,,outlines ,,of ,,dairy ,,bacteriology ,a ,,concise ,,manual ,,for ,,the ,,use ,,of ,,students ,,in ,,dairying ,,by ,h4 ,l4 ,,russell ,,dean ,,of ,,the ,,college ,,of ,,agriculture1 ,,university ,,of ,,wisconsin ,,eighth ,,edition ,,thoroughly ,,revised ,,madison1 ,,wisconsin ,h4 ,l4 ,,russell #aijg ,copyrighted #aije ,,by ,h4 ,l4 ,,russell ,,state ,,journal ,,printing ,,company1 ,printers ,and ,stereotypers1 ,madison1 ,wis4 ,transcriber's note3 ,for ,text3 ,a word surrounded by a cedilla such as this signifies that the word is bolded in the text4 ,a word surrounded by underscores like this signifies the word is italics in the text4 ,for numbers and equations1 underscores before bracketed numbers in equations denote a subscript4 ,minor typos have been corrected4 ,,preface4 ,knowledge in dairying1 like all other technical industries1 has grown mainly out of experience4 ,many facts have been learned by observation1 but the why of each is frequently shrouded in mystery4 ,modern dairying is attempting to build its more accurate knowledge upon a broader and surer foundation1 and in doing this is seeking to ascertain the cause of well-established processes4 ,in this1 bacteriology is playing an important role4 ,indeed1 it may be safely predicted that future progress in dairying will1 to a large extent1 depend upon bacteriological research4 ,as ,fleischmann1 the eminent ,german dairy scientist1 says3 ,the gradual abolition of uncertainty surrounding dairy manufacture is the present important duty which lies before us1 and its solution can only be effected by bacteriology4 ,it is therefore natural that the subject of ,dairy ,bacteriology has come to occupy an important place in the curriculum of almost every ,dairy ,school4 ,an exposition of its principles is now recognized as an integral part of dairy science1 for modern dairy practice is rapidly adopting the methods that have been developed as the result of bacteriological study4 ,the rapid development of the subject has necessitated a frequent revision of this work1 and it is gratifying to the writer that the attempt which has been made to keep these ,outlines abreast of bacteriological advance has been appreciated by students of dairying4 ,while the text is prepared more especially for the practical dairy operator who wishes to understand the principles and reasons underlying his art1 numerous references to original investigations have been added to aid the dairy investigator who wishes to work up the subject more thoroughly4 ,my acknowledgments are due to the following for the loan of illustrations3 ,wisconsin ,agricultural ,experiment ,station2 ,creamery ,package ,mfg4 ,co41 ,chicago1 ,ill42 and ,a4 ,h4 ,reid1 ,philadelphia1 ,pa4 ,h4 ,l4 ,russell4 ,university of ,wisconsin4 ,,contents4 ,,chapter ,i4 ,structure of the bacteria and conditions governing their development and distribution #a ,,chapter ,,ii4 ,methods of studying bacteria #ac ,,chapter ,,iii4 ,contamination of milk #ai ,,chapter ,,iv4 ,fermentations in milk and their treatment #fb ,,chapter ,v4 ,relation of disease-bacteria to milk #hb ,diseases transmissible from animal to man through diseased milk #hd ,diseases transmissible to man through infection of milk after withdrawal #id ,,chapter ,,vi4 ,preservation of milk for commercial purposes #ajb ,,chapter ,,vii4 ,bacteria and butter making #acd ,bacterial defects in butter #aef ,,chapter ,,viii4 ,bacteria in cheese #afj ,influence ,of bacteria in normal cheese processes #afj ,influence of bacteria in abnormal cheese processes #ahb ,,chapter ,i4 ,,structure ,,of ,,the ,,bacteria ,,and ,,conditions ,,governing ,,their ,,development ,,and ,,distribution4 ,before one can gain any intelligent conception of the manner in which bacteria affect dairying1 it is first necessary to know something of the life history of these organisms in general1 how they live1 move and react toward their environment4 ,nature of ,bacteria4 ,toadstools1 smuts1 rusts and mildews are known to even the casual observer1 because they are of evident size4 ,their plant-like nature can be more readily understood from their general structure and habits of life4 ,the bacteria1 however1 are so small1 that under ordinary conditions1 they only become evident to our unaided senses by the by-products of their activity4 ,when ,leeuwenhoek 7pronounced ,lave-en-hake7 in #afge first discovered these tiny1 rapidly-moving organisms he thought they were animals4 ,indeed1 under a microscope1 many of them bear a close resemblance to those minute worms found in vinegar that are known as vinegar-eels4 ,the idea that they belonged to the animal kingdom continued to hold ground until after the middle of the nineteenth century2 but with the improvement in microscopes1 a more thorough study of these tiny structures was made possible1 and their vegetable nature demonstrated4 ,the bacteria as a class are separated from the fungi mainly by their method of growth2 from the lower algae by the absence of chlorophyll1 the green coloring matter of vegetable organisms4 ,structure of bacteria4 ,so far as structure is concerned the bacteria stand on the lowest plane of vegetable life4 ,the single individual is composed of but a single cell1 the structure of which does not differ essentially from that of many of the higher types of plant life4 ,it is composed of a protoplasmic body which is surrounded by a thin membrane that separates it from neighboring cells that are alike in form and size4 ,form and size4 ,when a plant is composed of a single cell but little difference in form is to be expected4 ,while there are intermediate stages that grade insensibly into each other1 the bacteria may be grouped into three main types1 so far as form is concerned4 ,these are spherical1 elongated1 and spiral1 and to these different types are given the names1 respectively1 coccus1 bacillus and spirillum 7plural1 cocci1 bacilli1 spirilla7 7fig4 #a74 ,a ball1 a short rod1 and a corkscrew serve as convenient models to illustrate these different forms4 ,illustration3 ,,fig4 #a4 ,different forms of bacteria4 a1 b1 c1 represent different types as to form3 a1 coccus1 b1 bacillus1 c1 spirillum2 d1 diplococcus or twin coccus2 e1 staphylococcus or cluster coccus2 f and g1 different forms of bacilli1 g shows internal endospores within cell2 h and i1 bacilli with motile organs 7cilia74 ,in size1 the bacteria are the smallest organisms that are known to exist4 ,relatively there is considerable difference in size between the different species1 yet in absolute amount this is so slight as to require the highest powers of the microscope to detect it4 ,as an average diameter1 one thirty-thousandth of an inch may be taken4 ,it is difficult to comprehend such minute measurements1 but if a hundred individual germs could be placed side by side1 their total thickness would not equal that of a single sheet of paper upon which this page is printed4 ,manner of ,growth4 ,as the cell increases in size as a result of growth1 it elongates in one direction1 and finally a new cell wall is formed1 dividing the so-called mother-cell into two1 equal-sized daughter-cells4 ,this process of cell division1 known as fission1 is continued until growth ceases and is especially characteristic of bacteria4 ,cell ,arrangement4 ,if fission goes on in the same plane continually1 it results in the formation of a cell-row4 ,a coccus forming such a chain of cells is called strepto-coccus 7chain-coccus74 ,if only two cells cohere1 it is called a diplo-coccus 7twin-coccus74 ,if the second cell division plane is formed at right angles to the first1 a cell surface or tetrad is formed4 ,if growth takes place in three dimensions of space1 a cell mass or sarcina is produced4 ,frequently1 these cell aggregates cohere so tenaciously that this arrangement is of value in distinguishing different species4 ,spores4 ,some bacteria possess the property of forming spores within the mother cell 7called endospores1 fig4 #a;g7 that are analogous in function to the seeds of higher plants and spores of fungi4 ,by means of these structures which are endowed with greater powers of resistance than the vegetating cell1 the organism is able to protect itself from the effect of an unfavorable environment4 ,many of the bacilli form endospores but the cocci do not4 ,it is these spore forms that make it so difficult to thoroughly sterilize milk4 ,movement4 ,many bacteria are unable to move from place to place4 ,they have1 however1 a vibrating movement known as the ,brownian motion that is purely physical4 ,many other kinds are endowed with powers of locomotion4 ,motion is produced by means of fine thread-like processes of protoplasm known as cilia 7sing4 cilium7 that are developed on the outer surface of the cell4 ,by means of the rapid vibration of these organs1 the cell is propelled through the medium4 ,nearly all cocci are immotile1 while the bacilli may or may not be4 ,these cilia are so delicate that it requires special treatment to demonstrate their presence4 ,classification4 ,in classifying or arranging the different members of any group of living objects1 certain similarities and dissimilarities must be considered4 ,these are usually those that pertain to the structure and form1 as such are regarded as most constant4 ,with the bacteria these differences are so slight that they alone do not suffice to distinguish distinctly one species from another4 ,as far as these characters can be used1 they are taken1 but in addition1 many characteristics of a physiological nature are added4 ,the way that the organism grows in different kinds of cultures1 the by-products produced in different media1 and effect on the animal body when injected into the same are also used as data in distinguishing one species from another4 ,conditions favoring bacterial growth4 ,the bacteria1 in common with all other living organisms are affected by external conditions1 either favorably or unfavorably4 ,certain conditions must prevail before development can occur4 ,thus1 the organism must be supplied with an adequate and suitable food supply and with moisture4 ,the temperature must also range between certain limits1 and finally1 the oxygen requirements of the organism must be considered4 ,food supply4 ,most bacteria are capable of living on dead1 inert1 organic matter1 such as meats1 milk and vegetable material1 in which case1 they are known as saprophytes4 ,in contradistinction to this class is a smaller group known as parasites1 which derive their nourishment from the living tissues of animals or plants4 ,the first group comprise by far the larger number of known organisms which are concerned for the most part in the decomposition of organic matter4 ,the parasitic group includes those which are the cause of various communicable diseases4 ,between these two groups there is no sharp line of division1 and in some cases1 certain species possess the faculty of growing either as parasites or saprophytes1 in which case they are known as facultative parasites or saprophytes4 ,the great majority of bacteria of interest in dairying belong to the saprophytic class2 only those species capable of infecting milk through the development of disease in the animal are parasites in the strict sense of the term4 ,most disease-producing species1 as diphtheria or typhoid fever1 while parasitic in man lead a saprophytic method of life so far as their relation to milk is concerned4 ,bacteria require for their growth1 nitrogen1 hydrogen1 carbon1 oxygen1 together with a limited amount of mineral matter4 ,the nitrogen and carbon are most available in the form of organic compounds1 such as albuminous material4 ,carbon in the form of carbohydrates1 as sugar or starch1 is most readily attacked by bacteria4 ,inasmuch as the bacteria are plant-cells1 they must imbibe their food from material in solution4 ,they are capable of living on solid substances1 but in such cases1 the food elements must be rendered soluble1 before they can be appropriated4 ,if nutritive liquids are too highly concentrated1 as in the case of syrups and condensed milk1 bacteria cannot grow therein1 although all the necessary ingredients may be present4 ,generally1 bacteria prefer a neutral or slightly alkaline medium1 rather than one of acid reaction2 but there are numerous exceptions to this general rule1 especially among the bacteria found in milk4 ,temperature4 ,growth of bacteria can only occur within certain temperature limits1 the extremes of which are designated as the minimum and maximum4 ,below and above these respective limits1 life may be retained in the cell for a time1 but actual cell-multiplication is stopped4 ,somewhere between these two cardinal temperature points1 and generally nearer the maximum limit is the most favorable temperature for growth1 known as the optimum4 ,the temperature zone of most dairy bacteria in which growth occurs ranges from #dj deg4-#de deg4 ,f4 to somewhat above blood-heat1 #aje deg4-#aaj deg4 ,f41 the optimum being from #hj deg4-#ie deg4 ,f4 ,many parasitic species1 because of their adaptation to the bodies of warm-blooded animals1 generally have a narrower range1 and a higher optimum1 usually approximating the blood heat 7#ih deg4-#ii deg4 ,f74 ,the broader growth limits of bacteria in comparison with other kinds of life explain why these organisms are so widely distributed in nature4 ,air supply4 ,most bacteria require as do the green plants and animal life1 the free oxygen of the air for their respiration4 ,these are called aerobic4 ,some species1 however1 and some yeasts as well possess the peculiar property of taking the oxygen which they need from organic compounds such as sugar1 etc41 and are therefore able to live and grow under conditions where the atmospheric air is excluded4 ,these are known as anaerobic4 ,while some species grow strictly under one condition or the other1 and hence are obligate aerobes or anaerobes1 others possess the ability of growing under either condition and are known as facultative or optional forms4 ,the great majority of milk bacteria are either obligate or facultative aerobes4 ,rate of growth4 ,the rate of bacterial development is naturally very much affected by external conditions1 food supply and temperature exerting the most influence4 ,in the neighborhood of the freezing point but little growth occurs4 ,the rate increases with a rise in temperature until at the optimum point1 which is generally near the blood heat or slightly below 7#ij deg4-#ih deg4 ,f471 a single cell will form two cells in #bj to #cj minutes4 ,if temperature rises much above blood heat rate of growth is lessened and finally ceases4 ,under ideal conditions1 rapidity of growth is astounding1 but this initially rapid rate of development cannot be maintained indefinitely1 for growth is soon limited by the accumulation of by-products of cell activity4 ,thus1 milk sours rapidly at ordinary temperatures until the accumulation of acid checks its development4 ,detrimental effect of external conditions4 ,environmental influences of a detrimental character are constantly at work on bacteria1 tending to repress their development or destroy them4 ,these act much more readily on the vegetating cell than on the more resistant spore4 ,a thorough knowledge of the effect of these antagonistic forces is essential1 for it is often by their means that undesirable bacteria may be killed out4 ,effect of cold4 ,while it is true that chilling largely prevents fermentative action1 and actual freezing stops all growth processes1 still it does not follow that exposure to low temperatures will effectually destroy the vitality of bacteria1 even in the vegetative condition4 ,numerous non-spore-bearing species remain alive in ice for a prolonged period1 and recent experiments with liquid air show that even a temperature of -#caj deg4 ,f4 for hours does not effectually kill all exposed cells4 ,effect of heat4 ,high temperatures1 on the other hand1 will destroy any form of life1 whether in the vegetative or latent stage4 ,the temperature at which the vitality of the cell is lost is known as the thermal death point4 ,this limit is not only dependent upon the nature of the organism1 but varies with the time of exposure and the condition in which the heat is applied4 ,in a moist atmosphere the penetrating power of heat is great2 consequently cell-death occurs at a lower temperature than in a dry atmosphere4 ,an increase in time of exposure lowers the temperature point at which death occurs4 ,for vegetating forms the thermal death point of most bacteria ranges from #acj deg4-#adj deg4 ,f4 where the exposure is made for ten minutes which is the standard arbitrarily selected4 ,in the spore stage resistance is greatly increased1 some forms being able to withstand steam at #baj deg4-#bab deg4 ,f4 from one to three hours4 ,if dry heat is employed1 #bfj deg4-#cjj deg4 ,f4 for an hour is necessary to kill spores4 ,where steam is confined under pressure1 a temperature of #bcj deg4-#bdj deg4 ,f4 for #ae-bj minutes suffices to kill all spores4 ,drying4 ,spore-bearing bacteria like anthrax withstand drying with impunity2 even tuberculous material1 although not possessing spores retains its infectious properties for many months4 ,most of the dairy bacteria do not produce spores1 and yet in a dry condition1 they retain their vitality unimpaired for considerable periods1 if they are not subjected to other detrimental influences4 ,light4 ,bright sunlight exerts on many species a powerful disinfecting action1 a few hours being sufficient to destroy all cells that are reached by the sun's rays4 ,even diffused light has a similar effect1 although naturally less marked4 ,the active rays in this disinfecting action are those of the chemical or violet end of the spectrum1 and not the heat or red rays4 ,influence of chemical substances4 ,a great many chemical substances exert a more or less powerful toxic action of various kinds of life4 ,many of these are of great service in destroying or holding bacterial growth in check4 ,those that are toxic and result in the death of the cell are known as disinfectants2 those that merely inhibit1 or retard growth are known as antiseptics4 ,all disinfectants must of necessity be antiseptic in their action1 but not all antiseptics are disinfectants even when used in strong doses4 ,disinfectants have no place in dairy work1 except to destroy disease bacteria1 or preserve milk for analytical purposes4 ,corrosive sublimate or potassium bichromate are most frequently used for these purposes4 ,the so-called chemical preservatives used to keep milk depend for their effect on the inhibition of bacterial growth4 ,with a substance so violently toxic as formaldehyde 7known as formalin1 freezene7 antiseptic doses are likely to be exceeded4 ,in this country most states prohibit the use of these substances in milk4 ,their only function in the dairy should be to check fermentative or putrefactive processes outside of milk and so keep the air free from taints4 ,products of growth4 ,all bacteria in their development form certain more or less characteristic by-products4 ,with most dairy bacteria1 these products are formed from the decomposition of the medium in which the bacteria may happen to live4 ,such changes are known1 collectively1 as fermentations1 and are characterised by the production of a large amount of by-products1 as a result of the development of a relatively small amount of cell-life4 ,the souring of milk1 the formation of butyric acid1 the making of vinegar from cider1 are all examples of fermentative changes4 ,with many bacteria1 especially those that affect proteid matter1 foul-smelling gases are formed4 ,these are known as putrefactive changes4 ,all organic matter1 under the action of various organisms1 sooner or later undergoes decay1 and in different stages of these processes1 acids1 alkalies1 gases and numerous other products are formed4 ,many of these changes in organic matter occur only when such material is brought in direct contact with the living bacterial cell4 ,in other instances1 soluble1 non-vital ferments known as enzyms are produced by the living cell1 which are able to act on organic matter1 in a medium free from live cells1 or under conditions where the activity of the cell is wholly suspended4 ,these enzyms are not confined to bacteria but are found throughout the animal and plant world1 especially in those processes that are concerned in digestion4 ,among the better known of these non-vital ferments are rennet1 the milk-curdling enzym2 diastase or ptyalin of the saliva1 the starch-converting enzym2 pepsin and trypsin1 the digestive ferments of the animal body4 ,enzyms of these types are frequently found among the bacteria and yeasts and it is by virtue of this characteristic that these organisms are able to break down such enormous quantities of organic matter4 ,most of these enzyms react toward heat1 cold and chemical poisons in a manner quite similar to the living cells4 ,in one respect they are readily differentiated1 and that is1 that practically all of them are capable of producing their characteristic chemical transformations under anaesthetic conditions1 as in a saturated ether or chloroform atmosphere4 ,distribution of bacteria4 ,as bacteria possess greater powers of resistance than most other forms of life1 they are to be found more widely distributed than any other type4 ,at the surface of the earth1 where conditions permit of their growth1 they are found everywhere1 except in the healthy tissues of animals and plants4 ,in the superficial soil layers1 they exist in myriads1 as here they have abundance of nourishment4 ,at the depth of several feet however1 they diminish rapidly in numbers1 and in the deeper soil layers1 from six to ten feet or more1 they are not present1 because of the unsuitable growth conditions4 ,the bacteria are found in the air because of their development in the soil below4 ,they are unable to grow even in a moist atmosphere1 but are so readily dislodged by wind currents that over land areas the lower strata of the air always contain them4 ,they are more numerous in summer than in winter2 city air contains larger numbers than country air4 ,wherever dried fecal matter is present1 as in barns1 the air contains many forms4 ,water contains generally enough organic matter in solution1 so that certain types of bacterial life find favorable growth conditions4 ,water in contact with the soil surface takes up many impurities1 and is of necessity rich in microbes4 ,as the rain water percolates into the soil1 it loses its germ content1 so that the normal ground water1 like the deeper soil layers1 contains practically no bacterial life4 ,springs therefore are relatively deficient in germ life1 except as they become infected with soil organisms1 as the water issues from the soil4 ,water may serve to disseminate certain infectious diseases as typhoid fever and cholera among human beings1 and a number of animal maladies4 ,while the inner tissues of healthy animals are free from bacteria1 the natural passages as the respiratory and digestive tracts1 being in more direct contact with the exterior1 become more readily infected4 ,this is particularly true with reference to the intestinal tract1 for in the undigested residue1 bacterial activity is at a maximum4 ,the result is that fecal matter contains enormous numbers of organisms so that the possibility of pollution of any food medium such as milk with such material is sure to introduce elements that seriously affect the quality of the product4 ,,chapter ,,ii4 ,,methods ,,of ,,studying ,,bacteria4 ,necessity of bacterial masses for study4 ,the bacteria are so extremely small that it is impossible to study individual germs separately without the aid of first-class microscopes4 ,for this reason1 but little advance was made in the knowledge of these lower forms of plant life1 until the introduction of culture methods1 whereby a single organism could be cultivated and the progeny of this cell increased to such an extent in a short course of time1 that they would be visible to the unaided eye4 ,this is done by growing the bacteria in masses on various kinds of food media that are prepared for the purpose1 but inasmuch as bacteria are so universally distributed1 it becomes an impossibility to cultivate any special form1 unless the medium in which they are grown is first freed from all pre-existing forms of germ life4 ,to accomplish this1 it is necessary to subject the nutrient medium to some method of sterilization1 such as heat or filtration1 whereby all life is completely destroyed or eliminated4 ,such material after it has been rendered germ-free is kept in sterilized glass tubes and flasks1 and is protected from infection by cotton stoppers4 ,culture media4 ,for culture media1 many different substances are employed4 ,in fact1 bacteria will grow on almost any organic substance whether it is solid or fluid1 provided the other essential conditions of growth are furnished4 ,the food substances that are used for culture purposes are divided into two classes2 solids and liquids4 ,solid media may be either permanently solid like potatoes1 or they may retain their solid properties only at certain temperatures like gelatin or agar4 ,the latter two are of utmost importance in bacteriological research1 for their use1 which was introduced by ,koch1 permits the separation of the different forms that may happen to be in any mixture4 ,gelatin is used advantageously because the majority of bacteria present wider differences due to growth upon this medium than upon any other4 ,it remains solid at ordinary temperatures1 becoming liquid at about #gj deg4 ,f4 ,agar1 a gelatinous product derived from a ,japanese sea-weed1 has a much higher melting point1 and can be successfully used1 especially with those organisms whose optimum growth point is above the melting point of gelatin4 ,besides these solid media1 different liquid substances are extensively used1 such as beef broth1 milk1 and infusions of various vegetable and animal tissues4 ,skim-milk is of especial value in studying the milk bacteria and may be used in its natural condition1 or a few drops of litmus solution may be added in order to detect any change in its chemical reaction due to the bacteria4 ,illustration3 ,,fig4 #b4 ,a gelatin plate culture showing appearance of different organisms in a sample of milk4 ,each mass represents a bacterial growth 7colony7 derived from a single cell4 ,different forms react differently toward the gelatin1 some liquefying the same1 others growing in a restricted mass4 a1 represents a colony of the ordinary bread mold2 b1 a liquefying bacterium2 c1 and d1 solid forms4 ,methods of isolation4 ,suppose for instance one wishes to isolate the different varieties of bacteria found in milk4 ,the method of procedure is as follows3 ,sterile gelatin in glass tubes is melted and cooled down so as to be barely warm4 ,to this gelatin which is germ-free a drop of milk is added4 ,the gelatin is then gently shaken so as to thoroughly distribute the milk particles1 and poured out into a sterile flat glass dish and quickly covered4 ,this is allowed to stand on a cool surface until the gelatin hardens4 ,after the culture plate has been left for twenty-four to thirty-six hours at the proper temperature1 tiny spots will begin to appear on the surface1 or in the depth of the culture medium4 ,these patches are called colonies and are composed of an almost infinite number of individual germs1 the result of the continued growth of a single organism that was in the drop of milk which was firmly held in place when the gelatin solidified4 ,the number of these colonies represents approximately the number of germs that were present in the milk drop4 ,if the plate is not too thickly sown with these germs1 the colonies will continue to grow and increase in size1 and as they do1 minute differences will begin to appear4 ,these differences may be in the color1 the contour and the texture of the colony1 or the manner in which it acts toward gelatin4 ,in order to make sure that the seeding in not too copious so as to interfere with continued study1 an attenuation is usually made4 ,this consists in taking a drop of the infected gelatin in the first tube1 and transferring it to another tube of sterile media4 ,usually this operation is repeated again so that these culture plates are made with different amounts of seed with the expectation that in at least one plate the seeding will not be so thick as to prevent further study4 ,for transferring the culture a loop made of platinum wire is used4 ,by passing this through a gas flame1 it can be sufficiently sterilized4 ,illustration3 ,,fig4 #c4 ,profile view of gelatin plate culture2 b1 a liquefying form that dissolves the gelatin2 c and d1 surface colonies that do not liquefy the gelatin4 ,to further study the peculiarities of different germs1 the separate colonies are transferred to other sterile tubes of culture material and thus pure cultures of the various germs are secured4 ,these cultures then serve as a basis for continued study and must be planted and grown upon all the different kinds of media that are obtainable4 ,in this way the slight variations in the growth of different forms are detected and the peculiar characteristics are determined1 so that the student is able to recognize this form when