should handle      
nothing which has not been sterilized1  
or should follow the handling by        
immediately sterilizing the hands2 we   
should wear only disinfected clothes1 we
 should never put our fingers in our    
mouths or touch our food with them2 we  
should cease to ride in public          
conveyances1 and1 indeed1 should cease  
to breathe common air4 ,absolute        
prevention of the chance of infection is
 impossible4 ,the most that preventive  
medicine can hope for is to point out   
the most common and prolific sources of 
infection1 and thus enable civilized man
 to avoid some of his most common       
troubles4 ,it becomes a question1       
therefore1 where we will best draw the  
line in the employment of safeguards4   
,shall we drink none except sterilized  
milk1 and no water unless boiled8 or    
shall we put these occasional sources of
 danger in the same category with       
bicycle and railroad accidents1 dangers 
which can be avoided by not using the   

bicycle or riding on the rail1 but in   
regard to which the remedy is too       
oppressive for application8  ,indeed1   
when viewed in a broad philosophical    
light it may not be the best course for 
mankind to shun all dangers4 ,strength  
in the organism comes from the use      
rather than the disuse of our powers4   
,it is certain that the general health  
and vigour of mankind is to be developed
 by meeting rather than by shunning     
dangers4 ,resistance to disease means   
bodily vigour1 and this is to be        
developed in mankind by the application 
of the principle of natural selection4  
,in accordance with this principle1     
disease will gradually remove the       
individuals of weak resisting powers1   
leaving those of greater vigour4        
,parasitic bacteria are thus a means of 
preventing the continued life of the    
weaker members of the community1 and so 
tend to strengthen mankind4 ,by         
preventive medicine many a weak         
individual who would otherwise succumb  

earlier in the struggle is enabled to   
live a few years longer4 ,whatever be   
our humanitarian feeling for the        
individual1 we can not fail to admit    
that this survival of the weak is of no 
benefit to the race so far as the       
development of physical nature is       
concerned4 ,indeed1 if we were to take  
into consideration simply the physical  
nature of man we should be obliged to   
recommend a system such as the ancient  
,spartans developed1 of exposing to     
death all weakly individuals1 that only 
the strong might live to become the     
fathers of future generations4 ,in this 
light1 of course1 parasitic diseases    
would be an assistance rather than a    
detriment to the human race4 ,of course 
such principles will never again be     
dominant among men1 and our conscience  
tells us to do all we can to help the   
weak4 ,we shall doubtless do all        
possible to develop preventive medicine 
in order to guard the weak against      
parasitic organisms4 ,but it is at all  

events well for us to remember that we  
can never hope to develop the strength  
of the human race by shunning evil1 but 
rather by combating it1 and the power of
 the human race to resist the invasions 
of these organisms will never be        
developed by the line of action which   
guards us from attack4 ,here1 as in     
other directions1 the principles of     
modern humanity have1 together with     
their undoubted favourable influence    
upon mankind1 certain tendencies toward 
weakness4 ,while we shall still do our  
utmost to develop preventive medicine in
 a proper way1 it may be well for us to 
remember these facts when we come to the
 practical question of determining where
 to draw the limits of the application  
of methods for preventing infectious    
diseases4  ,,curative ,,medicine4       
,bacteriology has hitherto contributed  
less to curative than to preventive     
medicine4 ,nevertheless1 its            
contributions to curative medicine have 
not been unimportant1 and there is      

promise of much more in the future4 ,it 
is1 of course1 unsafe to make           
predictions for the future1 but the     
accomplishments of the last few years   
give much hope as to further results4   
,,drugs4  ,it was at first thought that 
a knowledge of the specific bacteria    
which cause a disease would give a ready
 means of finding specific drugs for the
 cure of such disease4 ,if a definite   
species of bacterium causes a disease   
and we can cultivate the organism in the
 laboratory1 it is easy to find some    
drugs which will be fatal to its growth1
 and these same drugs1 it would seem1   
should be valuable as medicines in these
 diseases4 ,this hope has1 however1     
proved largely illusive4 ,it is very    
easy to find some drug which proves     
fatal to the specific germs while       
growing in the culture media of the     
laboratory1 but commonly these are of   
little or no use when applied as        
medicines4 ,in the first place1 such    
substances are usually very deadly      