he meets it again4 ,these culture methods are of essential importance in bacteriology1 as it is the only way in which it is possible to secure a quantity of germs of the same kind4 ,the microscope in bacterial investigation4 ,in order to verify the purity of the cultures1 the microscope is in constant demand throughout all the different stages of the isolating process4 ,for this purpose1 it is essential that the instrument used shall be one of strong magnifying powers 7#fjj-hjj diameters71 combined with sharp definition4 ,illustration3 ,,fig4 #d4 ,pure cultures of different kinds of bacteria in gelatin tubes4 a1 growth slight in this medium2 b1 growth copious at and near surface4 ,fine parallel filaments growing out into medium liquefying at surface2 c1 a rapid liquefying form2 d1 a gas-producing form that grows equally well in lower part of tube as at surface 7facultative anaerobe72 e1 an obligate anaerobe1 that develops only in absence of air4 ,the microscopical examination of any germ is quite as essential as the determination of culture characteristics2 in fact1 the two must go hand in hand4 ,the examination reveals not only the form and size of the individual germs1 but the manner in which they are united with each other1 as well as any peculiarities of movement that they may possess4 ,in carrying out the microscopical part of the work1 not only is the organism examined in a living condition1 but preparations are made by using solutions of anilin dyes as staining agents4 ,these are of great service in bringing out almost imperceptible differences4 ,the art of staining has been carried to the highest degree of perfection in bacteriology1 especially in the detection of germs that are found in diseased tissues in the animal or human body4 ,in studying the peculiarities of any special organism1 not only is it necessary that these cultural and microscopical characters should be closely observed1 but special experiments must be carried out along different lines1 in order to determine any special properties that the germ may possess4 ,thus1 the ability of any form to act as a fermentative organism can be tested by fermentation experiments2 the property of causing disease1 studied by the inoculation of pure cultures into animals4 ,a great many different methods have been devised for the purpose of studying special characteristics of different bacteria1 but a full description of these would necessarily be so lengthy that in a work of this character they must be omitted4 ,for details of this nature consult standard reference books on bacteriological technique4 ,,chapter ,,iii4 ,,contamination ,,of ,,milk4 ,no more important lesson is to be learned than that which relates to the ways in which milk is contaminated with germ life of various kinds2 for if these sources of infection are thoroughly recognized they can in large measure be prevented1 and so the troubles which they engender overcome4 ,various organisms find in milk a congenial field for development4 ,yeasts and some fungi are capable of growth1 but more particularly the bacteria4 ,milk a suitable bacterial food4 ,the readiness with which milk undergoes fermentative changes indicates that it is well adapted to nourish bacterial life4 ,not only does it contain all the necessary nutritive substances but they are diluted in proper proportions so as to render them available for bacterial as well as mammalian life4 ,of the nitrogenous compounds1 the albumen is in readily assimilable form4 ,the casein1 being insoluble1 is not directly available1 until it is acted upon by proteid-dissolving enzyms like trypsin which may be secreted by bacteria4 ,the fat is relatively resistant to change1 although a few forms are capable of decomposing it4 ,milk sugar1 however1 is an admirable food for many species1 acids and sometimes gases being generally produced4 ,condition when secreted4 ,when examined under normal conditions milk always reveals bacterial life1 yet in the secreting cells of the udder of a healthy cow germ life is not found4 ,only when the gland is diseased are bacteria found in any abundance4 ,in the passage of the milk from the secreting cells to the outside it receives its first infection1 so that when drawn from the animal it generally contains a considerable number of organisms4 ,illustration3 ,,fig4 #e4 ,microscopic appearance of milk showing relative size of fat globules and bacteria4 ,contamination of milk4 ,from this time until it is consumed in one form or another1 it is continually subjected to contamination4 ,the major part of this infection occurs while the milk is on the farm and the degree of care which is exercised while the product is in the hands of the milk producer is the determining factor in the course of bacterial changes involved4 ,this of course does not exclude the possibility of contamination in the factory1 but usually milk is so thoroughly seeded by the time it reaches the factory that the infection which occurs here plays a relatively minor role to that which happens earlier4 ,the great majority of the organisms in milk are in no wise dangerous to health1 but many species are capable of producing various fermentative changes that injure the quality of the product for butter or cheese4 ,to be able to control abnormal changes of an undesirable character one must know the sources of infection which permit of the introduction of these unwelcome intruders4 ,sources of infection4 ,the bacterial life that finds its way into milk while it is yet on the farm may be traced to several sources1 which may be grouped under the following heads3 unclean dairy utensils1 fore milk1 coat of animal1 and general atmospheric surroundings4 ,the relative importance of these various factors fluctuates in each individual instance4 ,dairy utensils4 ,of first importance are the vessels that are used during milking1 and also all storage cans and other dairy utensils that come in contact with the milk after it is drawn4 ,by unclean utensils1 actually visible dirt need not always be considered1 although such material is often present in cracks and angles of pails and cans4 ,unless cleansed with especial care1 these are apt to be filled with foul and decomposing material that suffices to seed thoroughly the milk4 ,tin utensils are best4 ,where made with joints1 they should be well flushed with solder so as to be easily cleaned 7see ,fig4 #f74 ,in much of the cheaper tin ware on the market1 the soldering of joints and seams is very imperfect1 affording a place of refuge for bacteria and dirt4 ,cans are often used when they are in a condition wholly unsuitable for sanitary handling of milk4 ,when the tin coating becomes broken and the can is rusty1 the quality of the milk is often profoundly affected4 ,olson#a of the ,wisconsin ,station has shown that the action of rennet is greatly impaired where milk comes in contact with a rusty iron surface4 ,illustration3 ,,fig4 #f4 ,with the introduction of the form or hand separator a new milk utensil has been added to those previously in use and one which is very frequently not well cleaned4 ,where water is run through the machine to rinse out the milk particles1 gross bacterial contamination occurs and the use of the machine much increases the germ content of the milk4 ,every time the separator is used it should be taken apart and thoroughly cleaned and dried before reassembling4#b ,use of milk-cans for transporting factory by-products4 ,the general custom of using the milk-cans to carry back to the farm the factory by-products 7skim-milk or whey7 has much in it that is to be deprecated4 ,these by-products are generally rich in bacterial life1 more especially where the closest scrutiny is not given to the daily cleaning of the vats and tanks4 ,too frequently the cans are not cleaned immediately upon arrival at the farm1 so that the conditions are favorable for rapid fermentation4 ,many of the taints that bother factories are directly traceable to such a cause4 ,a few dirty patrons will thus seriously infect the whole supply4 ,the responsibility for this defect should1 however1 not be laid entirely upon the shoulders of the producer4 ,the factory operator should see that the refuse material does not accumulate in the waste vats from day to day and is not transformed into a more or less putrid mass4 ,a dirty whey tank is not an especially good object lesson to the patron to keep his cans clean4 ,it is possible that abnormal fermentations or even contagious diseases may thus be disseminated4 ,suppose there appears in a dairy an infectious milk trouble1 such as bitter milk4 ,this milk is taken to the factory and passes unnoticed into the general milk-supply4 ,the skim-milk from the separator is of course infected with the germ1 and if conditions favor its growth1 the whole lot soon becomes tainted4 ,if this waste product is returned to the different patrons in the same cans that are used for the fresh milk1 the probabilities are strongly in favor of some of the cans being contaminated and thus infecting the milk supply of the patrons4 ,if the organism is endowed with spores so that it can withstand unfavorable conditions1 this taint may be spread from patron to patron simply through the infection of the vessels that are used in the transportation of the by-products4 ,connell has reported just such a case in a ,canadian cheese factory where an outbreak of slimy milk was traced to infected whey vats4 ,typhoid fever among people1 foot and mouth disease and tuberculosis among stock are not infrequently spread in this way4 ,in ,denmark1 portions of ,germany and some states in ,america1 compulsory heating of factory by-products is practiced to eliminate this danger4#c ,pollution of cans from whey tanks4 ,the danger is greater in cheese factories than in creameries1 for whey usually represents a more advanced stage of fermentation than skim-milk4 ,the higher temperature at which it is drawn facilitates more rapid bacterial growth1 and the conditions under which it is stored in many factories contribute to the ease with which fermentative changes can go on in it4 ,often this by-product is stored in wooden cisterns or tanks1 situated below ground1 where it becomes impossible to clean them out thoroughly4 ,a custom that is almost universally followed in the ,swiss cheese factories1 here in this country1 as in ,switzerland1 is fully as reprehensible as any dairy custom could well be4 ,in ,fig4 #g the arrangement in vogue for the disposal of the whey is shown4 ,the hot whey is run out through the trough from the factory into the large trough that is placed over the row of barrels1 as seen in the foreground4 ,each patron thus has allotted to him in his individual barrel his portion of the whey1 which he is supposed to remove day by day4 ,no attempt is made to clean out these receptacles1 and the inevitable result is that they become filled with a foul1 malodorous liquid1 especially in summer4 ,when such material is taken home in the same set of cans that is used to bring the fresh milk 7twice a day as is the usual custom in ,swiss factories71 it is no wonder that this industry is seriously handicapped by gassy fermentations that injure materially the quality of the product4 ,not only is the above danger a very considerable one1 but the quality of the factory by-product for feeding purposes1 whether it is skim-milk or whey1 is impaired through the development of fermentative changes4 ,illustration3 ,,fig4 #g4 ,swiss cheese factory 7,wisconsin71 showing careless way in which whey is handled4 ,each patron's share is placed in a barrel1 from which it is removed by him4 ,no attempt is made to cleanse these receptacles4 ,improved methods of disposal of by-products4 ,the difficulties which attend the distribution of these factory by-products have led to different methods of solution4 ,one is to use another separate set of receptacles to carry back these products to the farm4 ,this method has been tried1 and while it is deemed impracticable by many to handle two sets of vessels1 yet some of the most progressive factories report excellent results where this method is in use4 ,large barrels could be used for this purpose to economize in wagon space4 ,another method that has met with wider acceptance1 especially in creameries1 is the custom of pasteurizing or scalding the skim-milk immediately after it is separated1 so that it is returned to the farmer in a hot condition4 ,in factories where the whole milk is pasteurized1 further treatment of the by-product is not necessary4 ,in most factories steam1 generally exhaust1 is used directly in the milk1 and experience has shown that such milk1 without any cooling1 will keep sweet for a considerable number of hours longer than the untreated product4 ,it is noteworthy that the most advanced and progressive factories are the ones that appreciate the value of this work1 and although it involves some time and expense1 experience has shown the utility of the process in that a better grade of milk is furnished by the patrons of factories which follow this practice4#d ,the exclusion of all danger of animal or human disease is also possible in this way4 ,cleaning dairy utensils4 ,the thorough cleaning of all dairy apparatus that in any way comes in contact with the milk is one of the most fundamental and important problems in dairying4 ,all such apparatus should be so constructed as to permit of easy cleaning4 ,tinware1 preferably of the pressed variety1 gives the best surface for this purpose and is best suited for the handling of milk4 ,milk vessels should never be allowed to become dry when dirty1 for dried particles of milk residue are extremely difficult to remove4 ,in cleaning dairy utensils they should first be rinsed in lukewarm instead of hot water1 so as to remove organic matter without coagulating the milk4 ,then wash thoroughly in hot water1 using a good washing powder4 ,the best washing powders possess considerable disinfecting action4#e ,strong alkalies should not be used4 ,after washing rinse thoroughly in clean hot water4 ,if steam is available1 as it always is in creameries1 cans and pails should be turned over jet for a few moments4 ,while a momentary exposure will not suffice to completely sterilize such a vessel1 yet many bacteria are killed in even a short exposure1 and the cans dry more thoroughly and quickly when heated by steam4 ,not only should the greatest care be paid to the condition of the cans and milk-pails1 but all dippers1 strainers1 and other utensils that come in contact with the milk must be kept equally clean4 ,cloth strainers1 unless attended to1 are objectionable1 for the fine mesh of the cloth retains so much moisture that they become a veritable hot-bed of bacterial life1 unless they are daily boiled or steamed4 ,the inability to thoroughly render vessels bacteria-free with the conveniences which are generally to be found on the farm has led in some cases to the custom of washing and sterilizing the milk cans at the factory4 ,germ content of milk utensils4 ,naturally the number of bacteria found in different milk utensils after they have received their regular cleaning will be subject to great fluctuations2 but1 nevertheless1 such determinations are of value as giving a scientific foundation for practical methods of improvement4 ,the following studies may serve to indicate the relative importance of the utensils as a factor in milk contamination4 ,two cans were taken1 one of which had been cleaned in the ordinary way1 while the other was sterilized by steaming4 ,before milking1 the udder was thoroughly cleaned and special precautions taken to avoid raising of dust2 the fore milk was rejected4 ,milk drawn into these two cans showed the following germ content3 ,no4 bacteria ,hours before per cc4 souring4 ,steamed pail #afe #bh-a_/b ,ordinary pail #dbfe #bc ,harrison#f has shown how great a variation is in the bacterial content in milk cans4 ,the utensils were rinsed with #ajj cc4 of sterile water and numerical determinations of this rinsing water made4 ,in poorly cleaned cans1 the average germ content was #ddb1jjj2 in cans washed in tepid water and then scalded--the best farm practice--#ed1jjj1 and in cans carefully washed and then steamed for five minutes1 #hhj4 ,another method used by the writer is to wash the utensil with #ajj cc4 sterile wash water1 using a sterile swab to remove dirt4 ,then repeat the process twice or more with fresh rinsing waters1 making plate cultures from each4 ,the following data were obtained from three such determinations3 ,no4 bacteria in different washings4 ,total ,no4 ,i4 ,,ii4 ,,iii4 bacteria4 #g1hjj1jjj #a1dej1jjj #di1jjj #i1bii1jjj #bhc1jjj #dc1djj #ce1jjj #cfa1djj #a1fhe1jjj #aje1jjj #fa1djj #a1hea1djj ,infection of milk in udder cavity4 ,a frequently neglected but considerable factor of infection is that which is attributable to the bacteria which are present in the udder and which are removed in large numbers during the milking process4 ,an examination of the fore milk1 i4 e41 the first few streams from each teat1 and that which is subsequently withdrawn1 generally reveals a very much larger number of organisms in the fore milk4#g ,not infrequently will this part of the milk when drawn under as careful conditions as possible1 contain several score thousand organisms per cc4 ,if successive bacterial determinations are made at different periods of the milking1 as shown in the following experiment1 a marked diminution is to be noted after the first portion of the milk is removed3 ,bacterial content at different periods of milking4 ,fore #bjjth #bjjjth #dcjjth #fejjth ,strippings4 milk4 cc4 cc4 cc4 cc4 ,expt4 #a #f1ejj #a1gjj #dge #bbj #ge #e ,expt4 #b #h1ajj #a1fej #djj #bdj #ej #aj ,by some observers it has been claimed that it is possible to secure absolutely sterile milk in the strippings but this is rarely so4 ,it is quite probable that such reported results are due to the fact that too small quantities of milk were used in the examinations and so erroneous conclusions were drawn4 ,this marked diminution in numbers indicates that the larger proportion of the organisms found in the fore milk are present in the lower portion of the udder and milk ducts4 ,when consideration is given to the structure of the udder1 it is readily apparent that infection will be greater here than above4 ,illustration3 ,,fig4 #h4 ,sectional view of udder showing teat with milk duct connecting exterior with the milk cistern4 ,milk sinuses are mostly shown in cross section interspersed and below the secreting tissue 7,moore and ,ward74 ,the udder is composed of secreting tissue 7gland cells7 held in place by fibrous connective tissue4 ,ramifying throughout this glandular structure are numerous channels 7milk sinuses7 that serve to convey the milk from the cells where it is produced into the milk cistern1 a common receptacle just above the teats4 ,this cavity is connected with the exterior through the milk duct in the teat1 which is more or less tightly closed by the circular sphincter muscles1 thus preventing the milk from flowing out4 ,the mucous membranes of the milk duct and cistern are naturally moist4 ,the habits of the animal render it impossible to prevent infection of the external opening at the end of the teat and there is no mechanical reason why bacteria cannot readily find their way along the moist lining membrane for some distance4 ,if organisms are adapted to this kind of an environment1 ideal conditions exist for their multiplication1 as moisture1 warmth and suitable food supply are present4 ,the question arises how far up into this organ is penetration possible8 ,within late years numerous observations have been made on the presence of organisms in the upper portion of the udder in contact with the secreting tissue4#h ,these investigations prove that bacteria are distributed throughout the whole of the udder1 although numerically they are much less abundant in the region of the milk-secreting tissue than in the lower portion4 ,ward's conclusions are that milk when secreted by the glands of a healthy udder is sterile4 ,it may however1 immediately become contaminated by the bacteria which are normally present in the smaller milk ducts of the udder4 ,nature of bacteria in fore milk4 ,generally speaking the number of different species found in the fore milk is not large1 and of those which do appear many occur at only occasional intervals4 ,moore#i in the examination of #i udders found #bj different forms1 and of these only #c species predominated1 all of which proved to be micrococci4 ,streptococci have also been quite frequently reported4 ,freudenreich#aj found the most common types to be cocci1 belonging to both the liquefying and non-liquefying class4 ,peptonizing#aa and spore-bearing#ab species have also been reported as well as gas-producing#ac forms allied to the colon bacillus4 ,such findings are1 however1 due in all probability to accidental invasion4 ,most investigators report the absence of the distinctively lactic-acid group of organisms4#ad ,origin of bacteria in udder4 ,there is no question but that many of the types of bacteria found in the udder gain access from the outside4 ,those belonging to the spore-bearing1 digesting and intestinal types have such a favorable opportunity for introduction from outside and are so unlikely to have come directly from the body of the animal1 that the external source of infection is much more probable4 ,whether this explanation answers the origin of the cocci that are so generally found in the upper portion of the udder is questionable4 ,the statement is ordinarily made that the inner tissues of healthy organs are bacteria-free1 but the studies of ,ford#ae seem to indicate that #gj per cent4 of such organs1 removed under aseptic conditions from guinea pigs1 rabbits1 dogs and cats contained living organisms4 ,others have reported similar results in which cocci have been found#af very similar to those occurring in the udder4 ,these findings increase the probability that the origin of this type is from the blood4 ,the persistence of certain species in the udder for months as noted by ,ward indicates possibility of growth of some forms at least4 ,stocking#ag has shown where cows are not milked clean that the germ content of succeeding milkings is greatly increased4 ,artificial introduction of bacteria into udder4 ,if bacteria are capable of actually developing in the udder proper1 it ought to be possible to easily demonstrate this by the artificial introduction of cultures4 ,in a number of cases#ah such experiments have been made with various saprophytic forms1 such as ,b4 prodigiosus1 lactic acid bacilli and others4 ,in no case has it appeared evident that actual growth has occurred1 although the introduced organism has been demonstrated in diminishing numbers for #e-f days4 ,even the common lactic acid germ and a yellow liquefying coccus isolated from the fore milk failed to persist for more than a few days when thus artificially introduced4 ,this failure to colonize is indeed curious and needs explanation4 ,is it due to unsuitable environmental conditions or attributable to the germicidal influence of the milk8 ,various body fluids are known to possess the property of destroying bacteria and it is claimed by ,fokker#ai that this same property was found in freshly drawn milk4 ,this peculiarity has also been investigated by ,freudenreich1#bj and ,hunziker#ba who find a similar property4 ,no material increase in germ content takes place in milk for several hours when chilled to #dj deg4-#gj deg4 ,f42 on the other hand an actual1 but usually not a marked decrease is observed for about #f hours4 ,this phenomenon varies with the milk of different cows4 ,nothing is known as to the cause of this apparent germicidal action4 ,the question is yet by no means satisfactorily settled1 although the facts on which the hypothesis is based are not in controversy4 ,if such a peculiarity belongs to milk1 it is not at all improbable that it may serve to keep down the germ content in the udder4 ,freudenreich#bb found that udders which were not examined for some time after death showed abundant growth1 which fact he attributed to the loss of this germicidal property4 ,the infection of the whole milk can be materially reduced by rejecting the fore milk1 but it is questionable whether such rejection is worth while1 except in the case of sanitary dairies where milk is produced with as low a germ content as possible4 ,the intrinsic loss in butter fat in the fore milk is inconsiderable as the first few streams contain only about one-fifth the normal fat content4 ,infection of milk after withdrawal from animal4 ,the germ content of the milk1 when it is being drawn from the animal is immediately increased upon contact with the atmosphere4 ,these organisms are derived from the surrounding air and the utensils in which the milk is received and stored4 ,the number of organisms which find their way into the milk depends largely upon the character of the surroundings4 ,bacteria are so intimately associated with dirt1 dust and filth of all kinds that wherever the latter are found1 the former are sure to be present in abundance4 ,the most important factors in the infection of the milk after withdrawal are the pollution which is directly traceable to the animal herself and the condition of the milk utensils4 ,fortunately both of these sources of contamination are capable of being greatly minimized by more careful methods of handling4 ,infection directly from the cow4 ,it is a popular belief that the organisms found in milk are derived from the feed and water which the cow consumes1 the same passing directly from the intestinal tract to the milk by the way of the blood circulation4 ,such a view has no foundation in fact as bacteria absorbed into the circulation are practically all destroyed in the tissues by the action of the body fluids and cells4#bc ,while organisms cannot pass readily from the intestine to the udder1 yet this must not be interpreted as indicating that no attention should be given to the bacterial character of the material consumed4 ,the water supply given should be pure and wholesome and no decomposed or spoiled food should be used4 ,the infection traceable directly to the cow is modified materially by the conditions under which the animal is kept and the character of the feed consumed4 ,the nature of the fecal matter is in part dependent upon the character of the food4 ,the more nitrogenous rations with which animals are now fed leads to the production of softer fecal discharges which is more likely to soil the coat of the animal unless care is taken4 ,the same is true with animals kept on pasture in comparison with those fed dry fodder4 ,stall-fed animals1 however1 are more likely to have their flanks fouled1 unless special attention is paid to the removal of the manure4 ,all dairy stalls should be provided with a manure drop which should be cleaned as frequently as circumstances will permit4 ,illustration3 ,,fig4 #i4 ,showing the bacterial contamination arising from hair4 ,these hairs were allowed to fall on a sterile gelatin surface4 ,the adherent bacteria developed readily in this medium1 and the number of bacteria thus introduced into the milk from these hairs can be estimated by the number of developing colonies4 ,the animal herself contributes materially to the quota of germ life finding its way into the milk through the dislodgment of dust and filth particles adhering to its hairy coat4 ,the nature of this coat is such as to favor the retention of these particles4 ,unless care is taken the flanks and udder become polluted with fecal matter1 which upon drying is displaced with every movement of the animal4 ,every hair or dirt particle so dislodged and finding its way into the milk-pail adds its quota of organisms to the liquid4 ,this can be readily demonstrated by placing cow's hairs collected with care on the moist surface of gelatin culture plates4 ,almost invariably1 bacteria will be found in considerable numbers adhering to such hairs as is indicated in ,fig4 #i4 ,dirt particles are even richer in germ life4 ,not only is there the dislodgment of hairs1 epithelial scales and masses of dirt and filth1 but during the milking process1 as at all other times1 every motion of the animal is accompanied by a shower of invisible particles more or less teeming with bacterial life4 ,the amount of actual impurities found in milk is often considerable and when it is remembered that about one-half of fresh manure dissolves in milk1#bd and thus does not appear as sediment1 the presence of this undissolved residue bespeaks filthy conditions as to milking4 ,from actual tests made1 it is computed that the city of ,berlin1 ,germany consumes about #cjj pounds of such dirt and filth daily4 ,renk has laid down the following rule with reference to this insoluble dirt3 ,if a sample of milk shows any evidence of impurity settling on a transparent bottom within two hours1 it should be regarded as too dirty for use4 ,while the number of organisms here introduced is at all times large1 the character of the species is of even greater import4 ,derived primarily from dirt and fecal matter1 it is no wonder that such forms are able to produce very undesirable fermentative changes4 ,influence of milker4 ,the condition of the milker is not to be ignored in determining all possible factors of infection1 for when clothed in the dust-laden garments that have been worn all day1 a favorable opportunity for direct contamination is possible4 ,the filthy practice of wetting the hands with milk just before milking is to be condemned4 ,the milker's hands should be washed immediately before milking in clean water and dried4 ,a pinch of vaseline on hands is sometimes used to obtain a firmer grasp and prevents the ready dislodgment of scales4#be ,it must also be borne in mind that the milker may spread disease through the milk4 ,in typhoid fever and diphtheria1 the germs often remain in the system for weeks and thus make infection possible4 ,stocking#bf has shown that the individual milker exerts a potent influence on the total germ content of milk1 even where the procedure is quite the same4 ,in sanitary dairies milkers are usually clad in white duck suits4 ,milking by machinery4 ,several mechanical devices have been invented for milking1 some of which have been tested bacteriologically as to their efficiency4 ,harrison#bg has examined the ,thistle machine but found a much higher germ content than with hand-drawn milk4 ,the recent introduction of the ,burrel-,lawrence-,kennedy machine has led to numerous tests in which very satisfactory results have been obtained4 ,if the rubber parts of the milker are thoroughly cleaned and kept in lime water solution1 they remain nearly sterile4 ,when milk is properly handled1 the germ content may be greatly reduced4 ,reduction in dirt and adherent bacteria4 ,no factor of contamination is so susceptible of improvement as that which relates to the reduction in filth and dirt which gains access during and immediately subsequent to the milking4 ,the care which is taken to keep the coat of the animal clean by grooming lessens very much the grosser portion of such contamination1 but with a dry1 hairy coat1 fine scales and dust particles must of necessity be dislodged4#bh ,ordinarily the patron thinks all evidence of such dirt is removed if the milk is strained1 but this process only lessens the difficulty2 it does not overcome it4 ,various methods are in use1 the effectiveness of which is subject to considerable variation4 ,some of these look to the elimination of the bacteria after they are once introduced into the milk2 others to the prevention of infection in the first place4 #a4 ,straining the milk4 ,most of the visible1 solid particles of filth1 such as hairs1 dirt particles1 etc41 can be removed by simple straining1 the time-honored process of purification4 ,as ordinarily carried out1 this process often contributes to instead of diminishing the germ life in milk4 ,the strainer cloths unless washed and thoroughly sterilized by boiling harbor multitudes of organisms from day to day and may thus actually add to the organisms present4 ,various methods have been suggested for this simple process1 but the most practical and efficient strainer is that made of fine wire gauze to which is added #c-d layers of cheese cloth1 the whole to set over the storage milk can4 #b4 ,filtration4 ,in ,europe especially1 the system of cleaning milk by filtration through sand1 gravel and other substances has been quite extensively used4 ,these filters are built in sections and the milk passes from below upward4 ,the filtering substance is washed in hot water immediately after use and then steamed and finally baked4 ,while it is possible to remove the solid impurities in this way1 the germ content cannot be greatly reduced4#bi ,cellulose filters have also been suggested#cj as an improvement over the sand filters4 ,methods of filtration of this character have not been used under commercial conditions here in this country4 #c4 ,clarification in separator4 ,within recent years the custom has grown of clarifying milk or removing the visible dirt by passing the milk through a centrifugal separator the cream and skim milk being remixed after separation4 ,this process naturally removes the solid impurities as dirt1 hairs1 epithelial scales and cells1 also some of the casein1 making what is known as centrifuge slime4 ,this conglomerate mass is incomparably rich in germ life and the natural inference would be that the bacterial content of the milk would be greatly reduced by this procedure4 ,eckles and ,barnes#ca noted a reduction of #cg to #ef per cent4 of the bacteria but others have failed to observe such reductions4#cb ,this condition is explained by the more thorough breaking up of the bacterial masses in the process1 thus apparently not reducing them in numbers4 ,it is somewhat surprising that in spite of the elimination of much organic matter and bacteria1 such clarified milk sours as rapidly as the untreated product4#cc ,the mechanical shock of separation ruptures the clusters of fat globules and so delays creaming and also lessens the consistency of cream derived from such milk4 ,this practical disadvantage together with the increased expense of the operation and the failure to materially enhance the keeping quality of the product outweigh the advantage which might come from removal of solid impurities which can be largely accomplished on the farm by efficient straining4 #d4 ,washing the udder4 ,if a surface is moist1 bacteria adherent to it cannot be dislodged by ordinary movements4 ,thus the air over snow-covered mountains or oceans is relatively devoid of germ life4 ,the method of moistening the udder is applied with success to the hairy coat of the animal thus subserving the double purpose of cleaning the animal and preventing in large measure the continual dislodgment of dust particles4 ,after these parts have been well carded to remove loose hairs and dirt particles1 the skin should be thoroughly moistened with clean water and then wiped4 ,it has been urged that this procedure lessens the yield of milk but ,eckles#cd concludes from experiments that when the animal becomes accustomed to this treatment1 no noticeable change in amount of milk or butter-fat is produced4 ,the effectiveness of this method in reducing the actual amount of dirt and filth introduced into the milk as well as the great diminution in germ life is shown by the instructive experiments of ,fraser#ce who found that the actual amount of dirt dislodged from udders of apparently clean animals during the milking process was three and one-half times as much as when the cow's udders were washed4 ,from udders visibly polluted one ounce of such filth was removed in #bge pounds of milk1 while from cows whose udders had been washed1 the same amount of dirt was distributed through #bd1jcj pounds4 ,fraser observed as a result of #dbj examinations that the average germ content of #d-;inch culture dishes under clean but unwashed udders was #egh1 while under washed animals it was reduced to #aib4 ,from numerous tests made in the writer's laboratory1 it is evident that the germ content of the milk in the pail is increased from #bj1jjj-dj1jjj bacteria per minute during the milking period4 ,by far the larger part of this pollution can be easily prevented by cleaning and dampening the udder4 #e4 ,diminishing exposed surface of pail4 ,the entrance of organisms into the milk can be greatly reduced by lessening the area of the milk pail directly exposed to the dust shower4 ,a number of so-called sanitary or hygienic milk pails have been devised for this purpose4 ,in one case the pail is smaller at the top than bottom1 but in most of them the common form is kept and the exposed area is lessened by means of a cover1 the milk being received through a narrower opening4 ,in some cases1 strainers are also interposed so as to remove more effectually the coarse particles4 ,it is necessary to have these covers and strainers constructed in such a way so they can be easily removed and cleaned4 ,illustration3 ,,fig4 #aj4 ,sanitary milk pails designed to diminish the introduction of hairs1 scales1 dirt1 etc41 into milk4 ,stocking tested one of these pails 7,a1 ,fig4 #aj7 and found that #fc per cent of the dirt and #bi per cent4 of the bacteria were prevented from passing into the milk4 ,eckles examined one in which the germ content was found to be #cbjj per cc4 as against #dcbjj per cc4 in a common open pail4 ,this milk did not sour until it was #fd hours old in the first case while in the latter it curdled in #dc hours4 ,air in barn4 ,the atmosphere of the barn where the milking is done may frequently contribute considerable infection4 ,germ life is incapable of development in the air1 but in a dried condition1 organisms may retain their vitality for long periods4 ,anything which contributes to the production of dust in the stable and aids in the stirring up of the same increases the number of organisms to be found in the air 7,fig4 #aa74 ,thus1 the feeding of dry fodder and the bedding of animals with straw adds greatly to the germ life floating in the air4 ,dust may vary much in its germ content depending upon its origin4 ,fraser found the dust from corn meal to contain only about one-sixth to one-eighth as much germ life as that from hay or bran4#cf ,in time most of these dust particles settle to the floor1 but where the herd is kept in the barn1 the constant movement of the animals keeps these particles more or less in motion4 ,much can be done by forethought to lessen the germ content of stables4 ,feeding dry feed should not be done until after milking4#cg ,in some of the better sanitary dairies1 it is customary to have a special milking room that is arranged with special reference to the elimination of all dust4 ,in this way this source of infection may be quite obviated as the air of a clean1 still room is relatively free from bacteria1 especially if the floor is moistened4 ,it has often been noted that the milk of stall-fed animals does not keep as well as that milked out of doors1 a condition in part attributable to the lessened contamination4 ,illustration3 ,,fig4 #aa4 ,effect of contaminated air4 ,the number of spots indicate the colonies that have developed from the bacteria which fell in #cj seconds on the surface of the gelatin plate 7#c inches in diameter74 ,this exposure was made at time the cows were fed4 ,relative importance of different sources of infection4 ,it is impossible to measure accurately the influence of the different sources of infection as these are continually subject to modification in each and every case4 ,as a general rule1 however1 where milk is drawn and handled without any special care1 the utensils and the animal contribute the larger proportion of dirt and bacteria that find their way into milk4 ,where the manner of milking and handling is designed to exclude the largest number of organisms possible1 the bacteria appearing in the fore milk make up the major portion remaining4 ,by putting into practice the various suggestions that have been made with reference to diminishing the bacterial content of milk1 it is possible to greatly reduce the number of organisms found therein1 and at the same time materially improve the keeping quality of the milk4 ,backhaus#ch estimates that the germ life in milk can be easily reduced to one-two thousandth of its original number by using care in milking4 ,he reports a series of experiments covering two years in which milk was secured that averaged less than #aj1jjj bacteria per cc41 while that secured under ordinary conditions averaged over #ejj1jjj4 ,illustration3 ,,fig4 #ab4 ,bacterial content of milk handled in ordinary way4 ,each spot represents a colony growing on gelatin plate4 ,compare with ,fig4 #ac1 where same quantity of milk is used in making culture4 ,over #ae1jjj bacteria per cc4 in this milk4 ,fig4 #ac gives an illustration as to what care in milking will do in the way of eliminating bacteria4 ,fig4 #ab shows a gelatin plate seeded with the same quantity of milk that was used in making the culture indicated by ,fig4 #ac4 ,the first plate was inoculated with milk drawn under good conditions1 the germ content of which was found to be #ae1ejj bacteria per cc41 while the sample secured under as nearly aseptic conditions as possible 7,fig4 #ac7 contained only #ccj organisms in the same volume4 ,illustration3 ,,fig4 #ac4 ,bacterial content of milk drawn with care4 ,diminished germ content is shown by smaller number of colonies 7#ccj bacteria per cc474 ,compare this culture with that shown in ,fig4 #ab4 ,sanitary or certified milk4 ,within recent years there has been more or less generally introduced into many cities1 the custom of supplying high grade milk that has been handled in a way so as to diminish its germ content as much as possible4 ,milk of this character is frequently known as sanitary1 hygienic or certified1 the last term being used in connection with a certification from veterinary authorities or boards of health as to the freedom of animals from contagious disease4 ,frequently a numerical bacterial standard is exacted as a pre-requisite to the recommendation of the board of examining physicians4 ,thus1 the ,pediatric ,society of ,philadelphia requires all children's milk that receives its recommendation to have not more than #aj1jjj bacteria per cc4 ,such a standard has its value in the scrupulous cleanliness that must prevail in order to secure these results4 ,this in itself is practically a guarantee of the absence of those bacteria liable to produce trouble in children4 ,the number of organisms found in such milks is surprisingly low when compared with ordinary milk4 ,naturally1 there is considerable fluctuation from day to day1 and occasionally the germ content is increased to a high figure without any apparent reason4 ,the average results though1 show a greatly reduced number of organisms4 ,de ,schweinitz#ci found in a ,washington dairy in #aac examinations extending throughout a year1 an average of #f1dhe bacteria per cc4 ,the daily analyses made of the ,walker-,gordon supply sold in ,philadelphia for an entire year1 showed that the milk almost always contained less than #e1jjj bacteria per cc4 and on #abj days out of the year the germ content was #a1jjj organisms per cc4 or less4 ,from a practical point of view1 the improvement in quality of sanitary milk1 in comparison with the ordinary product is seen in the enhanced keeping quality4 ,during the ,paris ,exposition in #aijj1 milk and cream from several such dairies in the ,united ,states were shipped to ,paris1 arriving in good condition after #ae to #ah days transit4 ,when milk has been handled in such a way1 it is evident that it is much better suited to serve as a food supply than where it has undergone the fermentative changes incident to the development of myriads of organisms4 ,application of foregoing precautions to all milk producers4 ,milk is so susceptible to bacterial changes that it is necessary to protect it from invasion1 if its original purity is to be maintained1 and yet1 from a practical point of view1 the use to which it is destined has much to do with the care necessary to take in handling4 ,the effect of the bacterial contamination of milk depends largely upon the way in which the product is used4 ,to the milk-man engaged in the distribution of milk for direct consumption1 all bacterial life is more or less of a detriment1 while to the butter-maker and cheese-maker some forms are a direct necessity4 ,it is unnecessary and impracticable to require the same degree of care in handling milk destined to be worked up into factory products as is done1 for instance1 in sanitary milk supplies1 but this fact should not be interpreted to mean that the care of milk for factories is a matter of small consequence4 ,in fact no more important dairy problem exists1 and the purer and better the quality of the raw material the better the product will be4 ,particularly is this true with reference to cheese-making4 ,dairymen have learned many lessons in the severe school of experience1 but it is earnestly to be hoped that future conditions will not be summed up in the words of the eminent ,german dairy scientist1 ,prof4 ,fleischmann1 when he says that all the results of scientific investigation which have found such great practical application in the treatment of disease1 in disinfection1 and in the preservation of various products1 are almost entirely ignored in milking4 ,growth of bacteria in milk4 ,milk is so well suited as a medium for the development of germ life that it might be expected that all microorganisms would develop rapidly therein1 and yet1 as a matter of fact1 growth does not begin at once1 even though the milk may be richly seeded4 ,at ordinary temperatures1 such as #gj deg4 ,f41 no appreciable increase is to be noted for a period of #f-i hours2 at lower temperatures 7#ed deg4 ,f47 this period is prolonged to #cj-dj hours or even longer4 ,after this period has elapsed1 active growth begins and continues more or less rapidly until after curdling4 ,the cause of this suspended development is attributed to the germicidal properties inherent to the milk4#dj ,milk is of course seeded with a considerable variety of organisms at first4 ,the liquefying and inert species are the most abundant1 the distinctively lactic acid class occurring sparsely1 if at all4 ,as milk increases in age1 germ growth begins to occur4 ,more or less development of all types go on1 but soon the lactic species gain the ascendency1 owing to their being better suited to this environment2 they soon outstrip all other species1 with the result that normal curdling generally supervenes4 ,the growth of this type is largely conditioned by the presence of the milk sugar4 ,if the sugar is removed from milk by dialysis1 the liquid undergoes putrefactive changes due to the fact that the putrefactive bacteria are able to grow if no acid is produced4 ,relation of temperature to growth4 ,when growth does once begin in milk1 the temperature at which it is stored exerts the most profound effect on the rate of development4 ,when milk is not artificially cooled1 it retains its heat for some hours1 and consequently the conditions become very favorable for the rapid multiplication of the contained organisms1 as is shown in following results obtained by ,freudenreich#da3 ,no4 of bacteria per cc4 in milk kept at different temperatures4 #gg deg4 ,f4 #ie deg4 ,f4 #e hrs4 after milking #aj1jjj #cj1jjj #h #be1jjj #ab1jjj1jjj #ab #df1jjj #ce1bhj1jjj #bf #e1gjj1jjj #ej1jjj1jjj ,illustration3 ,,fig4 #ad4 ,effect of cooling milk on the growth of bacteria4 ,conn#db is inclined to regard temperature of more significance in determining the keeping quality than the original infection of the milk itself4 ,milk which curdled in #ah hours at #ih deg4 ,f41 did not curdle in #dh hours at #gj deg41 and often did not change in two weeks1 if the temperature was kept at #ej deg4 ,f4 ,where kept for a considerable period at this low temperature1 the milk becomes filled with bacteria of the undesirable putrefactive type1 the lactic group being unable to form acid in any appreciable amounts4 ,running well water can be used for cooling1 if it is possible to secure it at a temperature of #dh deg4-#ej deg4 ,f4 ,the use of ice1 of course1 gives better results1 and in summer is greatly to be desired4 ,the influence of these lowered temperatures makes it possible to ship milk long distances#dc by rail for city supplies1 if the temperature is kept low during transit4 ,mixing night and morning milk4 ,not infrequently it happens when old milk is mixed with new1 that the course of the fermentative changes is more rapid than would have been the case if the two milks had been kept apart4 ,thus1 adding the cooled night milk to the warm morning milk sometimes produces more rapid changes in both4 ,the explanation for this often imperfectly understood phenomenon is that germ growth may have gone on in the cooled milk1 and when this material is added to the warmer1 but bacteria-poor1 fresh milk1 the temperature of the whole mass is raised to a point suitable for the more rapid growth of all bacteria than would have occurred if the older milk had been kept chilled4 ,number of bacteria in milk4 ,the number of organisms found in milk depends upon 7#a7 the original amount of contamination1 7#b7 the age of the milk1 and 7#c7 the temperature at which it has been held4 ,these factors all fluctuate greatly in different cases2 consequently1 the germ life is subject to exceedingly wide variations4 ,here in ,america1 milk reaches the consumer with less bacteria than in ,europe1 although it may often be older4 ,this is due largely to the more wide-spread use of ice for chilling the milk en route to market4 ,examinations have been made of various supplies with the following results3 ,sedgwick and ,batchelder found in #eg tests of ,boston milk from #cj1jjj-d1bbj1jjj per cc4 ,jordan and ,heineman found #cj of samples of ,chicago milk to range from #ajj1jjj to #a1jjj1jjj while nearly one half were from #a-bj1jjj1jjj per cc4 ,the germ content of city milks increase rapidly in the summer months4 ,park#dd found #bej1jjj organisms per cc4 in winter1 about #a1jjj1jjj in cool weather and #e1jjj1jjj per cc4 in hot summer weather4 ,knox and ,bassett in ,baltimore report #a1ejj1jjj in spring and nearly #d1ejj1jjj in summer4 ,eckles#de studied milk under factory conditions4 ,he finds from #a1jjj1jjj to #e1jjj1jjj per cc4 in winter1 and in summer from #ae-cj millions4 ,bacterial standards for city supplies4 ,it would be very desirable to have a hygienic standard for city milk supplies1 as there is a butter fat and milk-solid test1 but the wide spread variation in germ content and the impracticability of utilizing ordinary bacterial determinations 7on account of time required7 makes the selection of such a standard difficult4 ,some hold1 as ,park1 that such a standard is feasible4 ,the ,new ,york ,city ,milk commission has set a standard of #cj1jjj bacteria per cc4 for their certified milk and #ajj1jjj per cc4 for inspected milk4 ,rochester1 ,n4 ,y4 has attempted the enforcement of such a standard 7limit1 #ajj1jjj per cc47 with good results it is claimed while ,boston has placed the legal limit at #ejj1jjj per cc4 ,quantitative standards would seem more applicable to certified or sanitary supplies than to general city supplies1 where the wide range in conditions lead to such enormous variations that the bacterial standard seems too refined a method for practical routine inspection4 ,other tests4 ,any test to be of much service must be capable of being quickly applied4 ,the writer believes for city milk inspectors that the acid test would serve a very useful purpose4 ,this test measures the acidity of the milk4 ,there is1 of course1 no close and direct relationship between the development of acidity and the growth of bacteria1 yet in a general way one follows the other at normal temperatures4 ,where the temperature is kept rather low1 bacterial growth might go on without much acid development1 but in the great majority of cases a high degree of acidity means either old milk1 in which there has been a long period of incubation1 or high temperature1 where rapid bacterial growth has been possible4 ,either of these conditions encourages germ growth and thus impairs the quality of the milk4 ,the rapid determination of acidity may be made in an approximate manner so as to serve as a test at the weigh-can or intake4 ,the test is best made by the use of the well known alkaline tablet which is composed of a solid alkali1 and the indicator1 phenolphthalein4 ,the tablets are dissolved in water1 one to each ounce used4 ,a number of white cups are filled with the proper quantity of the solution necessary to neutralize say1 #j4b per cent4 lactic acid4 ,then1 as the milk is delivered1 the proper quantity is taken from each can to which is added the tablet solution4 ,a retention of the pink color shows that there is not sufficient acid in the milk to neutralize the alkali used2 a disappearance of color indicates an excess of acid4 ,the standard selected is of course arbitrarily chosen4 ,in our experience1 #j4b per cent4 acidity 7figured as lactic71 has proven a satisfactory point4 ,with carefully handled milk the acidity ought to be reduced to about #j4ae per cent4 ,the acidity of the milk may be abnormally reduced if milk is kept in rusty cans1 owing to action of acid on the metal4 ,illustration3 ,,fig4 #ae4 ,apparatus used in making rapid acid test4 ,a definite quantity of the alkali solution and indicator is placed in the white tea cup4 ,to this is added the quantity of milk by means of the cartridge measure which would just be neutralized if the acidity was #j4b per cent4 ,a retention of the pink color shows a low acid milk2 its disappearance1 a high acid milk4 ,kinds of bacteria in milk4 ,the number of bacteria in milk is not of so much consequence as the kinds present4 ,with reference to the number of different species1 the more dirt and foreign matter the milk contains1 the larger the number of varieties found in the same4 ,while milk may contain forms that are injurious to man1 still the great majority of them have no apparent effect on human health4 ,in their effect on milk1 the case is much different4 ,depending upon their action in milk1 they may be grouped into three classes3 #a4 ,inert group1 those producing no visible change in the milk4 #b4 ,sour milk forms1 those breaking up the milk sugar with or without the formation of gas4 #c4 ,digesting or peptonizing group1 those capable of rendering the casein of milk soluble and more or less completely digested4 ,a surprisingly large number of bacteria that are found in milk belong to the first class4 ,undoubtedly they affect the chemical characteristics of the milk somewhat1 but not to the extent that it becomes physically perceptible4 ,eckles#df reports in a creamery supply from #bj to #ee per cent4 of entire flora as included in this class4 ,by far the most important group is that embraced under the second head4 ,it includes not only the true lactic acid types in which no gas is formed1 but those species capable of producing gases and various kinds of acids4 ,these organisms are the distinctively milk bacteria1 although they do not predominate when the milk is first drawn4 ,their adaptation to this medium is normally shown1 however1 by this extremely rapid growth1 in which they soon gain the ascendency over all other species present4 ,it is to this lactic acid class that the favorable flavor-producing organisms belong which are concerned in butter-making4 ,they are also indispensable in cheese-making4 ,the third class represents those capable of producing a liquefied or digested condition on gelatin or in milk4 ,they are usually the spore-bearing species which gain access from filth and dirt4 ,their high powers of resistance due to spores makes it difficult to eradicate this type1 although they are materially held in subjection by the lactic bacteria4 ,the number of different kinds that have been found in milk is quite considerable1 something over #bjj species having been described more or less thoroughly4 ,in all probability1 however1 many of these forms will be found to be identical when they are subjected to a more critical study4 ,direct absorption of taints4 ,a tainted condition in milk may result from the development of bacteria1 acting upon various constituents of the milk1 and transforming these in such a way as to produce by-products that impair the flavor or appearance of the liquid2 or it may be produced by the milk being brought in contact with any odoriferous or aromatic substance1 under conditions that permit of the direct absorption of such odors4 ,this latter class of taints is entirely independent of bacterial action1 and is largely attributable to the physical property which milk possesses of being able to absorb volatile odors1 the fat in particular1 having a great affinity for many of these substances4 ,this direct absorption may occur before the milk is withdrawn from the animal1 or afterwards if exposed to strong odors4 ,it is not uncommon for the milk of animals advanced in lactation to have a more or less strongly marked odor and taste2 sometimes this is apt to be bitter1 at other times salty to the taste4 ,it is a defect that is peculiar to individual animals and is liable to recur at approximately the same period in lactation4 ,the peculiar cowy or animal odor of fresh milk is an inherent peculiarity that is due to the direct absorption of volatile elements from the animal herself4 ,this condition is very much exaggerated when the animal consumes strong-flavored substances as garlic1 leeks1 turnips and cabbage4 ,the volatile substances that give to these vegetables their characteristic odor are quickly diffused through the system1 and if such foods are consumed some few hours before milking1 the odor in the milk will be most pronounced4 ,the intensity of such taints is diminished greatly and often wholly disappears1 if the milking is not done for some hours 7#h-ab7 after such foods are consumed4 ,this same principle applies in lesser degree to many green fodders that are more suitable as feed for animals1 as silage1 green rye1 rape1 etc4 ,not infrequently1 such fodders as these produce so strong a taint in milk as to render it useless for human use4 ,troubles from such sources could be entirely obviated by feeding limited quantities of such material immediately after milking4 ,under such conditions the