poisons4 ,corrosive sublimate is a      
substance which destroys all pathogenic 
germs with great rapidity1 but it is a  
deadly poison1 and can not be used as a 
drug in sufficient quantity to destroy  
the parasitic bacteria in the body      
without at the same time producing      
poisonous effects on the body itself4   
,it is evident that for any drug to be  
of value in thus destroying bacteria it 
must have some specially strong action  
upon the bacteria4 ,its germicide action
 on the bacteria should be so strong    
that a dose which would be fatal or very
 injurious to them would be too small to
 have a deleterious influence on the    
body of the individual4 ,it has not     
proved an easy task to discover drugs   
which will have any value as germicides 
when used in quantities so small as to  
produce no injurious effect on the body4
  ,a second difficulty is in getting the
 drug to produce its effect at the right
 point4 ,a few diseases1 as we have     
noticed1 are produced by bacteria which 

distribute themselves almost            
indiscriminately over the body2 but the 
majority are somewhat definitely        
localized in special points4            
,tuberculosis may attack a single gland 
or a single lobe of the lung4 ,typhoid  
germ is localized in the intestines1    
liver1 spleen1 etc4 ,even if it were    
possible to find some drug which would  
have a very specific effect upon the    
tuberculosis bacillus1 it is plain that 
it would be a very questionable method  
of procedure to introduce this into the 
whole system simply that it might have  
an effect upon a very small isolated    
gland4 ,sometimes such a bacterial      
affection may be localized in places    
where it can be specially treated1 as in
 the case of an attack on a dermal      
gland1 and in these cases some of the   
germicides have proved to be of much    
value4 ,indeed1 the use of various      
disinfectants connected with abscesses  
and superficial infections has proved of
 much value4 ,to this extent1 in        

disinfecting wounds and as a local      
application1 the development of our     
knowledge of disinfectants has given no 
little aid to curative medicine4  ,very 
little success1 however1 has resulted in
 the attempt to find specific drugs for 
specific diseases1 and it is at least   
doubtful whether many such will ever be 
found4 ,the nearest approach to it is   
quinine as a specific poison for        
malarial troubles4 ,malarious diseases  
are not1 however1 produced by bacteria  
but by a microscopic organism of a very 
different nature1 thought to be an      
animal rather than a plant4 ,besides    
this there has been little or no success
 in discovering specifics in the form of
 drugs which can be given as medicines  
or inoculated with the hope of          
destroying special kinds of pathogenic  
bacteria without injury to the body4    
,while it is unwise to make predictions 
as to future discoveries1 there seems at
 present little hope for a development  
of curative medicine along these lines4 

,,vis ,,medicatrix ,,naturae4  ,the     
study of bacterial diseases as they     
progress in the body has emphasized     
above all things the fact that diseases 
are eventually cured by a natural rather
 than by an artificial process4 ,if a   
pathogenic bacterium succeeds in passing
 the outer safeguards and entering the  
body1 and if it then succeeds in        
overcoming the forces of resistance     
which we have already noticed1 it will  
begin to multiply and produce mischief4 
,this multiplication now goes on for a  
time unchecked1 and there is little     
reason to expect that we can ever do    
much toward checking it by means of     
drugs4 ,but after a little1 conditions  
arise which are hostile to the further  
growth of the parasite4 ,these hostile  
conditions are produced perhaps in part 
by the secretions from the bacteria1 for
 bacteria are unable to flourish in a   
medium containing much of their own     
secretions4 ,the secretions which they  
produce are poisons to them as well as  

to the individual in which they grow1   
and after these have become quite       
abundant the further growth of the      
bacterium is checked and finally        
stopped4 ,partly1 also1 must we conclude
 that these hostile conditions are      
produced by active vital powers in the  
body of the individual attacked4 ,the   
individual1 as we have seen1 in some    
cases develops a quantity of some       
substance which neutralizes the         
bacterial poisons and thus prevents     
their having their maximum effect4 ,thus
 relieved from the direct effects of the
 poisons1 the resisting powers are      
recuperated and once more begin to      
produce a direct destruction of the     
bacteria4 ,possibly the bacteria1 being 
now weakened by the presence of their   
own products of growth1 more readily    
yield to the resisting forces of the    
cell life of the body4 ,possibly the    
resisting forces are decidedly increased
 by the reactive effect of the bacteria 
and their poisons4 ,but1 at all events1 