taint produced is usually eliminated before the next milking4 ,the milk of swill-fed cows is said to possess a peculiar taste1 and the urine of animals fed on this food is said to be abnormally acid4 ,brewers' grains and distillery slops when fed in excess also induce a similar condition in the milk4 ,milk may also acquire other than volatile substances directly from the animal1 as in cases where drugs1 as belladonna1 castor oil1 sulfur1 turpentine1 jalap1 croton oil1 and many others have been used as medicine4 ,such mineral poisons as arsenic have been known to appear eight hours after ingestion1 and persist for a period of three weeks before being eliminated4 ,absorption of odors after milking4 ,if milk is brought in contact with strong odors after being drawn from the animal1 it will absorb them readily1 as in the barn1 where frequently it is exposed to the odor of manure and other fermenting organic matter4 ,it has long been a popular belief that milk evolves odors and cannot absorb them so long as it is warmer than the surrounding air1 but from experimental evidence1 the writer#dg has definitely shown that the direct absorption of odors takes place much more rapidly when the milk is warm than when cold1 although under either condition1 it absorbs volatile substances with considerable avidity4 ,in this test fresh milk was exposed to an atmosphere impregnated with odors of various essential oils and other odor-bearing substances4 ,under these conditions1 the cooler milk was tainted very much less than the milk at body temperature even where the period of exposure was brief4 ,it is therefore evident that an exposure in the cow barn where the volatile emanations from the animals themselves and their excreta taint the air will often result in the absorption of these odors by the milk to such an extent as to seriously affect the flavor4 ,the custom of straining the milk in the barn has long been deprecated as inconsistent with proper dairy practice1 and in the light of the above experiments1 an additional reason is evident why this should not be done4 ,even after milk is thoroughly cooled1 it may absorb odors as seen where the same is stored in a refrigerator with certain fruits1 meats1 fish1 etc4 ,distinguishing bacterial from non-bacterial taints4 ,in perfectly fresh milk1 it is relatively easy to distinguish between taints caused by the growth of bacteria and those attributable to direct absorption4 ,if the taint is evident at time of milking1 it is in all probability due to character of feed consumed1 or possibly to medicines4 ,if1 however1 the intensity of the taint grows more pronounced as the milk becomes older1 then it is probably due to living organisms1 which require a certain period of incubation before their fermentative properties are most evident4 ,moreover1 if the difficulty is of bacterial origin1 it can be frequently transferred to another lot of milk 7heated or sterilized is preferable7 by inoculating same with some of the original milk4 ,not all abnormal fermentations are able though to compete with the lactic acid bacteria1 and hence outbreaks of this sort soon die out by the re-establishment of more normal conditions4 ,treatment of directly absorbed taints4 ,much can be done to overcome taints of this nature by exercising greater care in regard to the feed of animals1 and especially as to the time of feeding and milking4 ,but with milk already tainted1 it is often possible to materially improve its condition4 ,thorough aeration has been frequently recommended1 but most satisfactory results have been obtained where a combined process of aeration and pasteurization was resorted to4 ,where the milk is used in making butter1 the difficulty has been successfully met by washing the cream with twice its volume of hot water in which a little saltpeter has been dissolved 7one teaspoonful per gallon71 and then separating it again4#dh ,the treatment of abnormal conditions due to bacteria has been given already under the respective sources of infection1 and is also still further amplified in following chapter4 ,aeration4 ,it is a common belief that aeration is of great aid in improving the quality of milk1 yet1 when closely studied1 no material improvement can be determined1 either where the milk is made into butter or sold as milk4 ,dean in ,canada and ,storch in ,denmark have both experimented on the influence of aeration in butter making1 but with negative results4 ,marshall and ,doane failed to observe any material improvement in keeping quality1 but it is true that odors are eliminated from the milk during aeration4 ,the infection of the milk during aeration often more than counterbalances the reputed advantage4 ,especially is this so if the aeration is carried out in an atmosphere that is not perfectly clean and pure4 ,in practice aeration differs greatly4 ,in some cases1 air is forced into the milk2 in others1 the milk is allowed to distribute itself in a thin sheet over a broad surface and fall some distance so that it is brought intimately in contact with the air4 ,this latter process is certainly much more effective if carried out under conditions which preclude infection4 ,it must be remembered that aeration is frequently combined with cooling1 in which case the reputed advantages may not be entirely attributable to the process of aeration4 ,infection of milk in the factory4 ,the problem of proper handling of milk is not entirely solved when the milk is delivered to the factory or creamery1 although it might be said that the danger of infection is much greater while the milk is on the farm4 ,in the factory1 infection can be minimized because effective measures of cleanliness can be more easily applied4 ,steam is available in most cases1 so that all vats1 cans1 churns and pails can be thoroughly scalded4 ,special emphasis should be given to the matter of cleaning pumps and pipes4 ,the difficulty of keeping these utensils clean often leads to neglect and subsequent infection4 ,in ,swiss cheese factories1 the custom of using home-made rennet solutions is responsible for considerable factory infection4 ,natural rennets are soaked in whey which is kept warm in order to extract the rennet ferment4 ,this solution when used for curdling the milk often adds undesirable yeasts and other gas-generating organisms1 which are later the cause of abnormal ferment action in the cheese 7,see page #ahf74 ,the influence of the air on the germ content of the milk is1 as a rule1 overestimated4 ,if the air is quiet1 and free from dust1 the amount of germ life in the same is not relatively large4 ,in a creamery or factory1 infection from this source ought to be much reduced1 for the reason that the floors and wall are1 as a rule1 quite damp1 and hence germ life cannot easily be dislodged4 ,the majority of organisms found under such conditions come from the person of the operators and attendants4 ,any infection can easily be prevented by having the ripening cream-vats covered with a canvas cloth4 ,the clothing of the operator should be different from the ordinary wearing-apparel4 ,if made of white duck1 the presence of dirt is more quickly recognized1 and greater care will therefore be taken than if ordinary clothes are worn4 ,the surroundings of the factory have much to do with the danger of germ infection4 ,many factories are poorly constructed and the drainage is poor1 so that filth and slime collect about and especially under the factory4 ,the emanations from these give the peculiar factory odor that indicates fermenting matter4 ,not only are these odors absorbed directly1 but germ life from the same is apt to find its way into the milk4 ,connell#di has recently reported a serious defect in cheese that was traced to germ infection from defective factory drains4 ,the water supply of a factory is also a question of prime importance4 ,when taken from a shallow well1 especially if surface drainage from the factory is possible1 the water may be contaminated to such an extent as to introduce undesirable bacteria in such numbers that the normal course of fermentation may be changed4 ,the quality of the water1 aside from flavor1 can be best determined by making a curd test 7p4 #gf7 which is done by adding some of the water to boiled milk and incubating the same4 ,if gassy fermentations occur1 it signifies an abnormal condition4 ,in deep wells1 pumped as thoroughly as is generally the case with factory wells1 the germ content should be very low1 ranging from a few score to a few hundred bacteria per cc4 at most4 ,harrison#ej has recently traced an off-flavor in cheese in a ,canadian factory to an infection arising from the water-supply4 ,he found the same germ in both water and cheese and by inoculating a culture into pasteurized milk succeeded in producing the undesirable flavor4 ,the danger from ice is much less1 for the reason that good dairy practice does not sanction using ice directly in contact with milk or cream4 ,then1 too1 ice is largely purified in the process of freezing1 although if secured from a polluted source1 reliance should not be placed in the method of purification2 for even freezing does not destroy all vegetating bacteria4 ,,footnotes3 #a ,olson4 #bd ,rept4 ,wis4 ,expt4 ,stat41 #aijg4 #b ,erf and ,melick ,bull4 #aca1 ,kan4 ,expt4 ,stat41 ,apr4 #aije4 #c ,storch 7#dj ,rept4 ,danish ,expt4 ,stat41 ,copenhagen1 #ahih7 has devised a test whereby it can be determined whether this treatment has been carried out or not3 ,milk contains a soluble enzym known as galactase which has the property of decomposing hydrogen peroxid4 ,if milk is heated to #agf deg4 ,f4 7#hj deg4 ,c47 or above1 this enzym is destroyed so that the above reaction no longer takes place4 ,if potassium iodid and starch are added to unheated milk and the same treated with hydrogen peroxid1 the decomposition of the latter agent releases oxygen which acts on the potassium salt1 which in turn gives off free iodine that turns the starch blue4 #d ,mc,kay1 ,n4 ,y4 ,prod4 ,rev41 ,mch4 #bb1 #ahii4 #e ,doane1 ,bull4 #gi1 ,md4 ,expt4 ,stat41 ,jan4 #aijb4 #f ,harrison1 #bb ,rept4 ,ont4 ,agr'l ,coll41 #ahif1 p4 #aac4 #g ,moore and ,ward1 ,bull4 #aeh1 ,cornell ,expt4 ,stat41 ,jan4 #ahii2 ,ward1 ,bull4 #agh1 ,cornell ,expt4 ,stat41 ,jan4 #aijj4 #h ,harrison1 #bb ,rept4 ,ont4 ,agr4 ,coll41 #ahif1 p4 #ajh2 ,moore1 #ab ,rept4 ,bur4 ,animal ,ind41 ,u4 ,s4 ,dept4 ,ag41 #ahie-f1 p4 #bfa4 #i ,moore1 ,bacteria in ,milk1 ,n4 ,y4 ,dept4 ,ag41 #aijb4 #aj ,freudenreich1 ,cent4 f4 ,bakt41 ,,ii ,abt41 #aj3 #dah1 #aijc4 #aa ,harrison1 #bb ,rept4 ,ont4 ,agr4 ,coll41 #ahif1 p4 #ajh4 #ab ,marshall1 ,bull4 #adg1 ,mich4 ,expt4 ,stat41 p4 #db4 #ac ,moore and ,ward1 ,bull4 #aeh1 ,cornell ,expt4 ,stat41 ,jan4 #ahii4 #ad ,burr1 ,r4 ,h4 ,cent4 f4 ,bakt41 ,,ii ,abt41 #h3 #bcf1 #aijb4 ,freudenreich1 l4 c4 p4 #dah4 ,ward1 ,bull4 #agh1 ,cornell ,expt4 ,stat41 p4 #bgg4 ,bolley 7,cent4 f4 ,bakt41 ,,ii ,abt41 #a3 #gie1 #ahie71 in #cj experiments found #ab out of #af species to belong to lactic class4 ,harrison 7,trans4 ,can4 ,inst41 #g3 #dgd1 #aijb-c7 records the lactic type as most commonly present4 #ae ,ford1 ,journ4 of ,hyg41 #aija1 #a3 #bgg4 #af ,freudenreich1 l4 c4 p4 #dba4 #ag ,stocking1 ,bull4 #db1 ,storrs ,expt4 ,stat41 ,june1 #aijf4 #ah ,dinwiddie1 ,bull1 #de ,ark4 ,expt4 ,stat41 p4 #eg4 ,ward1 ,journ4 ,appld4 ,mic4 #a3 #bje1 #ahih4 ,appel1 ,milch ,zeit41 ,no4 #ag1 #aijj4 ,harrison and ,cumming1 ,journ4 ,appld4 ,mic4 #e3 #bjhg4 ,russell and ,hastings1 #ba ,rept4 ,wis4 ,expt4 ,stat41 #aeh1 #aijd4 #ai ,fokker1 ,zeit4 f4 ,hyg41 #i3 #da1 #ahij4 #bj ,freudenreich1 ,ann4 de ,microg41 #c3 #aah1 #ahia4 #ba ,hunziker1 ,bull4 #aig1 ,cornell ,expt4 ,stat41 ,dec4 #aija4 #bb ,freudenreich1 ,cent4 f4 ,bakt41 ,,ii ,abt41 #aj3 #dag1 #aijc4 #bc ,this general statement is in the main correct1 although ,ford 7,journ4 of ,hyg41 #a3 #bgg1 #aija7 claims to have found organisms sparingly present in healthy tissues4 #bd ,backhaus1 ,milch ,zeit41 #bf3 #ceg1 #ahig4 #be ,freudenreich1 ,die ,bakteriologie1 p4 #cj4 #bf ,stocking1 ,bull4 #db1 ,storrs ,expt4 ,stat41 ,june #aijf4 #bg ,harrison1 ,cent4 f4 ,bakt41 ,,ii ,abt41 #e3 #ahc1 #ahii4 #bh ,drysdale1 ,trans4 ,high4 and ,agr4 ,soc4 ,scotland4 #e ,series1 #aj3 #aff1 #ahih4 #bi ,schuppan1 7,cent4 f4 ,bakt41 #ac3 #aee1 #ahic7 claims to have found a reduction of #dh per cent4 in the ,copenhagen filters while in the more extended work of ,dunbar and ,kister 7,milch ,zeit41 pp4 #gec1 #ghg1 #ahii7 the bacterial content was higher in the filtered milk in #ag cases out of #bb4 #cj ,backhaus and ,cronheim1 ,journ4 f4 ,landw41 #de3 #bbb1 #ahig4 #ca ,eckles and ,barnes1 ,bull4 #aei ,iowa ,expt4 ,stat41 ,aug4 #aija4 #cb ,dunbar and ,kister1 ,milch ,zeit41 p4 #gec1 #ahii4 ,harrison and ,streit1 ,trans4 ,can4 ,inst41 #g3 #dhh1 #aijb-c4 #cc ,doane1 ,bull4 #hh ,md4 ,expt4 ,stat41 ,may #aijc4 #cd ,eckles1 ,hoard's ,dairyman1 ,july #h1 #ahih4 #ce ,fraser1 ,bull4 #ia1 ,ill4 ,expt4 ,stat4 #cf ,fraser1 ,bull4 #ia1 ,ill4 ,expt4 ,stat41 ,dec4 #aijc4 #cg ,stocking1 ,bull4 #db1 ,storrs ,expt4 ,stat41 ,june1 #aijf4 #ch ,backhaus4 ,ber4 ,landw4 ,inst4 ,univ4 ,koenigsberg #b3 #ab1 #ahig4 #ci ,de ,schweinitz1 ,nat4 ,med4 ,rev41 ,april1 #ahii4 #dj ,conn1 ,proc4 ,soc4 ,amer4 ,bacteriologists1 #aijb4 #da ,freudenreich1 ,ann4 de ,microg41 #b3aae1 #ahij4 #db ,conn1 ,bull4 #bf1 ,storrs ,expt4 ,stat4 #dc ,new ,york ,city is supplied with milk that is shipped #cej miles4 #dd ,park1 ,n4 ,y4 ,univ4 ,bull41 #a3 #he1 #aija4 #de ,eckles1 ,bull4 #ei1 ,iowa ,expt4 ,stat41 ,aug4 #aija4 #df ,eckles1 ,bull4 #ei1 ,iowa ,expt4 ,stat41 ,aug4 #aija4 #dg ,russell1 #ae ,rept4 ,wis4 ,expt4 ,stat4 #ahih1 p4 #ajd4 #dh ,alvord1 ,circ4 ,no4 #i1 ,u4 ,s4 ,dept4 ,agric4 7,div4 of ,bot474 #di ,connell1 ,rept4 of ,commissioner of ,agr41 ,canada1 #ahig1 part ,,xvi1 p4 #ae4 #ej ,harrison1 ,hoard's ,dairyman1 ,march #d1 #ahih4 ,,chapter ,,iv4 ,,fermentations ,,in ,,milk ,,and ,,their ,,treatment4 ,under the conditions in which milk is drawn1 it is practically impossible to secure the same without bacterial contamination4 ,the result of the introduction of these organisms often changes its character materially as most bacteria cause the production of more or less pronounced fermentative processes4 ,under normal conditions1 milk sours1 i4 e41 develops lactic acid1 but at times this more common fermentation may be replaced by other changes which are marked by the production of some other more or less undesirable flavor1 odor or change in appearance4 ,in referring to these changes1 it is usually customary to designate them after the most prominent by-product formed1 but it must be kept in mind that generally some other decomposition products are usually produced4 ,whether the organisms producing this or that series of changes prevail or not depends upon the initial seeding1 and the conditions under which the milk is kept4 ,ordinarily1 the lactic acid organisms grow so luxuriantly in the milk that they overpower all competitors and so determine the nature of the fermentation2 but occasionally the milk becomes infected with other types of bacteria in relatively large numbers and the conditions may be especially suitable to the development of these forms1 thereby modifying the course of the normal changes that occur4 ,the kinds of bacteria that find it possible to develop in milk may be included under two heads3 #a4 ,those which cause no appreciable change in the milk1 either in taste1 odor or appearance4 ,while these are frequently designated as the inert bacteria1 it must not be supposed that they have absolutely no effect on milk4 ,it is probably true in most cases that slight changes of a chemical nature are produced1 but the nature of the changes do not permit of ready recognition4 #b4 ,this class embraces all those organisms which1 as a result of their growth1 are capable of producing evident changes4 ,these transformations may be such as to affect the taste1 as in the sour milk or in the bitter fermentations1 or the odor1 as in some of the fetid changes1 or the appearance of the milk1 as in the slimy and color changes later described4 ,souring of milk4 ,ordinarily if milk is allowed to stand for several days at ordinary temperatures it turns sour4 ,this is due to the formation of lactic acid1 which is produced by the decomposition of the milk-sugar4 ,while this change is well nigh universal1 it does not occur without a pre-existing cause1 and that is the presence of certain living bacterial forms4 ,these organisms develop in milk with great rapidity1 and the decomposition changes that are noted in souring are due to the by-products of their development4 ,the milk-sugar undergoes fermentation1 the chief product being lactic acid1 although various other by-products1 as other organic acids 7acetic1 formic and succinic71 different alcohols and gaseous products1 as ,,co#b1 ,h1 ,n and methane 7,,ch#d7 are produced in small amounts4 ,in this fermentation1 the acidity begins to be evident to the taste when it reaches about #j4c per cent41 calculated as lactic acid4 ,as the formation of acid goes on1 the casein is precipitated and incipient curdling or lobbering of the milk occurs4 ,this begins to be apparent when the acidity is about #j4d per cent41 but the curd becomes more solid with increasing acidity4 ,the rapidity of curdling is also dependent upon the temperature of the milk4 ,thus milk which at ordinary temperatures might remain fluid often curdles when heated4 ,the growth of the bacteria is continued until about #j4h to #a4j per cent4 acid is formed1 although the maximum amount fluctuates considerably with different lactic acid species4 ,further formation then ceases even though all of the milk-sugar is not used up1 because of the inability of the lactic bacteria to continue their growth in such acid solutions4 ,as this acidity is really in the milk serum1 cream never develops so much acid as milk1 because a larger proportion of its volume is made up of butter-fat globules4 ,this fact must be considered in the ripening of cream in butter-making where the per cent4 of fat is subject to wide fluctuations4 ,the formation of lactic acid is a characteristic that is possessed by a large number of bacteria1 micrococci as well as bacilli being numerously represented4 ,still the preponderance of evidence is in favor of the view that a few types are responsible for most of these changes4 ,the most common type found in spontaneously soured milk changes the milk-sugar into lactic acid without the production of any gas4 ,this type has been described by various workers on ,european as well as ,american milks1 and is designated by ,conn as the ,bact4 lactis acidi type4#ea ,it is subject to considerable variation under different conditions4 ,curiously enough if milk which has been drawn with special care is examined immediately after milking1 the lactic organisms are not usually found4 ,they are incapable of development in the udder itself1 as shown by injections into the milk cistern4 ,they abound1 however1 on hay1 in dust1 in the barn air1 on the hairy coat of the animal1 and from these sources easily gain access to the milk4 ,in this medium they find an exceptionally favorable environment and soon begin a very rapid growth1 so that by the time milk is consumed1 either in the form of milk or milk products1 they make up numerically the larger portion of the bacteria present4 ,another widely disseminated1 although numerically less prevalent1 type is ,b4 lactis aerogenes4 ,this type forms gas in milk so that the soured milk is torn by the presence of gas bubbles4 ,it also grows more luxuriantly in contact with the air4 ,other types occur more or less sporadically1 some of which are capable of liquefying the casein of milk while at the same time they also develop lactic acid4 ,conn and ,aikman refer to the fact that over one hundred species capable of producing variable quantities of lactic acid are already known4 ,it is fair to presume1 however1 that a careful comparative study of these would show that simply racial differences exist in many cases1 and therefore1 that they are not distinct species4 ,as a group these bacteria are characterized by their inability to liquefy gelatin or develop spores4 ,on account of this latter characteristic they are easily destroyed when milk is pasteurized4 ,they live under aerobic or anaerobic conditions1 many of them being able to grow in either environment1 although1 according to ,mc,donnell1#eb they are more virulent when air is not excluded4 ,while growth of these lactic forms may go on in milk throughout a relatively wide range in temperature1 appreciable quantities of acid are not produced except very slowly at temperatures below #ej deg4 ,f4#ec ,from the standpoint of frequency the most common abnormal changes that occur in milk are those in which gases of varying character are developed in connection with acids1 from the milk sugar4 ,other volatile products imparting bad flavors usually accompany gas production4 ,these fermentations are of most serious import in the cheese industry1 as they are especially prone to develop in the manufacture of milk into certain types of cheese4 ,not often is their development so rapid that they appear in the milk while it is yet in the hands of the milk producer1 but almost invariably the introduction of the causal organisms takes place while the milk is on the farm4 ,numerous varieties of bacteria possess this property of producing gas 7,h and ,,co#b are most common although ,n and methane 7,,ch#d7 are sometimes produced74 ,the more common forms are those represented by ,b4 lactis aerogenes and the common fecal type1 ,b4 coli commune4 ,the ordinary habitat of this type is dirt and intestinal filth4 ,hence careless methods of milk handling invite this type of abnormal change in milk4 ,it is a wide-spread belief that thunder storms cause milk to sour prematurely1 but this idea has no scientific foundation4 ,experiments#ed with the electric spark1 ozone and loud detonations show no effect on acid development1 but the atmospheric conditions usually incident to a thunder storm are such as permit of a more rapid growth of organisms4 ,there is no reason to believe but that the phenomenon of souring is wholly related to the development of bacteria4 ,sterile milks are never affected by the action of electric storms4 ,gassy milks4 ,where these gas bacteria abound1 the amount of lactic acid is generally reduced1 due to the splitting up of some of the sugar into gaseous products4 ,this type of germ life does not seem to be able to develop well in the presence of the typical lactic acid non gas-forming bacteria4 ,illustration3 ,,fig4 #af4 ,cheese made from gassy milk4 ,sweet curdling and digesting fermentations4 ,not infrequently milk1 instead of undergoing spontaneous souring1 curdles in a weakly acid or neutral condition1 in which state it is said to have undergone sweet curdling4 ,the coagulation of the milk is caused by the action of enzyms of a rennet type that are formed by the growth of various species of bacteria4 ,later the whey separates more or less perfectly from the curd1 producing a wheyed off condition4 ,generally the coagulum in these cases is soft and somewhat slimy4 ,the curd usually diminishes in bulk1 due to the gradual digestion or peptonization of the casein by proteid-dissolving enzyms 7tryptic type7 that are also produced by the bacteria causing the change4 ,a large number of bacteria possess the property of affecting milk in this way4 ,so far as known they are able to liquefy gelatin 7also a peptonizing process7 and form spores4 ,the ,tyrothrix type of bacteria 7so named by ,duclaux on account of the supposed relation to cheese ripening7 belongs to this class4 ,the hay and potato forms are also digesters4 ,organisms of this type are generally associated with filth and manure1 and find their way into the milk from the accumulations on the coat of the animal4 ,conn#ee has separated the rennet enzym from bacterial cultures in a relatively pure condition1 while ,fermi#ef has isolated the digestive ferment from several species4 ,duclaux#eg has given to this digesting enzym the name casease or cheese ferment4 ,these isolated ferments when added to fresh milk possess the power of causing the characteristic curdling and subsequent digestion quite independent of cell development4 ,the quantity of ferment produced by different species differs materially in some cases4 ,in these digestive fermentations1 the chemical transformations are profound1 the complex proteid molecule being broken down into albumoses1 peptones1 amido-acids 7tyrosin and leucin7 and ammonia as well as fatty acids4 ,not infrequently these fermentations gain the ascendency over the normal souring change1 but under ordinary conditions they are held in abeyance1 although this type of bacteria is always present to some extent in milk4 ,when the lactic acid bacteria are destroyed1 as in boiled1 sterilized or pasteurized milk1 these rennet-producing1 digesting species develop4 ,butyric acid fermentations4 ,the formation of butyric acid in milk which may be recognized by the rancid butter odor is not infrequently seen in old1 sour milk1 and for a long time was thought to be a continuation of the lactic fermentation1 but it is now believed that these organisms find more favorable conditions for growth1 not so much on account of the lactic acid formed as in the absence of dissolved oxygen in the milk which is consumed by the sour-milk organisms4 ,most of the butyric class of bacteria are spore-bearing1 and hence they are frequently present in boiled or sterilized milk4 ,the by-products formed in this series of changes are quite numerous4 ,in most cases1 butyric acid is prominent1 but in addition to this1 other organic acids1 as lactic1 succinic1 and acetic1 are produced1 likewise different alcohols4 ,concerning the chemical origin of butyric acid there is yet some doubt4 ,duclaux#eh affirms that the fat1 sugar and casein are all decomposed by various forms4 ,in some cases1 the reaction of the milk is alkaline1 with other species it may be neutral or acid4 ,this type of fermentation has not received the study it deserves4 ,in milk these organisms are not of great importance1 as this fermentation does not readily gain the ascendency over the lactic bacteria4 ,ropy or slimy milk4 ,the viscosity of milk is often markedly increased over that which it normally possesses4 ,the intensity of this abnormal condition may vary much2 in some cases the milk becoming viscous or slimy2 in others stringing out into long threads1 several feet in length1 as in ,fig4 #ag4 ,two sets of conditions are responsible for these ropy or slimy milks4 ,the most common is where the milk is clotted or stringy when drawn1 as in some forms of garget4 ,this is generally due to the presence of viscid pus1 and is often accompanied by a bloody discharge1 such a condition representing an inflamed state of the udder4 ,ropiness of this character is not usually communicable from one lot of milk to another4 ,illustration3 ,,fig4 #ag4 ,ropy milk4 ,the communicable form of ropy milk only appears after the milk has been drawn from the udder for a day or so1 and is caused by the development of various species of bacteria which find their way into the milk after it is drawn4 ,these defects are liable to occur at any season of the year4 ,their presence in a dairy is a source of much trouble1 as the unsightly appearance of the milk precludes its use as food1 although there is no evidence that these ropy fermentations are dangerous to health4 ,there are undoubtedly a number of different species of bacteria that are capable of producing these viscid changes1#ei but it is quite probable that they are not of equal importance in infecting milk under natural conditions4 ,in the majority of cases studied in this country1#fj the causal organism seems to be ,b4 lactis viscosus1 a form first found by ,adametz in surface waters4#fa ,this organism possesses the property of developing at low temperatures 7#de deg4-#ej deg4 ,f471 and consequently it is often able in winter to supplant the lactic-acid forms4 ,ward has found this germ repeatedly in water tanks where milk cans are cooled2 and under these conditions it is easy to see how infection of the milk might occur4 ,marshall#fb reports an outbreak which he traced to an external infection of the udder2 in another case1 the slime-forming organism was abundant in the barn dust4 ,a defect of this character is often perpetuated in a dairy for some time1 and may therefore become exceedingly troublesome4 ,in one instance in the writer's experience1 a milk dealer lost over #aej a month for several months from ropy cream4 ,failure to properly sterilize cans1 and particularly strainer cloths1 is frequently responsible for a continuance of trouble of this sort4 ,the slimy substance formed in milk comes from various constituents of the milk1 and the chemical character of the slime produced also varies with different germs4 ,in some cases the slimy material is merely the swollen outer cell membrane of the bacteria themselves as in the case of ,b4 lactis viscosus2 in others it is due to the decomposition of the proteids1 but often the chief decomposition product appears to come from a viscous fermentation of the milk-sugar4 ,an interesting case of a fermentation of this class being utilized in dairying is seen in the use of lange wei 7long or stringy whey7 which is employed as a starter in ,holland to control the gassy fermentations in ,edam cheese4 ,this slimy change is due to the growth of ,streptococcus ,hollandicus4#fc ,alcoholic fermentations4 ,although glucose or cane-sugar solutions are extremely prone to undergo alcoholic fermentation1 milk sugar does not readily undergo this change4 ,where such changes are produced it is due to yeasts4 ,several outbreaks attributable to such a cause have been reported4#fd ,russell and ,hastings#fe have found these milk-sugar splitting yeasts particularly abundant in regions where ,swiss cheese is made1 a condition made possible by the use of whey-soaked rennets in making such cheese4 ,kephir and ,koumiss are liquors much used in the ,orient which are made from milk that has undergone alcoholic fermentation4 ,koumiss was originally made from mare's milk but is now often made from cows' milk by adding cane sugar and yeast4 ,in addition to the ,,co#b developed1 alcohol1 lactic acid1 and casein-dissolving ferments are formed4 ,kephir is made by adding to milk ,kephir grains1 which are a mass of yeast and bacterial cells4 ,the yeasts produce alcohol and ,,co#b while the bacteria change the casein of milk1 rendering it more digestible4 ,these beverages are frequently recommended to persons who seem to be unable to digest raw milk readily4 ,the exact nature of the changes produced are not yet well understood4#ff ,bitter milk4 ,the presence of bitter substances in milk may be ascribed to a variety of causes4 ,a number of plants1 such as lupines1 ragweed and chicory1 possess the property of affecting milk when the same are consumed by animals4 ,at certain stages in lactation1 a bitter salty taste is occasionally to be noted that is peculiar to individual animals4 ,a considerable number of cases of bitter milk have1 however1 been traced to bacterial origin4 ,for a number of years the bitter fermentation of milk was thought to be associated with the butyric fermentation1 but ,weigmann#fg showed that the two conditions were not dependent upon each other4 ,he found that the organism which produced the bitter taste acted upon the casein4 ,conn#fh observed a coccus form in bitter cream that was able to impart a bitter flavor to milk4 ,sometimes a bitter condition does not develop in the milk1 but may appear later in the milk products1 as in the case of a micrococcus which ,freudenreich#fi found in cheese4 ,harrison#gj has traced a common bitter condition in ,canadian milk to a milk-sugar splitting yeast1 ,torula amara which not only grows rapidly in milk but produces an undesirable bitterness in cheddar cheese4 ,cream ripened at low temperatures not infrequently develops a bitter flavor1 showing that the optimum temperature for this type of fermentation is below the typical lactic acid change4 ,milk that has been heated often develops a bitter condition4 ,the explanation of this is that the bacteria producing the bitter substances usually possess endospores1 and that while the boiling or sterilizing of milk easily kills the lactic acid germs1 these forms on account of their greater resisting powers are not destroyed by the heat4 ,soapy milk3 ,a soapy flavor in milk was traced by ,weigmann and ,zirn#ga to a specific bacillus1 ,b4 lactis saponacei1 that they found gained access to the milk in one case from the bedding and in another instance from hay4 ,a similar outbreak has been reported in this country1#gb due to a germ acting on the casein and albumen4 ,red milk4 ,the most common trouble of this nature in milk is due to presence of blood1 which is most frequently caused by some wound in the udder4 ,the ingestion of certain plants as sedges and scouring rushes is also said to cause a bloody condition2 madders impart a reddish tinge due to coloring matter absorbed4 ,defects of this class can be readily distinguished from those due to germ growth because they are apparent at time of milking4 ,where blood is actually present1 the corpuscles settle out in a short time if left undisturbed4 ,there are a number of chromogenic or color-producing bacteria that are able to grow in milk1 but their action is so slow that generally they are not of much consequence4 ,moreover their development is usually confined to the surface of the milk as it stands in a vessel4 ,the most important is the well-known ,b4 prodigiosus4 ,another form found at times in milk possessing low acidity#gc is ,b4 lactis erythrogenes4 ,this species only develops the red color in the dark4 ,in the light1 it forms a yellow pigment4 ,various other organisms have been reported at different times4#gd ,blue milk4 ,blue milk has been known for many years1 its communicable nature being established as long ago as #ahch4 ,it appears on the surface of milk first as isolated particles of bluish or grey color1 which later become confluent1 the blue color increasing in intensity as the acidity increases4 ,the causal organism1 ,b4 cyanogenes1 is very resistant toward drying1#ge thus accounting for its persistence4 ,in ,mecklenberg an outbreak of this sort once continued for several years4 ,it has frequently been observed in ,europe in the past1 but is not now so often reported4 ,occasional outbreaks have been reported in this country4 ,other kinds of colored milk4 ,two or three chromogenic forms producing still other colors have occasionally been found in milk4 ,adametz#gf discovered in a sample of cooked milk a peculiar form 7,bacillus synxanthus7 that produced a citron-yellow appearance which precipitated and finally rendered soluble the casein4 ,adametz1 ,conn1 and ,list have described other species that confer tints of yellow on milk4 ,some of these are bright lemon1 others orange1 and some amber in color4 ,still other color-producing bacteria1 such as those that produce violet or green changes in the milk1 have been observed4 ,in fact1 almost any of the chromogenic bacteria are able to produce their color changes in milk as it is such an excellent food medium4 ,under ordinary conditions1 these do not gain access to milk in sufficient numbers so that they modify the appearance of it except in occasional instances4 ,treatment of abnormal fermentations4 ,if the taint is recognized as of bacterial origin 7see p4 #eg7 and is found in the mixed milk of the herd1 it is necessary to ascertain1 first1 whether it is a general trouble1 or restricted to one or more animals4 ,this can sometimes be done by separating the milk of the different cows and noting whether any abnormal condition develops in the respective samples4 ,fermentation tests4 ,the most satisfactory way to detect the presence of the taints more often present is to make a fermentation test of one kind or another4 ,these tests are most frequently used at the factory1 to enable the maker to detect the presence of milk that is likely to prove unfit for use1 especially in cheese making4 ,they are based upon the principle that if milk is held at a moderately high temperature1 the bacteria will develop rapidly4 ,a number of different methods have been devised for this purpose4 ,in ,walther's lacto-fermentator samples of milk are simply allowed to stand in bottles or glass jars until they sour4 ,they are examined at intervals of several hours4 ,if the curdled milk is homogeneous and has a pure acid smell1 the milk is regarded as all right4 ,if it floats in a turbid serum1 is full of gas or ragged holes1 it is abnormal4 ,as generally carried out1 no attempt is made to have these vessels sterile4 ,gerber's test is a similar test that has been extensively employed in ,switzerland4 ,sometimes a few drops of rennet are added to the milk so as to curdle the same1 and thus permit of the more ready detection of the gas that is evolved4 ,wisconsin curd test4 ,the method of testing milk described below was devised at the ,wisconsin ,experiment ,station in #ahie by ,babcock1 ,russell and ,decker4#gg ,it was used first in connection with experimental work on the influence of gas-generating bacteria in cheese making1 but its applicability to the detection of all taints in milk produced by bacteria makes it a valuable test for abnormal fermentations in general4 ,in the curd test a small pat of curd is made in a glass jar from each sample of milk4 ,these tests may be made in any receptacle that has been cleaned in boiling water1 and to keep the temperature more nearly uniform these jars should be immersed in warm water1 as in a wash tub or some other receptacle4 ,when the milk is about #ie deg4 ,f41 about ten drops of rennet extract are added to each sample and mixed thoroughly with the milk4 ,the jars should then remain undisturbed until the milk is completely curdled2 then the curd is cut into small pieces with a case knife and stirred to expel the whey4 ,the whey should be poured off at frequent intervals until the curd mats4 ,if the sample be kept at blood heat 7#ih deg4 ,f47 for six to eight hours1 it will be ready to examine4 ,illustration3 ,,fig4 #ah4 ,improved bottles for making curd test4 ,a1 test bottle complete2 ,b1 bottle showing construction of cover2 ,s1 sieve to hold back the curd when bottle is inverted2 ,c1 outer cover with 7,d ,h7 drain holes to permit of removal of whey4 ,more convenient types of this test than the improvised apparatus just alluded to have been devised by different dairy manufacturers4 ,generally1 they consist of a special bottle having a full-sized top1 thus permitting the easy removal of the curd4 ,the one shown in ,fig4 #ah is provided with a sieve of such construction that the bottles will drain thoroughly if inclined in an inverted position4 ,interpretation of results of test4 ,the curd from a good milk has a firm1 solid texture1 and should contain at most only a few small pin holes4 ,it may have some large1 irregular1 mechanical holes where the curd particles have failed to cement1 as is seen in ,fig4 #ai4 ,if gas-producing bacteria are very prevalent in the milk1 the conditions under which the test is made cause such a rapid growth of the same that the evidence of the abnormal fermentation may be readily seen in the spongy texture of the curd 7,fig4 #bj74 ,if the undesirable organisms are not very abundant and the conditions not especially suited to their growth1 the pin holes will be less frequent4 ,illustration3 ,,fig4 #ai4 ,curd from a good milk4 ,the large irregular holes are mechanical4 ,sometimes the curds show no evidence of gas1 but their abnormal condition can be recognized by the mushy texture and the presence of off flavors that are rendered more apparent by keeping them in closed bottles4 ,this condition is abnormal and is apt to produce quite as serious results as if gas was formed4 ,overcoming taints by use of starters4 ,another method of combatting abnormal fermentations that is often fruitful1 is that which rests upon the inability of one kind of bacteria to grow in the same medium in competition with certain other species4 ,some of the undesirable taints in factories can be controlled in large part by the introduction of starters made from certain organisms that are able to obtain the ascendency over the taint-producing germ4 ,such a method is commonly followed when a lactic ferment1 either a commercial pure culture1 or a home-made starter1 is added to milk to overcome the effect of gas-generating bacteria4 ,illustration3 ,,fig4 #bj4 ,curd from a badly tainted milk4 ,large ragged holes are mechanical2 numerous small holes due to gas4 ,this curd was a floater4 ,a similar illustration is seen in the case of the lange wei 7slimy whey71 that is used in the manufacture of ,edam cheese to control the character of the fermentation of the milk4 ,this same method is sometimes applied in dealing with certain abnormal fermentations that are apt to occur on the farm4 ,it is particularly useful with those tainted milks known as sweet curdling4 ,the ferment organisms concerned in this change are unable to develop in the presence of lactic acid bacteria1 so the addition of a clean sour milk as a starter restores the normal conditions by giving the ordinary milk bacteria the ascendency4 ,chemical disinfection4 ,in exceptional instances it may be necessary to employ chemical disinfectants to restore the normal conditions4 ,of course with such diseases as tuberculosis1 very stringent measures are required1 as they are such a direct menace to human life1 but with these abnormal or taint-producing fermentations1 care and cleanliness1 well directed1 will usually overcome the trouble4 ,if it becomes necessary to employ chemical substances as disinfecting agents1 their use should always be preceded by a thorough cleansing with hot water so that the germicide may come in direct contact with the surface to be disinfected4 ,it must be borne in mind that many chemicals act as deodorants1 i4e41 destroy the offensive odor1 without destroying the cause of the trouble4 ,sulfur is often recommended as a disinfecting agent1 but its use should be carefully controlled1 otherwise the vapors have but little germicidal power4 ,the common practice of burning a small quantity in a room or any closed space for a few moments has little or no effect upon germ life4 ,the effect of sulfur vapor 7,,so#b7 alone upon germ life is relatively slight1 but if this gas is produced in the presence of moisture1 sulfurous acid 7,h#b,,so#c7 is formed1 which is much more efficient4 ,to use this agent effectively1 it must be burned in large quantities in a moist atmosphere 7three lbs4 to every #a1jjj cubic feet of space71 for at least twelve hours4 ,after this operation1 the space should be thoroughly aired4 ,formalin1 a watery solution of a gas known as formaldehyde1 is a new disinfectant that recent experience has demonstrated to be very useful4 ,it may be used as a gas where rooms are to be disinfected1 or applied as a liquid where desired4 ,it is much more powerful in its action than sulfur1 and it has a great advantage over mercury and other strong disinfectants1 as it is not so poisonous to man as it is to the lower forms of life4 ,bleaching powder or chloride of lime is often recommended where a chemical can be advantageously used4 ,this substance is a good disinfectant as well as a deodorant1 and if applied as a wash1 in the proportion of four to six ounces of the powder to one gallon of water1 it will destroy most forms of life4 ,in many cases this agent is inapplicable on account of its odor4 ,corrosive sublimate 7,hg,cl#b7 for most purposes is a good disinfectant1 but it is such an intense poison that its use is dangerous in places that are at all accessible to stock4 ,for the disinfection of walls in stables and barns1 common thin white wash ,ca7,,oh7#b is admirably adapted if made from freshly-burned quick lime4 ,it possesses strong germicidal powers1 increases the amount of light in the barn1 is a good absorbent of odors1 and is exceedingly cheap4 ,carbolic acid1 creosote1 and such products1 while excellent disinfectants1 cannot well be used on account of their odor1 especially in factories4 ,for gutters1 drains1 and waste pipes in factories1 vitriol salts 7sulfates of copper1 iron and zinc7 are sometimes used4 ,these are deodorants as well as disinfectants1 and are not so objectionable to use on account of their odor4 ,these suggestions as to the use of chemicals1 however1 only apply to extreme cases and should not be brought into requisition until a thorough application of hot water1 soap1 a little soda1 and the scrubbing brush have failed to do their work4 ,,footnotes3 #ea ,guenther and ,thierfelder1 ,arch4 f4 ,hyg41 #be3afd1 #ahie2 ,leichmann1 ,cent4 f4 ,bakt41 #b3bha1 #ahif2 ,esten1 #i ,rept4 ,storrs ,expt4 ,stat41 p4 #dd1 #ahif2 ,dinwiddie1 ,bull4 #de1 ,ark4 ,expt4 ,stat41 ,may1 #ahig2 ,kozai1 ,zeit4 f4 ,hyg41 #ch3chf1 #aija2 ,weigmann1 ,hyg4 ,milk ,congress1 ,hamburg1 #aijc1 p4 #cge4 #eb ,mc,donnell1 ,inaug4 ,diss41 ,kiel4 #ahii1 p4 #ci4 #ec ,kayser1 ,cent4 f4 ,bakt4 ,,ii4 ,abt4 #a3dcf4 #ed ,treadwell1 ,science1 #ahid1 #ag3agh4 #ee ,conn1 #e ,rept4 ,storrs ,expt4 ,stat41 #ahib1 p4 #cif4 #ef ,fermi1 ,arch4 f4 ,hyg41 #ahib1 #ad3a4 #eg ,duclaux1 ,le ,lait1 p4 #aba4 #eh ,duclaux1 ,principes de ,laiterie1 p4 #fg4 #ei ,guillebeau 7,milch ,zeit41 #ahib1 p4 #hjh7 has studied over a dozen different forms that possess this property4 #fj ,ward1 ,bull4 #afe1 ,cornell ,expt4 ,stat41 ,mch41 #ahii2 also ,bull4 #aie1 ,ibid41 ,nov41 #aija4 #fa ,adametz1 ,landw4 ,jahr41 #ahia1 p4 #ahe4 #fb ,marshall1 ,mich4 ,expt4 ,stat41 ,bull4 #adj4 #fc ,milch ,zeit41 #ahii1 p4 #ihb4 #fd ,duclaux1 ,principes de ,laiterie1 p4 #fj4 ,heinze and ,cohn1 ,zeit4 f4 ,hyg41 #df3 #bhf1 #aijd4 #fe ,bull4 #abh1 ,wis4 ,expt4 ,stat41 ,sept4 #aije4 #ff ,freudenreich1 ,landw4 ,jahr4 d4 ,schweiz1 #ahif1 #aj2 #a4 #fg ,weigmann1 ,milch ,zeit41 #ahij1 p4 #hha4 #fh ,conn1 #c ,rept4 ,storrs ,expt4 ,stat41 #ahij1 p4 #aeh4 #fi ,freudenreich1 ,fuehl4 ,landw4 ,ztg4 #dc3 #cfa4 #gj ,harrison1 ,bull4 #abj ,ont4 ,agr'l4 ,coll41 ,may1 #aijb4 #ga ,milch ,zeit4 #bb3efi4 #gb ,marshall1 ,bull4 #adf1 ,mich4 ,expt4 ,stat41 p4 #af4 #gc ,grotenfelt1 ,milch ,zeit41 #ahhi1 p4 #bfc4 #gd ,menge1 ,cent4 f4 ,bakt41 #f3eif2 ,keferstein1 ,cent4 f4 ,bakt41 #ba3agg4 #ge ,heim1 ,arb4 a4 d4 ,kais4 ,gesundheitsamte1 #e3egh4 #gf ,adametz1 ,milch ,zeit41 #ahij1 p4 #bbe4 #gg #ab ,rept4 ,wis4 ,expt4 ,stat41 #ahie1 p4 #adh2 also ,bull4 #fg1 ,ibid41 ,june1 #ahih4 ,,chapter ,v4 ,,relation ,,of ,,disease-,,bacteria ,,to ,,milk4 ,practical experience with epidemic disease has abundantly demonstrated the fact that milk not infrequently serves as a vehicle for the dissemination of contagion4 ,attention has been prominently called to this relation by ,ernest ,hart1#gh who in #ahhj compiled statistical evidence showing the numerous outbreaks of various contagious diseases that had been associated with milk infection up to that time4 ,since then1 further compilations have been made by ,freeman1#gi and also by ,busey and ,kober1#hj who have collected the data with reference to outbreaks from #ahhj to #ahii4 ,these statistics indicate the relative importance of milk as a factor in the dissemination of disease4 ,the danger from this source is much intensified for the reason that milk1 generally speaking1 is consumed in a raw state2 and also because a considerable number of disease-producing bacteria are able1 not merely to exist1 but actually thrive and grow in milk1 even though the normal milk bacteria are also present4 ,moreover the recognition of the presence of such pathogenic forms is complicated by the fact that often they do not alter the appearance of the milk sufficiently so that their presence can be detected by a physical examination4 ,these facts which have been experimentally determined1 coupled with the numerous clinical cases on record1 make a strong case against milk serving as an agent in the dissemination of disease4 ,origin of pathogenic bacteria in milk4 ,disease-producing bacteria may be grouped with reference to their relation toward milk into two classes1 depending upon the manner in which infection occurs3 ,class ,i4 ,disease-producing bacteria capable of being transmitted directly from a diseased animal to man through the medium of infected milk4 ,class ,,ii4 ,bacteria pathogenic for man but not for cattle which are capable of thriving in milk after it is drawn from the animal4 ,in the first group the disease produced by the specific organism must be common to both cattle and man4 ,the organism must live a parasitic life in the animal1 developing in the udder1 and so infect the milk supply4 ,it may1 of course1 happen that diseases toward which domestic animals alone are susceptible may be spread from one animal to another in this way without affecting human beings4 ,in the second group1 the bacterial species lives a saprophytic existence1 growing in milk1 if it happens to find its way therein4 ,in such cases milk indirectly serves as an agent in the dissemination of disease1 by giving conditions favorable to the growth of the disease germ4 ,by far the most important of diseases that may be transmitted directly from animal to man through a diseased milk supply is tuberculosis1 but in addition to this1 foot and mouth disease 7aphthous fever in children71 anthrax and acute enteric troubles have also been traced to a similar source of infection4 ,the most important specific diseases that have been disseminated through subsequent pollution of the milk are typhoid fever1 diphtheria1 scarlet fever and cholera1 but1 of course1 the possibility exists that any disease germ capable of living and thriving in milk may be spread in this way4 ,in addition to these diseases that are caused by the introduction of specific organisms 7the causal organism of scarlet fever has not yet been definitely determined71 there are a large number of more or less illy-defined troubles of an intestinal character that occur especially in infants and young children that are undoubtedly attributable to the activity of microorganisms that gain access to milk during and subsequent to the milking1 and which produce changes in milk before or after its ingestion that result in the formation of toxic products4 ,,diseases ,,transmissible ,,from ,,animal ,,to ,,man ,,through ,,diseased ,,milk4 ,tuberculosis4 ,in view of the wide-spread distribution of this disease in both the human and the bovine race1 the relation of the same to milk supplies is a question of great importance4 ,it is now generally admitted that the different types of tubercular disease found in different kinds of animals and man are attributable to the development of the same organism1 ,bacillus tuberculosis1 although there are varieties of this organism found in different species of animals that are sufficiently distinct to permit of recognition4 ,the question of prime importance is1 whether the bovine type is transmissible to the human or not4 ,artificial inoculation of cattle with tuberculous human sputum as well as pure cultures of this variety show that the human type is able to make but slight headway in cattle4 ,this would indicate that the danger of cattle acquiring the infection from man would in all probability be very slight1 but these experiments offer no answer as to the possibility of transmission from the bovine to the human4 ,manifestly it is impossible to solve this problem by direct experiment upon man except by artificial inoculation1 but comparative experiments upon animals throw some light on the question4 ,theo4 ,smith#ha and others#hb have made parallel experiments with animals such as guinea pigs1 rabbits and pigeons1 inoculated with both bovine and human cultures of this organism4 ,the results obtained in the case of all animals tested show that the virulence of the two types was much different1 but that the bovine cultures were much more severe4 ,while of course this does not prove that transmission from bovine to human is possible1 still the importance of the fact must not be overlooked4 ,in a number of cases record of accidental infection from cattle to man has been noted4#hc ,these have occurred with persons engaged in making post-mortem examinations on tuberculous animals1 and the tubercular nature of the wound was proven in some cases by excision and inoculation4 ,in addition to data of this sort that is practically experimental in character1 there are also strong clinical reasons for considering that infection of human beings may occur through the medium of milk4 ,naturally such infection should produce intestinal tuberculosis1 and it is noteworthy that this phase of the disease is quite common in children especially between the ages of two and five4#hd ,it is difficult to determine1 though1 whether primary infection occurred through the intestine1 for1 usually1 other organs also become involved4 ,in a considerable number of cases in which tubercular infection by the most common channel1 inhalation1 seems to be excluded1 the evidence is strong that the disease was contracted through the medium of the milk1 but it is always very difficult to exclude the possibility of pulmonary infection4 ,tuberculosis as a bovine disease has increased rapidly during recent decades throughout many portions of the world4 ,this has been most marked in dairy regions4 ,its extremely insidious nature does not permit of an early recognition by physical means1 and it was not until the introduction of the tuberculin test#he in #ahib1 as a diagnostic aid that accurate knowledge of its distribution was possible4 ,the quite general introduction of this test in many regions has revealed an alarmingly large percentage of animals as affected4 ,in ,denmark in #ahid over forty per cent were diagnosed as tubercular4 ,in some parts of ,germany almost as bad a condition has been revealed4 ,slaughter-house statistics also show that the disease has increased rapidly since #ahij4 ,in this country the disease on the average is much less than in ,europe and is also very irregularly distributed4 ,in herds where it gained a foothold some years ago1 often the majority of animals are frequently infected2 many herds1 in fact the great majority1 are wholly free from all taint4 ,the disease has undoubtedly been most frequently introduced through the purchase of apparently healthy but incipiently affected animals4 ,consequently in the older dairy regions where stock has been improved the most by breeding1 more of the disease exists than among the western and southern cattle4 ,illustration ,,fig4 #ba3 ,front view of a tuberculous udder1 showing extent of swelling in single quarter4 ,infectiousness of milk of reacting animals4 ,where the disease appears in the udder the milk almost invariably contains the tubercle organism4 ,under such conditions the appearance of the milk is not materially altered at first1 but as the disease progresses the percentage of fat generally diminishes1 and at times in the more advanced stages where the physical condition of the udder is changed 7,fig4 #ba71 the milk may become watery2 but the percentage of animals showing such udder lesions is not large1 usually not more than a few per cent4 7#d per cent4 according to ,ostertag47 ,on the other hand1 in the earlier phases of the disease1 where its presence has been recognized solely by the aid of the tuberculin test1 before there are any recognizable physical symptoms in any part of the animal1 the milk is generally unaffected4 ,between these extremes1 however1 is found a large proportion of cases1 concerning which so definite data are not available4 ,the results of investigators on this point are conflicting and further information is much desired4 ,some have asserted so long as the udder itself shows no lesions that no tubercle bacilli would be present1#hf but the findings of a considerable number of investigators#hg indicate that even when the udder is apparently not diseased the milk may contain the specific organism as revealed by inoculation experiments upon animals4 ,in some cases1 however1 it has been demonstrated by post-mortem examination that discoverable udder lesions existed that were not recognizable before autopsy was made4 ,in the experimental evidence collected1 a varying percentage of reacting animals were found that gave positive results2 and this number was generally sufficient to indicate that the danger of using milk from reacting animals was considerable1 even though apparently no disease could be found in the udder4 ,the infectiousness of milk can also be proven by the frequent contraction of the disease in other animals1 such as calves and pigs which may be fed on the skim milk4 ,the very rapid increase of the disease among the swine of ,germany and ,denmark1#hh and the frequently reported cases of intestinal infection of young stock also attest the presence of the organism in milk4 ,the tubercle bacillus is so markedly parasitic in its habits1 that1 under ordinary conditions1 it is incapable of growing at normal air temperatures4 ,there is1 therefore1 no danger of the germ developing in milk after it is drawn from the animal1 unless the same is kept at practically blood heat4 ,even though the milk of some reacting animals may not contain the dangerous organism at the time of making the test1 it is quite impossible to foretell how long it will remain free4 ,as the disease becomes more generalized1 or if tuberculous lesions should develop in the udder1 the milk may pass from a healthy to an infectious state4 ,this fact makes it advisable to exclude from milk supplies intended for human use1 all milk of animals that respond to the tuberculin test2 or at least to treat it in a manner so as to render it safe4 ,whether it is necessary to do this or not if the milk is made into butter or cheese is a somewhat different question4 ,exclusion or treatment is rendered more imperative in milk supplies1 because the danger is greater with children with whom milk is often a prominent constituent of their diet1 and also for the reason that the child is more susceptible to intestinal infection than the adult4 ,the danger of infection is much lessened in butter or cheese1 because the processes of manufacture tend to diminish the number of organisms originally present in the milk1 and inasmuch as no growth can ordinarily take place in these products the danger is minimized4 ,moreover1 the fact that these foods are consumed by the individual in smaller amounts than is generally the