in cases where recovery from parasitic  
diseases occurs1 the revived powers of  
resistance finally overcome the         
bacteria1 destroy them or drive them    
off1 and the body recovers4  ,all this  
is1 of course1 a natural process4 ,the  
recovery from a disease produced by the 
invasion of parasitic bacteria depends  
upon whether the body can resist the    
bacterial poisons long enough for the   
recuperation of its resisting powers4   
,if these poisons are very violent and  
produced rapidly1 death will probably   
occur before the resisting powers are   
strong enough to drive off the bacteria4
 ,in the case of some diseases the      
poisons are so violent that this        
practically always occurs1 recovery     
being very exceptional4 ,the poison     
produced by the tetanus bacillus is of  
this nature1 and recovery from lockjaw  
is of the rarest occurrence4 ,but in    
many other diseases the body is able to 
withstand the poison1 and later to      
recover its resisting powers            

sufficiently to drive off the invaders4 
,in all cases1 however1 the process is a
 natural one and dependent upon the     
vital activity of the body4 ,it is based
 at the foundation1 doubtless1 upon the 
powers of the body cells1 either the    
phagocytes or other active cells4 ,the  
body has1 in short1 its own forces for  
repelling invasions1 and upon these     
forces must we depend for the power to  
produce recovery4  ,it is evident that  
all these facts give us very little     
encouragement that we shall ever be able
 to cure diseases directly by means of  
drugs to destroy bacteria1 but1 on the  
contrary1 that we must ever depend upon 
the resisting powers of the body4 ,they 
teach us1 moreover1 along what line we  
must look for the future development of 
curative medicine4 ,it is evident that  
scientific medicine must turn its       
attention toward the strengthening and  
stimulating of the resisting and        
curative forces of the body4 ,it must be
 the physician's aim to enable the body 

to resist the poisons as well as        
possible and to stimulate it to         
re-enforce its resistant forces4 ,drugs 
have a place in medicine1 of course1 but
 this place is chiefly to stimulate the 
body to react against its invading      
hosts4 ,they are1 as a rule1 not        
specific against definite diseases4 ,we 
can not hope for much in the way of     
discovering special medicines adapted to
 special diseases4 ,we must simply look 
upon them as means which the physician  
has in hand for stimulating the natural 
forces of the body1 and these may       
doubtless vary with different individual
 natures4 ,recognising this1 we can see 
also the logic of the small dose as     
compared to the large dose4 ,a small    
dose of a drug may serve as a stimulant 
for the lagging forces1 while a larger  
dose would directly repress them or     
produce injurious secondary effects4 ,as
 soon as we recognise that the aim of   
medicine is not to destroy the disease  
but rather to stimulate the resisting   

forces of the body1 the whole logic of  
therapeutics assumes a new aspect4      
,physicians have understood this1 and1  
especially in recent years1 have guided 
their practice by it4 ,if a moderate    
dose of quinine will check malaria in a 
few days1 it does not follow that twice 
the dose will do it in half the time or 
with twice the certainty4 ,the larger   
doses of the past1 intended to drive out
 the disease1 have been everywhere      
replaced by smaller doses designed to   
stimulate the lagging body powers4 ,the 
modern physician makes no attempt to    
cure typhoid fever1 having long since   
learned his inability to do this1 at    
least if the fever once gets a foothold2
 but he turns his attention to every    
conceivable means of increasing the     
body's strength to resist the typhoid   
poison1 confident that if he can thus   
enable the patient to resist the        
poisoning effects of the typhotoxine his
 patient will in the end react against  
the disease and drive off the invading  