case where milk is used1 and also to a greater extent by adults1 lessens still further the danger of infection4 ,notwithstanding this1 numerous observers#hi especially in ,germany have succeeded in finding the tubercle bacillus in market butter1 but this fact is not so surprising when it is remembered that a very large fraction of their cattle show the presence of the disease as indicated by the tuberculin test1 a condition that does not obtain in any large section in this country4 ,the observations on the presence of the tubercle bacillus in butter have been questioned somewhat of late#b by the determination of the fact that butter may contain an organism that possesses the property of being stained in the same way as the tubercle organism4 ,differentiation between the two forms is rendered more difficult by the fact that this tubercle-like organism is also capable of producing in animals lesions that stimulate those of tuberculosis1 although a careful examination reveals definite differences4 ,petri#ij has recently determined that both the true tubercle and the acid-resisting butter organism may be readily found in market butter4 ,in the various milk products it has been experimentally determined that the true tubercle bacillus is able to retain its vitality in butter for a number of months and in cheese for nearly a year4 ,treatment of milk from tuberculosis cows4 ,while it has been shown that it is practically impossible to foretell whether the milk of any reacting animal actually contains tubercle bacilli or not1 still the interests of public health demand that no milk from such stock be used for human food until it has been rendered safe by some satisfactory treatment4 #a4 ,heating4 ,by far the best treatment that can be given such milk is to heat it4 ,the temperature at which this should be done depends upon the thermal death point of the tubercle bacillus1 a question concerning which there has been considerable difference of opinion until very recently4 ,according to the work of some of the earlier investigators1 the tubercle bacillus in its vegetative stage is endowed with powers of resistance greater than those possessed by any other pathogenic organism4 ,this work has not been substantiated by the most recent investigations on this subject4 ,in determining the thermal death point of this organism1 as of any other1 not only must the temperature be considered1 but the period of exposure as well1 and where that exposure is made in milk1 another factor must be considered1 viz41 the presence of conditions permitting of the formation of a scalded layer1 for as ,smith#ia first pointed out1 the resistance of the tubercle organism toward heat is greatly increased under these conditions4 ,if tuberculous milk is heated in a closed receptacle where this scalded membrane cannot be produced1 the tubercle bacillus is killed at #adj deg4 ,f4 in #ae to #bj minutes4 ,these results which were first determined by ,smith1 under laboratory conditions1 and confirmed by ,russell and ,hastings1#ib where tuberculous milk was heated in commercial pasteurizers1 have also been verified by ,hesse4#ic ,a great practical advantage which accrues from the treatment of milk at #adj deg4 ,f4 is that the natural creaming is practically unaffected4 ,of course1 where a higher temperature is employed1 the period of exposure may be materially lessened4 ,if milk is momentarily heated to #agf deg4 ,f41 it is certainly sufficient to destroy the tubercle bacillus4 ,this is the plan practiced in ,denmark where all skim milk and whey must be heated to this temperature before it can be taken back to the farm1 a plan which is designed to prevent the dissemination of tuberculosis and foot and mouth disease by means of the mixed creamery by-products4 ,this course renders it possible to utilize with perfect safety1 for milk supplies1 the milk of herds reacting to the tuberculin test1 and as butter of the best quality can be made from cream or milk heated to even high temperatures1#id it thus becomes possible to prevent with slight expense what would otherwise entail a large loss4 #b4 ,dilution4 ,another method that has been suggested for the treatment of this suspected milk is dilution with a relatively large volume of perfectly healthy milk4 ,it is a well known fact that to produce infection1 it requires the simultaneous introduction of a number of organisms1 and in the case of tuberculosis1 especially that produced by ingestion1 this number is thought to be considerable4 ,gebhardt#ie found that the milk of tuberculous cows1 which was virulent when injected by itself into animals1 was innocuous when diluted with #dj to #ajj times its volume of healthy milk4 ,this fact is hardly to be relied upon in practice1 unless the proportion of reacting to healthy cows is positively known4 ,it has also been claimed in the centrifugal separation of cream from milk#if that by far the larger number of tubercle bacilli were thrown out with the separator slime4 ,moore#ig has shown that the tubercle bacilli in an artificially infected milk might be reduced in this way1 so as to be no longer microscopically demonstrable1 yet the purification was not complete enough to prevent the infection of animals inoculated with the milk4 ,another way to exclude all possibility of tubercular infection in milk supplies is to reject all milk from reacting animals4 ,this method is often followed where pasteurization or sterilization is not desired4 ,in dairies where the keeping quality is dependent upon the exclusion of bacteria by stringent conditions as to milking and handling 7sanitary or hygienic milk71 the tuberculin test is frequently used as a basis to insure healthy milk4 ,foot and mouth disease4 ,the wide-spread extension of this disease throughout ,europe in recent years has given abundant opportunity to show that while it is distinctively an animal malady1 it is also transmissible to man1 although the disease is rarely fatal4 ,the causal organism has not been determined with certainty1 but it has been shown that the milk of affected animals possesses infectious properties#ih although appearing unchanged in earlier phases of the disease4 ,hertwig showed the direct transmissibility of the disease to man by experiments made on himself and others4 ,by ingesting milk from an affected animal1 he was able to produce the symptoms of the disease1 the mucous membrane of the mouth being covered with the small vesicles that characterize the malady4 ,it has also been shown that the virus of the disease may be conveyed in butter4#ii ,this disease is practically unknown in this country1 although widely spread in ,europe4 ,there are a number of other bovine diseases such as anthrax1#ajj lockjaw1#aja and hydrophobia#ajb in which it has been shown that the virus of the disease is at times to be found in the milk supply1 but often the milk becomes visibly affected1 so that the danger of using the same is greatly minimized4 ,there are also a number of inflammatory udder troubles known as garget or mammitis4 ,in most of these1 the physical appearance of the milk is so changed1 and often pus is present to such a degree as to give a very disagreeable appearance to the milk4 ,pus-forming bacteria 7staphylococci and streptococci7 are to be found associated with such troubles4 ,a number of cases of gastric and intestinal catarrh have been reported as caused by such milks4#ajc ,,diseases ,,transmissible ,,to ,,man ,,through ,,infection ,,of ,,milk ,,after ,,withdrawal4 ,milk is so well adapted to the development of bacteria in general1 that it is not surprising to find it a suitable medium for the growth of many pathogenic species even at ordinary temperatures4 ,not infrequently1 disease-producing bacteria are able to grow in raw milk in competition with the normal milk bacteria1 so that even a slight contamination may suffice to produce infection4 ,the diseases that are most frequently disseminated in this way are typhoid fever1 diphtheria1 scarlet fever and cholera1 together with the various illy-defined intestinal troubles of a toxic character that occur in children1 especially under the name of cholera infantum1 summer complaint1 etc4 ,diseases of this class are not derived directly from animals because cattle are not susceptible to the same4 ,modes of infection4 ,in a variety of ways1 however1 the milk may be subject to contaminating influences after it is drawn from the animal1 and so give opportunity for the development of disease-producing bacteria4 ,the more important methods of infection are as follows3 #a4 ,infection directly from a pre-existing case of disease on premises4 ,quite frequently a person in the early stage of a diseased condition may continue at his usual vocation as helper in the barn or dairy1 and so give opportunity for direct infection to occur4 ,in the so-called cases of walking typhoid1 this danger is emphasized4 ,it is noteworthy in typhoid fever that the bacilli frequently persist in the urine and in diphtheria they often remain in the throat until after convalescence4 ,in some cases infection has been traced to storage of the milk in rooms in the house where it became polluted directly by the emanations of the patient4#ajd ,among the dwellings of the lower classes where a single room has to be used in common this source of infection has been most frequently observed4 #b4 ,infection through the medium of another person4 ,not infrequently another individual may serve in the capacity of nurse or attendant to a sick person1 and also assist in the handling of the milk1 either in milking the animals or caring for the milk after it has been drawn4 ,busey and ,kober report twenty-one outbreaks of typhoid fever in which dairy employees also acted in the capacity of nurses4 #c4 ,pollution of milk utensils4 ,the most frequent method of infection of cans1 pails1 etc41 is in cleaning them with water that may be polluted with disease organisms4 ,often wells may be contaminated with diseased matter of intestinal origin1 as in typhoid fever1 and the use of water at normal temperatures1 or even in a lukewarm condition1 give conditions permitting of infection4 ,intentional adulteration of milk with water inadvertently taken from polluted sources has caused quite a number of typhoid outbreaks4#aje ,sedgwick and ,chapin#ajf found in the ,springfield1 ,mass41 epidemic of typhoid that the milk cans were placed in a well to cool the milk1 and it was subsequently shown that the well was polluted with typhoid fecal matter4 #d4 ,pollution of udder of animal by wading in infected water1 or by washing same with contaminated water4 ,this method of infection would only be likely to occur in case of typhoid4 ,an outbreak at the ,university of ,virginia in #ahicajg was ascribed to the latter cause4 #e4 ,pollution of creamery by-products1 skim-milk1 etc4 ,where the milk supply of one patron becomes infected with pathogenic bacteria1 it is possible that disease may be disseminated through the medium of the creamery1 the infective agent remaining in the skim milk after separation and so polluting the mixed supply4 ,this condition is more likely to prevail with typhoid because of the greater tolerance of this organism for acids such as would be found in raw milk4 ,the outbreaks at ,brandon1#ajh ,england1 in #ahic1 ,castle ,island1#aji ,ireland1 and ,marlboro1#aaj ,mass41 in #ahid1 were traced to such an origin4 ,while most outbreaks of disease associated with a polluted milk supply originate in the use of the milk itself1 yet infected milk may serve to cause disease even when used in other ways4 ,several outbreaks of typhoid fever have been traced to the use of ice cream where there were strong reasons for believing that the milk used in the manufacture of the product was polluted4#aaa ,hankin#aab details a case of an ,indian confection made largely from milk that caused a typhoid outbreak in a ,british regiment4 ,although the evidence that milk may not infrequently serve as an agent in spreading disease is conclusive enough to satisfactorily prove the proposition1 yet it should be borne in mind that the organism of any specific disease in question has rarely ever been found4 ,the reasons for this are quite the same as those that govern the situation in the case of polluted waters1 except that the difficulties of the problem are much greater in the case of milk than with water4 ,the inability to readily separate the typhoid germ1 for instance1 from the colon bacillus1 an organism frequently found in milk1 presents technical difficulties not easily overcome4 ,the most potent reason of failure to find disease bacteria is the fact that infection in any case must occur sometime previous to the appearance of the outbreak4 ,not only is there the usual period of incubation1 but it rarely happens that an outbreak is investigated until a number of cases have occurred4 ,in this interim the original cause of infection may have ceased to be operative4 ,typhoid fever4 ,with reference to the diseases likely to to be disseminated through the medium of milk1 infected after being drawn from the animal1 typhoid fever is the most important4 ,the reason for this is due 7#a7 to the wide spread distribution of the disease2 7#b7 to the fact that the typhoid bacillus is one that is capable of withstanding considerable amounts of acid1 and consequently finds even in raw milk containing the normal lactic acid bacteria conditions favorable for its growth4#aac ,ability to grow under these conditions can be shown not only experimentally1 but there is abundant clinical evidence that even a slight infection often causes extensive outbreaks1 as in the ,stamford1 ,conn41 outbreak in #ahie where #chf cases developed in a few weeks1 #ig per cent4 of which occurred on the route of one milk-man4 ,in this case the milk cans were thoroughly and properly cleaned1 but were rinsed out with cold water from a shallow well that was found to be polluted4 ,the most common mode of pollution of milk with typhoid organisms is where the milk utensils are infected in one way or another4#aad ,second in importance is the carrying of infection by persons serving in the dual capacity of nurse and dairy attendant4 ,cholera4 ,this germ does not find milk so favorable a nutrient medium as the typhoid organism1 because it is much more sensitive toward the action of acids4 ,kitasato#aae found1 however1 that it could live in raw milk from one to four days1 depending upon the amount of acid present4 ,in boiled or sterilized milk it grows more freely1 as the acid-producing forms are thereby eliminated4 ,in butter it dies out in a few days 7#d to #e74 ,on account of the above relation not a large number of cholera outbreaks have been traced to milk1 but ,simpson#aaf records a very striking case in ,india where a number of sailors1 upon reaching port1 secured a quantity of milk4 ,of the crew which consumed this1 every one was taken ill1 and four out of ten died1 while those who did not partake escaped without any disease4 ,it was later shown that the milk was adulterated with water taken from an open pool in a cholera infected district4 ,diphtheria4 ,milk occasionally1 though not often1 serves as a medium for the dissemination of diphtheria4 ,swithinbank and ,newman#aag cites four cases in which the causal organism has been isolated from milk4 ,it has been observed that growth occurs more rapidly in raw than in sterilized milk4#aah ,infection in this disease is more frequently attributable to direct infection from patient on account of the long persistence of this germ in the throat1 or indirectly through the medium of an attendant4 ,scarlet fever4 ,although it is more difficult to study the relation of this disease to contaminated milk supplies1 because the causal germ of scarlet fever is not yet known1 yet the origin of a considerable number of epidemics has been traced to polluted milk supplies4 ,milk doubtless is infected most frequently from persons in the earlier stages of the disease when the infectivity of the disease is greater4 ,diarrhoeal diseases4 ,milk not infrequently acquires the property of producing diseases of the digestive tract by reason of the development of various bacteria that form more or less poisonous by-products4 ,these troubles occur most frequently during the summer months1 especially with infants and children1 as in cholera infantum and summer complaint4 ,the higher mortality of bottle-fed infants#aai in comparison with those that are nursed directly is explicable on the theory that cows' milk is the carrier of the infection1 because in many cases it is not consumed until there has been ample time for the development of organisms in it4 ,where milk is pasteurized or boiled it is found that the mortality among children is greatly reduced4 ,as a cause of sickness and death these diseases exceed in importance all other specific diseases previously referred to4 ,these troubles have generally been explained as produced by bacteria of the putrefactive class which find their way into the milk through the introduction of filth and dirt at time of milking4#abj ,fluegge#aba has demonstrated that certain peptonizing species possess toxic properties for animals4 ,recent experimental inquiry#abb has demonstrated that the dysentery bacillus 7,shiga7 probably bears a causal relation to some of these summer complaints4 ,ptomaine poisoning4 ,many cases of poisoning from food products are also reported with adults4 ,these are due to the formation of various toxic products1 generally ptomaines1 that are produced as a result of infection of foods by different bacteria4 ,one of these substances1 tyrotoxicon1 was isolated by ,vaughan#abc from cheese and various other products of milk1 and found to possess the property of producing symptoms of poisoning similar to those that are noted in such cases4 ,he attributes the production of this toxic effect to the decomposition of the elements in the milk induced by putrefactive forms of bacteria that develop where milk is improperly kept4#abd ,often outbreaks of this character#abe assume the proportions of an epidemic1 where a large number of persons use the tainted food4 ,,footnotes3 #gh ,hart1 ,trans4 ,int4 ,med4 ,cong41 ,london1 #ahha1 #d3dia-edd4 #gi ,freeman1 ,med4 ,rec41 ,march #bh1 #ahif4 #hj ,busey and ,kober1 ,rept4 ,health ,off4 of ,dist4 of ,col41 ,washington1 ,d4 ,c41 #ahie1 p4 #bii4 ,these authors present in this report an elaborate article on morbific and infectious milk1 giving a very complete bibliography of #ahj numbers4 ,they append to ,hart's list 7which is published in full7 additional outbreaks which have occurred since1 together with full data as to extent of epidemic1 circumstances governing the outbreak1 as well as name of original reporter and reference4 #ha ,smith1 ,theo41 ,journ4 of ,expt4 ,med41 #ahih1 #c3dea4 #hb ,dinwiddie1 ,bull4 #eg1 ,ark4 ,expt4 ,stat41 ,june1 #ahii2 ,ravenel1 ,univ4 of ,penn4 ,med4 ,bull41 ,sept4 #aija4 #hc ,ravenel1 ,journ4 of ,comp4 ,med4 ,vet4 ,arch41 ,dec4 #ahig2 ,hartzell1 ,journ4 ,amer4 ,med4 ,ass'n1 ,april #af1 #ahih4 #hd ,stille1 ,brit4 ,med4 ,journ41 ,aug4 #ai1 #ahii4 #he ,this test is made by injecting into the animal a small quantity of tuberculin1 which is a sterilized glycerin extract of cultures of the tubercle bacillus4 ,in a tuberculous animal1 even in the very earliest phases of the disease1 tuberculin causes a temporary fever that lasts for a few hours4 ,by taking the temperature a number of times before and after injection it is possible to readily recognize any febrile condition4 ,a positive diagnosis is made where the temperature after inoculation is at least #b4j deg4 ,f4 above the average normal1 and where the reaction fever is continued for a period of some hours4 #hf ,martin1 ,brit4 ,med4 ,journ4 #ahie1 #a3icg2 ,nocard1 ,les ,tuberculoses animales1 #ahie4 #hg ,c4 ,o4 ,jensen1 ,milch ,kunde und ,milch hygiene1 p4 #fi4 #hh ,ostertag1 ,milch ,zeit41 #bb3fgb4 #hi ,obermueller1 ,hyg4 ,rund41 #ahig1 p4 #gab2 ,petri1 ,arb4 a4 d4 ,kais4 ,ges4 ,amte1 #ahih1 #ad3 #a2 ,hormann und ,morgenroth1 ,hyg4 ,rund41 #ahih1 p4 #bag4 #ij ,rabinowitsch1 ,zeit4 f4 ,hyg41 #ahig1 #bf3 #ij4 #ia ,th4 ,smith4 ,journ4 of ,expt4 ,med41 #ahii1 #d3bag4 #ib ,russell and ,hastings1 #ah ,rept4 ,wis4 ,expt4 ,stat41 #aija4 #ic ,hesse1 ,zeit4 f4 ,hyg41 #aijj1 #cd3cdf4 #id ,practically all of the finest butter made in ,denmark is made from cream that has been pasteurized at temperatures varying from #afj deg4-#ahe deg4 ,f4 #ie ,gebhardt1 ,virch4 ,arch41 #ahij1 #aai3ab4 #if ,scheurlen1 ,arb4 a4 d4 k4 ,ges4 ,amte1 #ahia1 #g3bfi2 ,bang1 ,milch ,zeit41 #ahic1 p4 #fgb4 #ig ,moore1 ,year ,book of ,u4 ,s4 ,dept4 ,agr41 #ahie1 p4 #dcb4 #ih ,weigel and ,noack1 ,jahres4 d4 ,ges4 ,med41 #ahij1 p4 #fdb2 ,weissenberg1 ,allg4 med4 ,cent4 ,zeit41 #ahij1 p4 #a2 ,baum1 ,arch4 f4 ,thierheilkunde1 #ahib1 #ah3af4 #ii ,schneider1 ,muench1 med4 ,wochenschr41 #ahic1 ,no4 #bg2 ,froehner1 ,zeit f4 ,fleisch u4 ,milchhygiene1 #ahia1 p4 #ee4 #ajj ,feser1 ,deutsche ,zeit4 f4 ,thiermed41 #ahhj1 #f3aff4 #aja ,nocard1 ,bull4 ,gen41 #ahhe1 p4 #ed4 #ajb ,deutsche ,viertelsjahr4 f4 offentl4 ,gesundheitspflege1 #ahij1 #bj3ddd4 #ajc ,zeit4 f4 ,fleisch und ,milch hygiene1 #aa3aad4 #ajd ,e4 ,roth1 ,deutsche ,vierteljahresschr4 f4 offentl4 ,gesundheitspfl41 #ahij1 #bb3bch #aje ,s4 ,w4 ,north1 ,london ,practitioner1 #ahhi1 #dc3cic4 #ajf ,sedgwick and ,chapin1 ,boston ,med4 ,surg4 ,journ41 #ahic1 #abi3dhe4 #ajg ,dabney1 ,phila4 ,med4 ,news1 #ahic1 #fc3fcj4 #ajh ,welphy1 ,london ,lancet1 #ahid1 #b3ajhe4 #aji ,brit4 ,med4 ,journ41 #ahid1 #a3hae4 #aaj ,mass4 ,bd4 ,health ,rept41 #ahid1 p4 #gfe4 #aaa ,turner1 ,london ,practitioner1 #ahib1 #di3ada2 ,munro1 ,brit4 ,med4 ,journ41 #ahid1 #b3hbi4 #aab ,hankin1 ,brit4 ,med4 ,journ41 #ahid1 #b3fac4 #aac ,heim 7,arb4 a4 d4 ,kais4 ,gesundheitsamte1 #ahhi1 #e3cjc7 finds it capable of living from #bj-cj days in milk4 #aad ,schueder 7,zeit4 f4 ,hyg41 #aijb1 #ch3cd7 examined the statistics of #fch typhoid epidemics4 ,he found #ga per cent4 due to infected drinking water1 #ag per cent4 to infected milk1 and #c4e per cent4 caused by other forms of food4 #aae ,kitasato4 ,arb4 a4 d4 ,kais4 ,gesundheitsamte1 #a3dgj4 #aaf ,simpson1 ,london ,practitioner1 #ahhg1 #ci3add4 #aag ,swithinbank and ,newman1 ,bacteriology of ,milk1 p4 #cda4 #aah ,schottelius and ,ellerhorst4 ,milch ,zeit41 #ahig1 pp4 #dj and #gc4 #aai ,baginsky1 ,hyg4 ,rund41 #ahie1 p4 #agf4 #abj ,gaffky1 ,deutsch4 med4 ,wochen41 #ah3ad4 #aba ,fluegge4 ,zeit41 f4 ,hyg41 #ag3bgb1 #ahid4 #abb ,duval and ,bassett1 ,studies from the ,rockefeller ,inst4 for ,med4 ,research1 #b3g1 #aijd4 #abc ,zeit4 f4 physiol4 ,chemie1 #aj3adf2 #i ,intern4 ,hyg4 ,cong4 7,london71 #ahia1 p4 #aah4 #abd ,vaughan and ,perkins1 ,arch4 f4 ,hyg41 #bg3cjh4 #abe ,newton and ,wallace 7,phila4 ,med4 ,news1 #ahhg1 #ej3egj7 report three outbreaks at ,long ,branch1 ,n4 ,j41 two of which occurred in summer hotels4 ,,chapter ,,vi4 ,,bacteria ,,and ,,milk ,,supplies ,,with ,,especial ,,reference ,,to ,,methods ,,of ,,preservation4 ,to the milk dealer or distributor1 bacteria are more or less of a detriment4 ,none of the organisms that find their way into milk1 nor the by-products formed by their growth1 improve the quality of milk supplies4 ,it is therefore especially desirable from the milk-dealer's point of view that these changes should be held in abeyance as much as possible4 ,then too1 the possibility that milk may serve as a medium for the dissemination of disease-breeding bacteria makes it advisable to protect this food supply from all possible infection from suspicious sources4 ,in considering1 therefore1 the relation of bacteria to general milk supplies1 the economic and the hygienic standpoints must be taken into consideration4 ,ordinarily much more emphasis is laid upon the first requirement4 ,if the supply presents no abnormal feature as to taste1 odor and appearance1 unfortunately but little attention is paid to the possibility of infection by disease germs4 ,the methods of control which are applicable to general milk supplies are based on the following foundations3 7#a7 the exclusion of all bacterial life1 as far as practicable1 at the time the milk is drawn1 and the subsequent storage of the same at temperatures unfavorable for the growth of the organisms that do gain access2 7#b7 the removal of the bacteria1 wholly or in part1 after they have once gained access4 ,until within comparatively recent years1 practically no attention was given to the character of milk supplies1 except possibly as to the percentage of butter fat1 and sometimes the milk solids which it contained4 ,so long as the product could be placed in the hands of the consumer in such shape as not to be rejected by him as unfit for food1 no further attention was likely to be given to its character4 ,at present1 however1 much more emphasis is being given to the quality of milk1 especially as to its germ content2 and the milk dealer is beginning to recognize the necessity of a greater degree of control4 ,this control must not merely concern the handling of the product after it reaches him1 but should go back to the milk producer on the farm4 ,here especially1 it is necessary to inculcate those methods of cleanliness which will prevent in large measure the wholesale infection that ordinarily occurs4 ,the two watch words which are of the utmost importance to the milk dealer are cleanliness and cold4 ,if the milk is properly drawn from the animal in a clean manner and is immediately and thoroughly chilled1 the dealer has little to fear as to his product4 ,whenever serious difficulties do arise1 attributable to bacterial changes1 it is because negligence has been permitted in one or both directions4 ,the influence of cleanliness in diminishing the bacterial life in milk and that of low temperatures in repressing the growth of those forms which inevitably gain access has been fully dealt with in preceding chapters4 ,it is of course not practicable to take all of these precautions to which reference has been made in the securing of large supplies of market milk for city use1 but great improvement over existing conditions could be secured if the public would demand a better supervision of this important food article4 ,boards of health in our larger cities are awakening to the importance of this question and are becoming increasingly active in the matter of better regulations and the enforcement of the same4 ,new ,york ,city ,board of ,health has taken an advanced position in requiring that all milk sold in the city shall be chilled down to #de deg4 ,f4 immediately after milking and shall be transported to the city in refrigerator cars4 ,reference has already been made to the application of the acid test 7page #eb7 in the inspection of city milk supplies1 and it is the opinion of the writer that the curd test 7see page #gf7 could also be used with advantage in determining the sanitary character of milk4 ,this test reveals the presence of bacteria usually associated with dirt and permits of the recognition of milks that have been carelessly handled4 ,from personal knowledge of examinations made of the milk supplies in a number of ,wisconsin cities it appears that this test could be utilized with evident advantage4 ,sanitary or certified milk supplies4 ,in a number of the larger cities1 the attempt has been made to improve the quality of the milk supplies by the installation of dairies in which is produced an especially high grade of milk4 ,frequently the inspection of the dairy as well as the examination of the milk at stated intervals is under the control of milk commissions or medical societies and as it is customary to distribute the certificate of the examining board with the product1 such milks are frequently known as certified4 ,in such dairies the tuberculin test is used at regular intervals1 and the herd inspected frequently by competent veterinarians4 ,the methods of control inaugurated as to clean milking and subsequent handling are such as to insure the diminution of the bacteria to the lowest possible point4 ,the bacterial limit set by the ,pediatric ,society of ,philadelphia is #aj1jjj organisms per cc4 ,often it is possible to improve very materially on this standard and not infrequently is the supply produced where it contains only a few thousand organisms per cc4 ,where such a degree of care is exercised1 naturally a considerably higher price must be paid for the product1#abf and it should be remembered that the development of such a system is only possible in relatively large centers where the dealer can cater to a selected high-class trade4 ,moreover1 it should also be borne in mind that such a method of control is only feasible in dairies that are under individual control4 ,the impossibility of exercising adequate control with reference to the milking process and the care which should be given the milk immediately thereafter1 when the same is produced on different farms under various auspices is evident4 ,,preservation ,,of ,,milk ,,supplies4 ,while much can be done to improve the quality of milk supplies by excluding a large proportion of the bacteria which normally gain access to the milk1 and preventing the rapid growth of those that do find their way therein1 yet for general municipal purposes1 any practical method of preservation#abg that is applicable on a commercial scale must rest largely upon the destruction of bacteria that are present in the milk4 ,the two possible methods by which bacteria can be destroyed after they have once gained access is 7#a7 by the use of chemical preservatives2 7#b7 by the aid of physical methods4 ,chemical preservatives4 ,numerous attempts have been made to find some chemical substance that could be added to milk which would preserve it without interfering with its nutritive properties1 but as a general rule a substance that is toxic enough to destroy or inhibit the growth of bacterial life exerts a prejudicial effect on the tissues of the body4 ,the use of chemicals1 such as carbolic acid1 mercury salts and mineral acids1 that are able to entirely destroy all life1 is of course excluded1 except when milk is preserved for analytical purposes2 but a number of milder substances are more or less extensively employed1 although the statutes of practically all states forbid their use4 ,the substances so used may be grouped in two classes3 #a4 ,those that unite chemically with certain by-products of bacterial growth to form inert substances4 ,thus bicarbonate of soda neutralizes the acid in souring milk1 although it does not destroy the lactic acid bacteria4 #b4 ,those that act directly upon the bacteria in milk1 restraining or inhibiting their development4 ,the substances most frequently utilized are salicylic acid1 formaldehyde and boracic acid4 ,these are nearly always sold to the milk handler1 under some proprietary name1 at prices greatly in excess of what the crude chemicals could be bought for in the open market4 ,formaldehyde has been widely advertised of late1 but its use is fraught with the greatest danger1 for it practically renders insoluble all albuminous matter and its toxic effect is greatly increased in larger doses4 ,these substances are generally used by milk handlers who know nothing of their poisonous action1 and although it may be possible for adults to withstand their use in dilute form1 without serious results1 yet their addition to general milk supplies that may be used by children is little short of criminal4 ,the sale of these preparations for use in milk finds its only outlet with those dairymen who are anxious to escape the exactions that must be met by all who attempt to handle milk in the best possible manner4 ,farrington has suggested a simple means for the detection of preservalin 7boracic acid74#abh ,when this substance is added to fresh milk1 it increases the acidity of milk without affecting its taste4 ,as normal milk tastes sour when it contains about #j4c per cent lactic acid1 a milk that tests as much or more than this without tasting sour has been probably treated with this antiseptic agent4 ,physical methods of preservation4 ,methods based upon the application of physical forces are less likely to injure the nutritive value of milk1 and are consequently more effective1 if of any value whatever4 ,a number of methods have been tried more or less thoroughly in an experimental way that have not yet been reduced to a practical basis1 as electricity1 use of a vacuum1 and increased pressure4#abi ,condensation has long been used with great success1 but in this process the nature of the milk is materially changed4 ,the keeping quality in condensed milk often depends upon the action of another principle1 viz41 the inhibition of bacterial growth by reason of the concentration of the medium4 ,this condition is reached either by adding sugar and so increasing the soluble solids1 or by driving off the water by evaporation1 preferably in a vacuum pan4 ,temperature changes are1 however1 of the most value in preserving milk1 for by a variation in temperature all bacterial growth can be brought to a standstill1 and under proper conditions thoroughly destroyed4 ,use of low temperatures4 ,the effect of chilling or rapid cooling on the keeping quality of milk is well known4 ,when the temperature of milk is lowered to the neighborhood of #de deg4 ,f41 the development of bacterial life is so slow as to materially increase the period that milk remains sweet4 ,within recent years1 attempts have been made to preserve milk so that it could be shipped long distances by freezing the product1 which in the form of milk-ice could be held for an indefinite period without change4#acj ,a modification of this process known as ,casse's system has been in use more or less extensively in ,copenhagen and in several places in ,germany4 ,this consists of adding a small block of milk-ice 7frozen milk7 to large cans of milk 7one part to about fifty of milk7 which may or may not be pasteurized4#aca ,this reduces the temperature so that the milk remains sweet considerably longer4 ,such a process might permit of the shipment of milk for long distances with safety but as a matter of fact1 the system has not met with especial favor4 ,illustration3 ,,fig4 #bb4 ,microscopic appearance of normal milk showing the fat-globules aggregated in clusters4 ,use of high temperatures4 ,heat has long been used as a preserving agent4 ,milk has been scalded or cooked to keep it from time immemorial4 ,heat may be used at different temperatures1 and when so applied exerts a varying effect1 depending upon temperature employed4 ,all methods of preservation by heat rest1 however1 upon the application of the heat under the following conditions3 #a4 ,a temperature above the maximum growing-point 7#aje deg4-#aae deg4 ,f47 and below the thermal death-point 7#acj deg4-#adj deg4 ,f47 will prevent further growth1 and consequently fermentative action4 #b4 ,a temperature above the thermal death-point destroys bacteria1 and thereby stops all changes4 ,this temperature varies1 however1 with the condition of the bacteria1 and for spores is much higher than for vegetative forms4 ,attempts have been made to employ the first principle in shipping milk by rail1 viz41 prolonged heating above growing temperature1 but when milk is so heated1 its physical appearance is changed4#acb ,the methods of heating most satisfactorily used are known as sterilization and pasteurization1 in which a degree of temperature is used approximating the boiling and scalding points respectively4 ,illustration3 ,,fig4 #bc4 ,microscopic appearance of milk heated above #adj deg4 ,f41 showing the homogeneous distribution of fat-globules4 ,the physical change noted in comparison with ,fig4 #bb causes the diminished consistency of pasteurized cream4 ,effect of heat on milk4 ,when milk is subjected to the action of heat1 a number of changes in its physical and chemical properties are to be noted4 #a4 ,diminished body4 ,when milk1 but more especially cream1 is heated to #adj deg4 ,f4 or above1 it becomes thinner in consistency or body1 a condition which is due to a change in the grouping of the fat globules4 ,in normal milk1 the butter fat for the most part is massed in microscopic clots as 7,fig4 #bb74 ,when exposed to #adj deg4 ,f4 or above for ten minutes these fat-globule clots break down1 and the globules become homogeneously distributed 7,fig4 #bc74 ,a momentary exposure to heat as high as #aeh deg4-#afj deg4 may be made without serious effect on the cream lime2 but above this the cream rises so poorly and slowly that it gives the impression of thinner milk4 #b4 ,cooked ,taste4 ,if milk is heated for some minutes to #afj deg4 ,f41 it acquires a cooked taste that becomes more pronounced as the temperature is further raised4 ,milk so heated develops on its surface a pellicle or skin4 ,the cause of this change in taste is not well known4 ,usually it has been explained as being produced by changes in the nitrogenous elements in the milk1 particularly in the albumen4 ,thoerner#acc has pointed out the coincidence that exists between the appearance of a cooked taste and the loss of certain gases that are expelled by heating4 ,he finds that the milk heated in closed vessels from which the gas cannot escape has a much less pronounced cooked flavor than if heated in an open vessel4 ,the so-called skin on the surface of heated milk is not formed when the milk is heated in a tightly-closed receptacle4 ,by some#acd it is asserted that this layer is composed of albumen1 but there is evidence to show that it is modified casein due to the rapid evaporation of the milk serum at the surface of the milk4 #c4 ,digestibility4 ,considerable difference of opinion has existed in the minds of medical men as to the relative digestibility of raw and heated milks4 ,a considerable amount of experimental work has been done by making artificial digestion experiments with enzyms1 also digestion experiments with animals1 and in a few cases with children4 ,the results obtained by different investigators are quite contradictory1 although the preponderance of evidence seems to be in favor of the view that heating does impair the digestibility of milk1 especially if the temperature attains the sterilizing point4#ace ,it has been observed that there is a noteworthy increase in amount of rickets1#acf scurvy and marasmus in children where highly-heated milks are employed4 ,these objections do not obtain with reference to milk heated to moderate temperatures1 as in pasteurization1 although even this lower temperature lessens slightly its digestibility4 ,the successful use of pasteurized milks in children's hospitals is evidence of its usefulness4 #d4 ,fermentative changes4 ,the normal souring change in milk is due to the predominance of the lactic acid bacteria1 but as these organisms as a class do not possess spores1 they are readily killed when heated above the thermal death-point of the developing cell4 ,the destruction of the lactic forms leaves the spore-bearing types possessors of the field1 and consequently the fermentative changes in heated milk are not those that usually occur1 but are characterized by the curdling of the milk from the action of rennet enzyms4 #e4 ,action of rennet4 ,heating milk causes the soluble lime salts to be precipitated1 and as the curdling of milk by rennet 7in cheese-making7 is dependent upon the presence of these salts1 their absence in heated milks greatly retards the action of rennet4 ,this renders it difficult to utilize heated milks in cheese-making unless the soluble lime salts are restored1 which can be done by adding solutions of calcium chlorid4 ,sterilization4 ,as ordinarily used in dairying1 sterilization means the application of heat at temperatures approximating1 if not exceeding1 #bab deg4 ,f4 ,it does not necessarily imply that milk so treated is sterile1 i4 e41 germ-free2 for1 on account of the resistance of spores1 it is practically impossible to destroy entirely all these hardy forms4 ,if milk is heated at temperatures above the boiling point1 as is done where steam pressure is utilized1 it can be rendered practically germ-free4 ,such methods are employed where it is designed to keep milk sweet for a long period of time4 ,the treatment of milk by sterilization has not met with any general favor in this country1 although it has been more widely introduced abroad4 ,in most cases the process is carried out after the milk is bottled2 and considerable ingenuity has been exercised in the construction of devices which will permit of the closure of the bottles after the sterilizing process has been completed4 ,milks heated to so high a temperature have a more or less pronounced boiled or cooked taste1 a condition that does not meet with general favor in this country4 ,the apparatus suitable for this purpose must1 of necessity1 be so constructed as to withstand steam pressure1 and consequently is considerably more expensive than that required for the simpler pasteurizing process4 ,pasteurization4 ,in this method the degree of heat used ranges from #adj deg4 to #ahe deg4 ,f4 and the application is made for only a limited length of time4 ,the process was first extensively used by ,pasteur 7from whom it derives its name7 in combating various maladies of beer and wine4 ,its importance as a means of increasing the keeping quality of milk was not generally recognized until a few years ago2 but the method is now growing rapidly in favor as a means of preserving milk for commercial purposes4 ,the method does not destroy all germ-life in milk2 it affects only those organisms that are in a growing1 vegetative condition2 but if the milk is quickly cooled1 it enhances the keeping quality very materially4 ,it is unfortunate that this same term is used in connection with the heating of cream as a preparatory step to the use of pure cultures in cream-ripening in butter-making4 ,the objects to be accomplished vary materially and the details of the two processes are also quite different4 ,while pasteurizing can be performed on a small scale by the individual1 the process can also be adapted to the commercial treatment of large quantities of milk4 ,the apparatus necessary for this purpose is not nearly so expensive as that used in sterilizing1 a factor of importance when other advantages are considered4 ,in this country pasteurization has made considerable headway1 not only in supplying a milk that is designed to serve as children's food1 but even for general purposes4 ,requirements essential in pasteurization4 ,while considerable latitude with reference to pasteurizing limits is permitted1 yet there are certain conditions which should be observed1 and these1 in a sense1 fix the limits that should be employed4 ,these may be designated as 7#a7 the physical1 and 7#b7 the biological requirements4 ,physical requirements4 #a4 ,avoidance of scalded or cooked taste4 ,the ,english and ,american people are so averse to a scalded or cooked flavor in milk that it is practically impossible for a highly heated product to be sold in competition with ordinary raw milk4 ,in pasteurization then1 care must be taken not to exceed the temperature at which a permanently cooked flavor is developed4 ,as previously observed1 this point varies with the period of exposure4 ,a momentary exposure to a temperature of about #agj deg4 ,f4 may be made without any material alteration1 but if the heat is maintained for a few minutes 7ten minutes or over71 a temperature of #aeh deg4 to #afj deg4 ,f4 is about the maximum that can be employed with safety4 #b4 ,normal creaming of the milk4 ,it is especially desirable that a sharp and definite cream line be evident on the milk soon after pasteurization4 ,if this fails to appear1 the natural inference of the consumer is that the milk is skimmed4 ,if the milk be heated to a temperature sufficiently high to cause the fat-globule clusters to disintegrate 7see ,figs4 #bb and #bc71 the globules do not rise to the surface as readily as before and the cream line remains indistinct4 ,where the exposure is made for a considerable period of time 7#aj minutes or more71 the maximum temperature which can be used without producing this change is about #adj deg4 ,f42 if the exposure is made for a very brief time1 a minute or less1 the milk may be heated to #aeh deg4-#afj ,f4 deg4 without injuring the creaming property4 #c4 ,no diminution in cream body4 ,coincident with this change which takes place in the creaming of the milk is the change in body or consistency which is noted where cream is pasteurized at too high a temperature4 ,for the same reason as given under 7#b7 cream heated above these temperatures is reduced in apparent thickness and appears to contain less butter-fat4 ,of course the pasteurizing process does not change the fat content1 but its body is apparently so affected4 ,thus a #be per cent4 cream may seem to be no thicker or heavier than an #ah per cent4 raw cream4 ,this real reduction in consistency naturally affects the readiness with which the cream can be whipped4 ,biological requirements4 #a4 ,enhanced keeping quality4 ,in commercial practice the essential biological requirement is expressed in the enhanced keeping quality of the pasteurized milk4 ,this expresses in a practical way the reduction in germ life accomplished by the pasteurizing process4 ,the improvement in keeping quality depends upon the temperature and time of exposure1 but fully as much also on the way in which the pasteurized product is handled after heating4 ,the lowest temperature which can be used with success to kill the active1 vegetative bacteria is about #adj deg4 ,f41 at which point it requires about ten minutes exposure4 ,if this period is curtailed the temperature must be raised accordingly4 ,an exposure to a temperature of #age deg4 ,f4 for a minute has approximately the same effect as the lower degree of heat for the longer time4 ,the following bacteriological studies as to the effect which a variation in temperature exerts on bacterial life in milk are of importance as indicating the foundation for the selection of the proper limits4 ,in the following table the exposures were made for a uniform period 7#bj minutes73 ,the bacterial content of milk heated at different temperatures4 ,number of bacteria per cc4 in milk4 #de deg4 ,c4 #ej deg4 ,c4 #ee deg4 ,c4 #fj deg4 ,c4 #fe deg4 ,c4 #gj deg4 ,c4 ,unheated #aac deg4 ,f4 #abb deg4 ,f4 #aca deg4 ,f4 #adj deg4 ,f4 #adi deg4 ,f4 #aeh deg4 ,f4 ,series ,i4 #b1hie1jjj ---- #a1bfj1jjj #gih1jjj #cb1jjj #e1ggj #c1ijj ,series ,,ii4 #gej1jjj #ffe1jjj #bfb1djj #bja1jjj #iej #gjj #gje ,series ,,iii4 #a1cej1jjj #a1ajj1jjj #bfj1jjj #bae1jjj #ege #faj #fej ,series ,,iv4 #a1gej1jjj ---- #hg1cfj ---- #d1jjj #c1ejj #c1fjj ,it appears from these results that the most marked decrease in temperature occurs at #adj deg4 ,f4 7#fj deg4 ,c474 ,it should also be observed that an increase in heat above this temperature did not materially diminish the number of organisms present1 indicating that those forms remaining were in a spore or resistant condition4 ,it was noted1 however1 that the developing colonies grew more slowly in the plates made from the highly heated milk1 showing that their vitality was injured to a greater extent even though not killed4 #b4 ,destruction of disease bacteria4 ,while milk should be pasteurized so as to destroy all active1 multiplying bacteria1 it is particularly important to destroy any organisms of a disease nature that might find their way into the same4 ,fortunately most of the bacteria capable of thriving in milk before or after it is drawn from the animal are not able to form spores and hence succumb to proper pasteurization4 ,such is the case with the diphtheria1 cholera and typhoid organisms4 ,the organism that is invested with most interest in this connection is the tubercle bacillus4 ,on account of its more or less frequent occurrence in milk and its reputed high powers of resistance1 it may well be taken as a standard in pasteurizing4 ,thermal death limits of tubercle bacillus4 ,concerning the exact temperature at which this germ is destroyed there is considerable difference of opinion4 ,part of this arises from the inherent difficulty in determining exactly when the organism is killed 7due to its failure to grow readily on artificial media71 and part from the lack of uniform conditions of exposure4 ,the standards that previously have been most generally accepted are those of ,de ,man1#acg who found that thirty minutes exposure at #adi deg4 ,f41 fifteen minutes at #aee deg4 ,f41 or ten minutes at #afg deg4 ,f41 sufficed to destroy this germ4 ,more recently it has been demonstrated1#ach and these results confirmed1#aci that if tuberculous milk is heated in closed receptacles where the surface pellicle does not form1 the vitality of this disease germ is destroyed at #adj deg4 ,f4 in #aj-ae minutes1 while an exposure at #afj deg4 ,f4 requires only about one minute4#adj ,if the conditions of heating are such that the surface of the milk is exposed to the air1 the resistance of bacteria is greatly increased4 ,when heated in open vessels ,smith found that the tubercle organism was not killed in some cases where the exposure was made for at least an hour4 ,russell and ,hastings#ada have shown an instance where the thermal death-point of a micrococcus isolated from pasteurized milk was increased #ab4e deg4 ,f41 by heating it under conditions that permitted of the formation of the scalded layer4 ,it is therefore apparent that apparatus used for pasteurization should be constructed so as to avoid this defect4 ,methods of treatment4 ,two different systems of pasteurization have grown up in the treatment of milk4 ,one of these has been developed from the hygienic or sanitary aspect of the problem and is used more particularly in the treatment of cream and relatively small milk supplies4 ,the other system has been developed primarily from the commercial point of view where a large amount of milk must be treated in the minimum time4 ,in the first method the milk is heated for a longer period of time1 about fifteen minutes at a relatively low temperature from #adj deg4-#aee deg4 ,f42 in the other1 the milk is exposed to the source of heat only while it is passing rapidly through the apparatus4 ,naturally1 the exposure under such conditions must be made at a considerably higher temperature1 usually in the neighborhood of #afj deg4 ,f4 ,the types of apparatus used in these respective processes naturally varies4 ,where the heating is prolonged1 the apparatus employed is built on the principle of a tank or reservoir in which a given volume of milk may be held at any given temperature for any given period of time4 ,when the heat is applied for a much shorter period of time1 the milk is passed in a continuous stream through the machine4 ,naturally the capacity of a continuous-flow apparatus is much greater than a machine that operates on the intermittent principle2 hence1 for large supplies1 as in city distribution1 this system has a great advantage4 ,the question as to relative efficiency is however one which should be given most careful consideration4 ,pasteurizing apparatus4 ,the problems to be solved in the pasteurization of milk and cream designed for direct consumption are so materially different from where the process is used in butter-making that the type of machinery for each purpose is quite different4 ,the equipment necessary for the first purpose may be divided into two general classes3 #a4 ,apparatus of limited capacity designed for family use4 #b4 ,apparatus of sufficient capacity to pasteurize on a commercial scale4 ,domestic pasteurizers4 ,in pasteurizing milk for individual use1 it is not desirable to treat at one time more than will be consumed in one day2 hence an apparatus holding a few bottles will suffice4 ,in this case the treatment can best be performed in the bottle itself1 thereby lessening the danger of infection4 ,several different types of pasteurizers are on the market2 but special apparatus is by no means necessary for the purpose4 ,the process can be efficiently performed by any one with the addition of an ordinary dairy thermometer to the common utensils found in the kitchen4 ,fig4 #bd indicates a simple contrivance that can be readily arranged for this purpose4 ,the following suggestions indicate the different steps of the process3 #a4 ,use only fresh milk4 #b4 ,place milk in clean bottles or fruit cans1 filling to a uniform level1 closing bottles tightly with a cork or cover4 ,if pint and quart cans are used at the same time1 an inverted bowl will equalize the level4 ,set these in a flat-bottomed tin pail and fill with warm water to same level as milk4 ,an inverted pie tin punched with holes will serve as a stand on which to place the bottles during the heating process4 #c4 ,heat water in pail until the temperature of same reaches #aee deg4 to #afj deg4 ,f42 then remove from source of direct heat1 cover with a cloth or tin cover1 and allow the whole to stand for half an hour4 ,in the preparation of milk for children1 it is not advisable to use the low-temperature treatment 7#adj deg4 ,f47 that is recommended for commercial city delivery4 ,illustration3 ,,fig4 #bd4 ,a home-made pasteurizer4 #d4 ,remove bottles of milk and cool them as rapidly as possible without danger to bottles and store in a refrigerator4 ,commercial pasteurizers4 ,the two methods of pasteurization practiced commercially for the preservation of milk and cream have been developed because of the two types of machinery now in use4 ,apparatus constructed on the reservoir or tank principle permits of the retention of the milk for any desired period of time4 ,therefore1 a lower temperature can be employed in the treatment4 ,in those machines where the milk flows through the heater in a more or less continuous stream1 the period of exposure is necessarily curtailed1 thereby necessitating a higher temperature4 ,reservoir pasteurizers4 ,the simplest type of apparatus suitable for pasteurizing on this principle is where the milk is placed in shotgun cans and immersed in water heated by steam4 ,ordinary tanks surrounded with water spaces can also be used successfully4 ,the ,boyd cream ripening vat has also been tried4 ,in this the milk is heated by a swinging coil immersed in the vat through which hot water circulates4 ,in #ahid the writer#adb constructed a tank pasteurizer which consisted of a long1 narrow vat surrounded by a steam-heated water chamber4 ,both the milk and the water chambers were provided with mechanical agitators having a to-and-fro movement4 ,illustration3 ,,fig4 #be4 ,pott's pasteurizer4 ,another machine which has been quite generally introduced is the ,potts' rotating pasteurizer4 ,this apparatus has a central milk chamber that is surrounded with an outer shell containing hot water4 ,the whole machine revolves on a horizontal axis1 and the cream or milk is thus thoroughly agitated during the heating process4 ,continuous-flow pasteurizers4 ,the demand for greater capacity than can be secured in the reservoir machines has led to the perfection of several kinds of apparatus where the milk is heated momentarily as it flows through the apparatus4 ,most of these were primarily introduced for the treatment of cream for butter-making purposes1 but they are frequently employed for the treatment of milk on a large scale in city milk trade4 ,many of them are of ,european origin although of late years several have been devised in this country4 ,the general principle of construction is much the same in most of them4 ,the milk is spread out in a thin sheet1 and is treated by passing it over a surface1 heated either with steam directly or preferably with hot water4 ,where steam is used directly1 it is impossible to prevent the scalding on of the milk proteids to the heated surface4 ,in some of these machines 7,thiel1 ,kuehne1 ,lawrence1 ,de ,laval1 and ,hochmuth71 a ribbed surface is employed over which the milk flows1 while the opposite surface is heated with hot water or steam4 ,monrad1 ,lefeldt and ,lentsch employ a centrifugal apparatus in which a thin layer of milk is heated in a revolving drum4 ,in some types of apparatus1 as in the ,miller machine1 an ,american pasteurizer1 the milk is forced in a thin sheet between two heated surfaces1 thereby facilitating the heating process4 ,in the ,farrington machine heated discs rotate in a reservoir through which the milk flows in a continuous stream4 ,one of the most economical types of apparatus is the regenerator type 7a ,german machine71 in which the milk passes over the heating surface in a thin stream and then is carried back over the incoming cold milk so that the heated liquid is partially cooled by the inflowing fresh milk4 ,in machines of this class it requires very much less steam to heat up the milk than in those in which the cold milk is heated wholly by the hot water4 ,a number of machines have been constructed on the principle of a reservoir which is fed by a constantly flowing stream4 ,in some kinds of apparatus of this type no attempt is made to prevent the mixing of the recently introduced milk with that which has been partially heated4 ,the pattern for this reservoir type is ,fjord's heater1 in which the milk is stirred by a stirrer4 ,this apparatus was originally designed as a heater for milk before separation1 but it has since been materially modified so that it is better adapted to the purposes of pasteurization4 ,reid was the first to introduce this type of machine into ,america4 ,objections to continuous flow pasteurizers4 ,in all continuous flow pasteurizers certain defects are more or less evident4 ,while they fulfill the important requirement of large capacity1 an absolute essential where large volumes of milk are being handled1 it does not of necessity follow that they conform to all the hygienic and physical requirements that should be kept in mind4 ,the greatest difficulty is the shortened period of exposure4 ,the period which the milk is actually heated is often not more than a minute or so4 ,another serious defect is the inability to heat all of the milk for a uniform period of time4 ,at best1 the milk is exposed for an extremely short time1 but even then portions pass through the machine much more quickly than do the remainder4 ,those portions in contact with the walls of the apparatus are retarded by friction and are materially delayed in their passage1 while the particles in the center of the stream1 however thin1 flow through in the least possible time4 ,the following simple method enables the factory operator to test the period of exposure in the machine3 ,start the machine full of water1 and after the same has become heated to the