bacteria4 ,the physician's duty is to   
watch and guard1 but he must depend upon
 the vital powers of his patient to     
carry on alone the actual battle with   
the bacterial invaders4  ,,antitoxines4 
,in very recent times1 however1 our     
bacteriologists have been pointing out  
to the world certain entirely new means 
of assisting the body to fight its      
battles with bacterial diseases4 ,as    
already noticed1 one of the primal      
forces in the recovery1 from some       
diseases1 at least1 is the development  
in the body of a substance which acts as
 an antidote to the bacterial poison4   
,so long as this antitoxine is not      
present the poisons produced by the     
disease will have their full effect to  
weaken the body and prevent the revival 
of its resisting powers to drive off the
 bacteria4 ,plainly1 if it is possible  
to obtain this antitoxine in quantity   
and then inoculate it into the body when
 the toxic poisons are present1 we have 
a means for decidedly assisting the body

 in its efforts to drive off the        
parasites4 ,such an antidote to the     
bacterial poison would not1 indeed1     
produce a cure1 but it would perhaps    
have the effect of annulling the action 
of the poisons1 and would thus give the 
body a much greater chance to master the
 bacteria4 ,it is upon this principle   
that is based the use of antitoxines in 
diphtheria and tetanus  ,it will be     
clear that to obtain the antitoxine we  
must depend upon some natural method for
 its production4 ,we do not know enough 
of the chemical nature of the           
antitoxines to manufacture them         
artificially4 ,of course we can not deny
 the possibility of their artificial    
production1 and certain very recent     
experiments indicate that perhaps they  
may be made by the agency of            
electricity4 ,at present1 however1 we   
must use natural methods1 and the one   
commonly adopted is simple4 ,some animal
 is selected whose blood is harmless to 
man and that is subject to the disease  

to be treated4 ,for diphtheria a horse  
is chosen4 ,this animal is inoculated   
with small quantities of the diphtheria 
poison without the diphtheria bacillus4 
,this poison is easily obtained by      
causing the diphtheria bacillus to grow 
in common media in the laboratory for a 
while1 and the toxines develop in       
quantity2 then1 by proper filtration1   
the bacteria themselves can be removed1 
leaving a pure solution of the toxic    
poison4 ,small quantities of this poison
 are inoculated into the horse at       
successive intervals4 ,the effect on the
 horse is the same as if the animal had 
the disease4 ,its cells react and       
produce a considerable quantity of the  
antitoxine which remains in solution in 
the blood of the animal4 ,this is not   
theory1 but demonstrated fact4 ,the     
blood of a horse so treated is found to 
have the effect of neutralizing the     
diphtheria poison1 although the blood of
 the horse before such treatment has no 
such effect4 ,thus there is developed in

 the horse's blood a quantity of the    
antitoxine1 and now it may be used by   
physicians where needed4 ,if some of    
this horse's blood1 properly treated1 be
 inoculated into the body of a person   
who is suffering from diphtheria1 its   
effect1 provided the theory of          
antitoxines is true1 will be to         
counteract in part1 at least1 the       
poisons which are being produced in the 
patient by the diphtheria bacillus4     
,this does not cure the disease nor in  
itself drive off the bacilli1 but it    
does protect the body from the poisons  
to such an extent as to enable it more  
readily to assert its own resisting     
powers4  ,this method of using          
antitoxines as a help in curing disease 
is very recent1 and we can not even     
guess what may come of it4 ,it has      
apparently been successfully applied in 
diphtheria4 ,it has also been used in   
tetanus with slight success4 ,the same  
principle has been used in obtaining an 
antidote for the poison of snake bites1 

since it has appeared that in this kind 
of poisoning the body will develop an   
antidote to the poison if it gets a     
chance4 ,horses have been treated in the
 same way as with the diphtheria poison1
 and in the same way they develop a     
substance which neutralizes the snake   
poison4 ,other diseases are being       
studied to-day with the hope of similar 
results4 ,how much further the principle
 will go we can not say1 nor can we be  
very confident that the same principle  
will apply very widely4 ,the parasitic  
diseases are so different in nature that
 we can hardly expect that a method     
which is satisfactory in meeting one of 
the diseases will be very likely to be  
adapted to another4 ,vaccination has    
proved of value in smallpox1 but is not 
of use in other human diseases4         
,inoculation with weakened germs has    
proved of value in anthrax and fowl     
cholera1 but will not apply to all      
diseases4 ,each of these parasites must 
be fought by special methods1 and we    

must not expect that a method that is of
 value in one case must necessarily be  
of use elsewhere4 ,above all1 we must   
remember that the antitoxines do not    
cure in themselves2 they only guard the 
body from the weakening effects of the  
poisons until it can cure itself1 and1  
unless the body has resisting powers1   
the antitoxine will fail to produce the 
desired results4  ,one further point in 
the action of the antitoxines must be   
noticed4 ,as we have seen1 a recovery   
from an attack of most germ diseases    
renders the individual for a time immune
 against a second attack4 ,this applies 
less1 however1 to a recovery after the  
artificial inoculation with antitoxine  
than when the individual recovers       
without such aid4 ,if the individual    
recovers quite independently of the     
artificial antitoxine1 he does so in    
part because he has developed the       
antitoxines for counteracting the poison
 by his own powers4 ,his cellular       
activities have1 in other words1 been   

for a moment at least turned in the     
direction of production of antitoxines4 
,it is to be expected1 therefore1 that  
after the recovery they will still have 
this power1 and so long as they possess 
it the individual will have protection  
from a second attack4 ,when1 however1   
the recovery results from the artificial
 inoculation of antitoxine the body     
cells have not actively produced        
antitoxine4 ,the neutralization of the  
poisons has been a passive one1 and     
after recovery the body cells are no    
more engaged in producing antitoxine    
than before4 ,the antitoxine which was  
inoculated is soon eliminated by        
secretion1 and the body is left with    
practically the same liability to attack
 as before4 ,its immunity is decidedly  
fleeting1 since it was dependent not    
upon any activity on the part of the    
body1 but upon an artificial inoculation
 of a material which is rapidly         
eliminated by secretion4  ,,conclusion4 
,it is hoped that the outline which has 

been given of the bacterial life of     
,nature may serve to give some adequate 
idea of these organisms and correct the 
erroneous impressions in regard to them 
which are widely prevalent4 ,it will be 
seen that1 as our friends1 bacteria play
 a vastly more important part in ,nature
 than they do as our enemies4 ,these    
plants are minute and extraordinarily   
simple1 but1 nevertheless1 there exists 
a large number of different species4    
,the number of described forms already  
runs far into the hundreds1 and we do   
not yet appear to be approaching the end
 of them4 ,they are everywhere in       
,nature1 and their numbers are vast     
beyond conception4 ,their powers of     
multiplication are inconceivable1 and   
their ability to produce profound       
chemical changes is therefore unlimited4
 ,this vast host of living beings thus  
constitutes a force or series of forces 
of tremendous significance4 ,most of the
 vast multitude we must regard as our   
friends4 ,upon them the farmer is       

dependent for the fertility of his soil 
and the possibility of continued life in
 his crops4 ,upon them the dairyman is  
dependent for his flavours4 ,upon them  
important fermentative industries are   
dependent1 and their universal powers   
come into action upon a commercial scale
 in many a place where we have little   
thought of them in past years4 ,we must 
look upon them as agents ever at work1  
by means of which the surface of ,nature
 is enabled to remain fresh and green4  
,their power is fundamental1 and their  
activities are necessary for the        
continuance of life4 ,a small number of 
the vast host1 a score or two of        
species1 unfortunately for us1 find     
their most favourable living place in   
the human body1 and thus become human   
parasites4 ,by their growth they develop
 poisons and produce disease4 ,this     
small class of parasites are then       
decidedly our enemies4 ,but1 taken all  
together1 we must regard the bacteria as
 friends and allies4 ,without them we   

should not have our epidemics1 but      
without them we should not exist4       
,without them it might be that some     
individuals would live a little longer1 
if indeed we could live at all4 ,it is  
true that bacteria1 by producing        
disease1 once in a while cause the      
premature death of an individual2 once  
in a while1 indeed1 they may sweep off a
 hundred or a thousand individuals2 but 
it is equally true that without them    
plant and animal life would be          
impossible on the face of the earth4