proper temperature1 change the inflow to full-cream milk1 continuing at the same rate4 ,note the exact time of change and also when first evidence of milkiness begins to appear at outflow4 ,if samples are taken from first appearance of milky condition and thereafter at different intervals for several minutes1 it is possible1 by determining the amount of butter-fat in the same1 to calculate with exactness how long it takes for the milk to entirely replace the water4 ,tests made by the writer#adc on the ,miller pasteurizer showed1 when fed at the rate of #a1gjj pounds per hour1 the minimum period of exposure to be #ae seconds1 and the maximum about #fj-gj seconds1 while about two-thirds of the milk passed the machine in #dj-ej seconds4 ,this manifest variation in the rate of flow of the milk through the machine is undoubtedly the reason why the results of this type of treatment are subject to so much variation4 ,naturally1 even a fatal temperature to bacterial life can be reduced to a point where actual destruction of even vegetating cells does not occur4 ,bacterial efficiency of reservoir pasteurizers4 ,the bacterial content of pasteurized milk and cream will depend somewhat on the number of organisms originally present in the same4 ,naturally1 if mixed milk brought to a creamery is pasteurized1 the number of organisms remaining after treatment would be greater than if the raw material was fresh and produced on a single farm4 ,an examination of milk and cream pasteurized on a commercial scale in the ,russell vat at the ,wisconsin ,dairy school showed that over #ii4h per cent of the bacterial life in raw milk or cream was destroyed by the heat employed1 i4 e41 #aee deg4 ,f4 for twenty minutes duration4#add ,in nearly one-half of the samples of milk1 the germ content in the pasteurized sample fell below #a1jjj bacteria per cc41 and the average of twenty-five samples contained #f1adj bacteria per cc4 ,in cream the germ content was higher1 averaging about #be1jjj bacteria per cc4 ,this milk was taken from the general creamery supply1 which was high in organisms1 containing on an average #c1fge1jjj bacteria per cc4 ,de ,schweinitz#ade has reported the germ content of a supply furnished in ,washington which was treated at #aeh deg4 to #afj deg4 ,f4 for fifteen minutes4 ,this supply came from a single source4 ,figures reported were from #dh-;hour-old agar plates4 ,undoubtedly these would have been higher if a longer period of incubation had been maintained4 ,the average of #hb samples1 taken for the period of one year1 showed #cbe bacteria per cc4 ,illustration3 ,,fig4 #bf4 ,effect of pasteurizing on germ content of milk4 ,black square represents bacteria of raw milk2 small white square1 those remaining after pasteurization4 ,bacterial efficiency of continuous-flow pasteurizers4 ,a quantitative determination of the bacteria found in milk and cream when treated in machinery of this class almost always shows a degree of variation in results that is not to be noted in the discontinuous apparatus4 ,illustration3 ,,fig4 #bg4 ,reid's ,continuous ,pasteurizer4 ,harding and ,rogers#adf have tested the efficiency of one of the ,danish type of continuous pasteurizers4 ,these experiments were made at #aeh deg41 #agf deg4 and #ahe deg4 ,f4 ,they found the efficiency of the machine not wholly satisfactory at the lower temperatures4 ,at #aeh deg4 ,f4 the average of fourteen tests gave #ae1cjj bacteria per cc41 with a maximum to minimum range from #fb1gij to #abj4 ,twenty-five examinations at #agf deg4 ,f4 showed an average of only #aag1 with a range from #cjj to #bj4 ,the results at #ahe deg4 ,f4 showed practically the same results as noted at #agf deg4 ,f4 ,considerable trouble was experienced with the scalding on of the milk to the walls of the machine when milk of high acidity was used4 ,jensen#adg details the results of #aci tests in #ahii1 made by the ,copenhagen ,health ,commission4 ,in #ff samples from one hundred thousand to one million organisms per cc4 were found1 and in #bb cases from one to five millions4 ,nineteen tests showed less than #aj1jjj per cc4 ,in a series of tests conducted by the writer#adh on a ,miller pasteurizer in commercial operation1 an average of #ba tests showed #ab1cej bacteria remaining in the milk when the milk was pasteurized from #aef deg4-#afd deg4 ,f4 ,the raw milk in these tests ran from #aae1jjj to about one million organisms per cc4 ,a recently devised machine of this type 7,pasteur7 has been tested by ,lehmann1 who found that it was necessary to heat the milk as high as #agf deg4 to #ahe deg4 ,f41 in order to secure satisfactory results on the bacterial content of the cream4 ,the writer tested ,reid's pasteurizer at #aee deg4 to #afe deg4 ,f4 with the following results3 in some cases as many as #dj per cent4 of the bacteria survived1 which number in some cases exceeded #b1jjj1jjj bacteria per cc4 ,pasteurizing details4 ,while the pasteurizing process is exceedingly simple1 yet1 in order to secure the best results1 certain conditions must be rigidly observed in the treatment before and after the heating process4 ,it is important to select the best possible milk for pasteurizing1 for if the milk has not been milked under clean conditions1 it is likely to be rich in the spore-bearing bacteria4 ,old milk1 or milk that has not been kept at a low temperature1 is much richer in germ-life than perfectly fresh or thoroughly chilled milk4 ,the true standard for selecting milk for pasteurization should be to determine the actual number of bacterial spores that are able to resist the heating process1 but this method is impracticable under commercial conditions4 ,the following method1 while only approximate in its results1 will be found helpful3 ,assuming that the age or treatment of the milk bears a certain relation to the presence of spores1 and that the acid increases in a general way with an increase in age or temperature1 the amount of acid present may be taken as an approximate index of the suitability of the milk for pasteurizing purposes4 ,biological tests were carried out in the author's laboratory#adi on milks having a high and low acid content1 and it was shown that the milk with the least acid was1 as a rule1 the freest from spore-bearing bacteria4 ,this acid determination can be made at the weigh-can by employing the ,farrington alkaline tablet which is used in cream-ripening4 ,where milk is pasteurized under general creamery conditions1 none should be used containing more than #j4b per cent acidity4 ,if only perfectly fresh milk is used1 the amount of acid will generally be about #j4ae per cent with phenolphthalein as indicator4 ,illustration3 ,,fig4 #bh4 ,diagram showing temperature changes in pasteurizing1 and the relation of same to bacterial growth4 ,shaded zone represents limits of bacterial growth1 #ej deg4-#aji deg4 ,f4 7#aj deg4-#dc deg4 ,c471 the intensity of shading indicating rapidity of development4 ,the solid black line shows temperature of milk during the process4 ,the necessity for rapid cooling is evident as the milk falls in temperature to that of growing zone4 ,emphasis has already been laid on the selection of a proper limit of pasteurizing 7p4 #aad74 ,it should be kept constantly in mind that the thermal death-point of any organism depends not alone on the temperature used1 but on the period of exposure4 ,with the lower limits given1 #adj deg4 ,f41 it is necessary to expose the milk for not less than fifteen minutes4 ,if a higher heat is employed 7and the cooked flavor disregarded7 the period of exposure may be curtailed4 ,chilling the milk4 ,it is very essential in pasteurizing that the heated milk be immediately chilled in order to prevent the germination of the resistant spores1 for if germination once occurs1 growth can go on at relatively low temperatures4 ,the following experiments by ,marshall#aej are of interest as showing the influence of refrigeration on germination of spores3 ,cultures of organisms that had been isolated from pasteurized milk were inoculated into bouillon4 ,one set was left to grow at room temperature1 another was pasteurized and allowed to stand at same temperature1 while another heated set was kept in a refrigerator4 ,the unheated cultures at room temperature showed evidence of growth in thirty trials in an average of #bf hours2 #bi heated cultures at room temperature all developed in an average of #ej hours1 while the heated cultures kept in refrigerator showed no growth in #de days with but four exceptions4 ,practically all of the rapid-process machines are provided with especially constructed cooling devices4 ,in some of them1 as in the ,miller and ,farrington1 the cooling is effected by passing the milk through two separate coolers that are constructed in the same general way as the heater4 ,with the first cooler1 cold running water is employed1 the temperature often being lowered in this way to #eh deg4 or #fj deg4 ,f4 ,further lessening of the temperature is secured by an additional ice water or brine cooler which brings the temperature down to #dj deg4-#ej deg4 ,f4 ,in the economical use of ice the ice itself should be applied as closely as possibly to the milk to be cooled1 for the larger part of the chilling value of ice comes from the melting of the same4 ,to convert a pound of ice at #cb deg4 ,f4 into a pound of water at the same temperature1 if we disregard radiation1 would require as much heat as would suffice to raise #adb pounds of water one degree ,f41 or one pound of water #adb deg4 ,f4 ,the absorptive capacity of milk for heat 7specific heat7 is not quite the same as it is with water1 being 4#hdg for milk in comparison with #a4j for water4#aea ,hot milk would therefore require somewhat less ice to cool it than would be required by any equal volume of water at the same temperature4 ,bottling the product4 ,if the milk has been properly pasteurized1 it should1 of course1 be dispensed in sterilized bottles4 ,glass bottles with plain pulp caps are best1 and these should be thoroughly sterilized in steam before using4 ,the bottling can best be done in a commercial bottling machine4 ,care must be taken to thoroughly clean this apparatus after use each day4 ,rubber valves in these machines suffer deterioration rapidly4 ,illustration3 ,,fig4 #bi4 ,relative consistency of pasteurized cream before 7,a7 and after 7,b7 treatment with viscogen as shown by rate of flow down inclined glass plate4 ,restoration of body of pasteurized cream4 ,the action of heat causes the tiny groupings of fat globules in normal milk 7,fig4 #bb7 to break up1 and with this change1 which occurs in the neighborhood of #adj deg4 ,f41 where the milk is heated for about #ae minutes and at about #afj-afe deg4 ,f4 where rapidly heated in a continuous stream1 the consistency of the liquid is diminished1 notwithstanding the fact that the fat-content remains unchanged4 ,babcock and the writer#aeb devised the following cure for this apparent defect4 ,if a strong solution of cane sugar is added to freshly slacked lime and the mixture allowed to stand1 a clear fluid can be decanted off4 ,the addition of this alkaline liquid1 which is called viscogen1 to pasteurized cream in proportions of about one part of sugar-lime solution to #ajj to #aej of cream1 restores the consistency of the cream1 as it causes the fat globules to cluster together in small groups4 ,the relative viscosity of creams can easily be determined by the following method 7,fig4 #bi73 ,take a perfectly clean piece of glass 7plate or picture glass is preferable1 as it is less liable to be wavy74 ,drop on one edge two or three drops of cream at intervals of an inch or so4 ,then incline piece of glass at such an angle as to cause the cream to flow down surface of glass4 ,the cream1 having the heavier body or viscosity1 will move more slowly4 ,if several samples of each cream are taken1 then the aggregate lengths of the different cream paths may be taken1 thereby eliminating slight differences due to condition of glass4 ,,footnotes3 #abf ,from #aj to #af cents per quart is usually paid for such milks4 #abg ,much improvement in quality could be made by more careful control of milk during shipment1 especially as to refrigeration2 also as to the care taken on the farms4 ,the use of the ordinary milking machine 7see page #cg71 would go far to reduce the germ content of milk4 #abh ,farrington1 ,journ4 ,amer4 ,chem4 ,soc41 ,sept41 #ahif4 #abi ,hite1 ,bull4 #eh1 ,west ,va4 ,expt4 ,stat41 #ahii4 #acj ,milch ,zeit41 #ahie1 ,no4 #i4 #aca ,ibid41 #ahig1 ,no4 #cc4 #acb ,bernstein1 ,milch ,zeit41 #ahid1 pp4 #ahd1 #bjj4 #acc ,thoerner1 ,chem4 ,zeit41 #ah3hde4 #acd ,snyder1 ,chemistry of ,dairying1 p4 #ei4 #ace ,doane and ,price 7,bull4 #gg1 ,md4 ,expt4 ,stat41 ,aug4 #aija7 give quite a full resume of the work on this subject in connection with rather extensive experiments made by them on feeding animals with raw1 pasteurized and sterilized milks4 #acf ,rickets is a disease in which the bones lack sufficient mineral matter to give them proper firmness4 ,marasmus is a condition in which the ingested food seems to fail to nourish the body and gradual wasting away occurs4 #acg ,de ,man1 ,arch4 f4 ,hyg41 #ahic1 #ah3acc4 #ach ,th4 ,smith1 ,journ4 of ,expt4 ,med41 #ahii1 #d3bag4 #aci ,russell and ,hastings1 #ag ,rept4 ,wis4 ,expt4 ,stat41 #aijj1 p4 #adg4 #adj ,russell and ,hastings1 #ba ,rept4 ,ibid41 #aijd4 #ada ,russell and ,hastings1 #ah ,rept4 ,ibid41 #aija4 #adb ,russell1 ,bull4 #dd1 ,wis4 ,expt4 ,stat4 #adc ,russell1 #bb ,wis4 ,expt4 ,stat4 ,rept41 #aije1 p4 #bcb4 #add ,russell1 #ab ,wis4 ,expt4 ,stat4 ,rept41 #ahie1 p4 #afj4 #ade ,de ,schweinitz1 ,nat4 ,med4 ,rev41 #ahii1 ,no4 #aa4 #adf ,harding and ,rogers4 ,bull4 #ahb1 ,n4 ,y4 7,geneva7 ,expt4 ,stat41 ,dec41 #ahii4 #adg ,jensen1 ,milchkunde und ,milch ,hygiene1 p4 #acb4 #adh #bb ,wis4 ,expt4 ,stat4 ,rept41 #aije1 p4 #bcf4 #adi ,shockley1 ,thesis1 ,univ4 of ,wis41 #ahif4 #aej ,marshall1 ,mich4 ,expt4 ,stat41 ,bull4 #adg1 p4 #dg4 #aea ,fleischmann1 ,landw4 ,versuchts ,stat41 #ag3bea4 #aeb ,babcock and ,russell1 ,bull4 #ed1 ,wis4 ,expt4 ,stat41 ,aug4 #ahif4 ,,chapter ,,vii4 ,,bacteria ,,and ,,butter-,,making4 ,in making butter from the butter fat in milk1 it is necessary to concentrate the fat globules into cream1 preliminary to the churning process4 ,the cream may be raised by the gravity process or separated from the milk by centrifugal action4 ,in either case the bacteria that are normally present in the milk differentiate themselves in varying numbers in the cream and the skim-milk4 ,the cream always contains per cc4 a great many more than the skim-milk1 the reason for this being that the bacteria are caught and held in the masses of fat globules1 which1 on account of their lighter specific gravity1 move toward the surface of the milk or toward the interior of the separator bowl4 ,this filtering action of the fat globules is similar to what happens in muddy water upon standing4 ,as the suspended particles fall to the bottom they carry with them a large number of the organisms that are in the liquid4 ,various creaming methods4 ,the creaming method has an important bearing on the kind as well as the number of the bacteria that are to be found in the cream4 ,the difference in species is largely determined by the difference in ripening temperature1 while the varying number is governed more by the age of the milk4 #a4 ,primitive gravity methods4 ,in the old shallow-pan process1 the temperature of the milk is relatively high1 as the milk is allowed to cool naturally4 ,this comparatively high temperature favors especially the development of those forms whose optimum growing-point is near the air temperature4 ,by this method the cream layer is exposed to the air for a longer time than with any other1 and consequently the contamination from this source is greater4 ,usually cream obtained by the shallow-pan process will contain a larger number of species and also have a higher acid content4 #b4 ,modern gravity methods4 ,in the ,cooley process1 or any of the modern gravity methods where cold water or ice is used to lower the temperature1 the conditions do not favor the growth of a large variety of species4 ,the number of bacteria in the cream will depend largely upon the manner in which the milk is handled previous to setting4 ,if care is used in milking1 and the milk is kept so as to exclude outside contamination1 the cream will be freer from bacteria than if carelessness prevails in handling the milk4 ,only those forms will develop in abundance that are able to grow at the low temperature at which the milk is set4 ,cream raised by this method is less frequently infected with undesirable forms than that which is creamed at a higher temperature4 #c4 ,centrifugal method4 ,separator cream should contain less germ-life than that which is secured in the old way4 ,it should contain only those forms that have found their way into the milk during and subsequent to the milking1 for the cream is ordinarily separated so soon that there is but little opportunity of infection1 if care is taken in the handling4 ,as a consequence1 the number of species found therein is smaller4 ,where milk is separated1 it is always prudent to cool the cream so as to check growth1 as the milk is generally heated before separating in order to skim efficiently4 ,although cream is numerically much richer in bacteria than milk1 yet the changes due to bacterial action are slower2 hence milk sours more rapidly than cream4 ,for this same reason1 cream will sour sooner when it remains on the milk than it will if it is separated as soon as possible4 ,this fact indicates the necessity of early creaming1 so as to increase the keeping quality of the product1 and is another argument in favor of the separator process4 ,ripening of cream4 ,if cream is allowed to remain at ordinary temperatures1 it undergoes a series of fermentation changes that are exceedingly complex in character1 the result of which is to produce in butter made from the same the characteristic flavor and aroma that are so well known in this article4 ,we are so accustomed to the development of these flavors in butter that they are not generally recognized as being intimately associated with bacterial activity unless compared with butter made from perfectly fresh cream4 ,sweet-cream butter lacks the aromatic principle that is prominent in the ripened product1 and while the flavor is delicate1 it is relatively unpronounced4 ,in the primitive method of butter-making1 where the butter was made on the farm1 the ripening of cream became a necessity in order that sufficient material might be accumulated to make a churning4 ,the ripening change occurred spontaneously without the exercise of any especial control4 ,with the development of the creamery system came the necessity of exercising a control of this process1 and therefore the modern butter-maker must understand the principles which are involved in this series of complex changes that largely give to his product its commercial value4 ,in these ripening changes three different factors are to be taken into consideration3 the development of acid1 flavor and aroma4 ,much confusion in the past has arisen from a failure to discriminate between these qualities4 ,while all three are produced simultaneously in ordinary ripening1 it does not necessarily follow that they are produced by the same cause4 ,if the ripening changes are allowed to go too far1 undesirable rather than beneficial decomposition products are produced4 ,these greatly impair the value of butter1 so that it becomes necessary to know just to what extent this process should be carried4 ,in cream ripening there is a very marked bacterial growth1 the extent of which is determined mainly by the temperature of the cream4 ,conn and ,esten#aec find that the number of organisms may vary widely in unripened cream1 but that the germ content of the ripened product is more uniform4 ,when cream is ready for the churn1 it often contains #ejj1jjj1jjj organisms per cc41 and frequently even a higher number4 ,this represents a germ content that has no parallel in any natural material4 ,the larger proportion of bacteria in cream as it is found in the creamery belong to the acid-producing class1 but in the process of ripening1 these forms seem to thrive still better1 so that when it is ready for churning the germ content of the cream is practically made up of this type4 ,effect on churning4 ,in fresh cream the fat globules which are suspended in the milk serum are surrounded by a film of albuminous material which prevents them from coalescing readily4 ,during the ripening changes1 this enveloping substance is modified1 probably by partial solution1 so that the globules cohere when agitated1 as in churning4 ,the result is that ripened cream churns more easily1 and as it is possible to cause a larger number of the smaller fat-globules to cohere to the butter granules1 the yield is slightly larger--a point of considerable economic importance where large quantities of butter are made4 ,development of acid4 ,the result of this enormous bacterial multiplication is that acid is produced in cream1 lactic being the principal acid so formed4 ,other organic acids are undoubtedly formed as well as certain aromatic products4 ,while the production of acid as a result of fermentative activity is usually accompanied with a development of flavor1 the flavor is not directly produced by the formation of acid4 ,if cream is treated in proper proportions with a commercial acid1 as hydrochloric1#aed it assumes the same churning properties as found in normally ripened cream1 but is devoid of the desired aromatic qualities4 ,lactic acid#aee has also been used in a similar way but with no better results4 ,the amount of acidity that should be developed under natural conditions so as to secure the optimum quality as to flavor and aroma is the most important question in cream ripening4 ,concerning this there have been two somewhat divergent views as to what is best in practice1 some holding that better results were obtained with cream ripened to a high degree of acidity than where a less amount was developed4#aef ,the present tendency seems to be to develop somewhat more than formerly1 as it is thought that this secures more of the high1 quick flavor wanted in the market4 ,on the average1 cream is ripened to about #j4e to #j4fe per cent4 acidity1 a higher percentage than this giving a strong-flavored butter4 ,in the determination of acidity1 the most convenient method is to employ the ,farrington alkaline tablet1 which permits of an accurate and rapid estimation of the acidity in the ripening cream4 ,the amount of acidity to be produced must of necessity be governed by the amount of butter-fat present1 for the formation of acid is confined to the serum of the cream2 consequently1 a rich cream would show less acid by titration than a thinner cream1 and still contain really as much acid as the other4 ,the importance of this factor is evident in gathered-cream factories4 ,the rate of ripening is dependent upon the conditions that affect the rate of growth of bacterial life1 such as time and temperature1 number of organisms in cream and also the per cent of butter fat in the cream4 ,some years ago it was customary to ripen cream at about #ej deg4 to #fj deg4 ,f41 but more recently better results have been obtained1 it is claimed1 where the ripening temperature is increased and the period of ripening lessened4 ,as high a temperature as #gj deg4 to #ge deg4 ,f4 has been recommended4 ,it should be said that this variation in practice may have a valid scientific foundation1 for the temperature of the ripening cream is undoubtedly the most potent factor in determining what kind of bacteria will develop most luxuriantly4 ,it is well known that those forms that are capable of producing bitter flavors are able to thrive better at a lower temperature than some of the desirable ripening species4 ,the importance of this factor would be lessened where a pure culture was used in pasteurized cream1 because here practically the selected organism alone controls the field4 ,it is frequently asserted that better results are obtained by stirring the cream and so exposing it to the air as much as possible4 ,experiments made at the ,ontario ,agricultural ,college1 however1 show practically no difference in the quality of the butter made by these two methods4 ,the great majority of the bacteria in the cream belong to the facultative class1 and are able to grow under conditions where they are not in direct contact with the air4 ,flavor and aroma4 ,the basis for the peculiar flavor or taste which ripened cream-butter possesses is due1 in large part1 to the formation of certain decomposition products formed by various bacteria4 ,aroma is a quality often confounded with flavor1 but this is produced by volatile products only1 which appeal to the sense of smell rather than taste4 ,generally a good flavor is accompanied by a desirable aroma1 but the origin of the two qualities is not necessarily dependent on the same organisms4 ,the quality of flavor and aroma in butter is1 of course1 also affected by other conditions1 as1 for instance1 the presence or absence of salt1 as well as the inherent qualities of the milk1 that are controlled1 to some extent at least1 by the character of the feed which is consumed by the animal4 ,the exact source of these desirable but evanescent qualities in butter is not yet satisfactorily determined4 ,according to ,storch1#aeg flavors are produced by the decomposition of the milk sugar and the absorption of the volatile flavors by the butter fat4 ,conn#aeh holds that the nitrogenous elements in cream serve as food for bacteria1 and in the decomposition of which the desired aromatic substance is produced4 ,the change is unquestionably a complex one1 and cannot be explained as a single fermentation4 ,there is no longer much doubt but that both acid-forming and casein-digesting species can take part in the production of proper flavors as well as desirable aromas4 ,the researches of ,conn1#aei who has studied this question most exhaustively1 indicate that both of these types of decomposition participate in the production of flavor and aroma4 ,he has shown that both flavor and aroma production are independent of acid2 that many good flavor-producing forms belong to that class which renders milk alkaline1 or do not change the reaction at all4 ,some of these species liquefied gelatin and would therefore belong to the casein-dissolving class4 ,those species that produced bad flavors are also included in both fermentative types4 ,conn has found a number of organisms that are favorable flavor-producers2 in fact they were much more numerous than desirable aroma-yielding species4 ,none of the favorable aroma forms according to his investigations were lactic-acid species1--a view which is also shared by ,weigmann4#afj ,mc,donnell#afa has found that the production of aroma in certain cases varies at different temperatures1 the most pronounced being evolved near the optimum growing temperature1 which1 as a general rule1 is too high for cream ripening4 ,the majority of bacteria in ripening cream do not seem to exert any marked influence in butter4 ,a considerable number of species are positively beneficial1 inasmuch as they produce a good flavor or aroma4 ,a more limited number are concerned in the production of undesirable ripening changes4 ,this condition being true1 it may seem strange that butter is as good as it is1 because so frequently the requisite care is not given to the development of proper ripening4 ,in all probability the chief reason why this is so is that those bacteria that find milk and cream pre-eminently suited to their development1 e4 g4 the lactic-acid class1 are either neutral or beneficial in their effect on butter4 ,use of starters4 ,experience has amply demonstrated that it is possible to control the nature of the fermentative changes that occur in ripening cream to such an extent as to materially improve the quality of the butter4 ,this is frequently done by the addition of a starter4 ,while starters have been employed for many years for the purpose mentioned1 it is only recently that their nature has been understood4 ,a starter may be selected from widely divergent sources1 but in all cases it is sure to contain a large number of bacteria1 and the presumption is that they are of such a nature as to produce desirable fermentative changes in the cream4 ,in the selection of these so-called natural starters1 it follows that they must be chosen under such conditions as experience has shown to give favorable results4 ,for this purpose1 whole milk from a single animal is often used where the same is observed to sour with the production of no gas or other undesirable taint4 ,a skim-milk starter from a mixed supply is recommended by many4 ,butter milk is frequently employed1 but in the opinion of butter experts is not as suitable as the others mentioned4 ,it not infrequently happens that the practical operator may be misled in selecting a starter that is not desirable1 or by continuing its use after it has become contaminated4 ,in #ahijafb a new system of cream ripening was introduced in ,denmark by ,storch that possesses the merit of being a truly scientific and at the same time practical method4 ,this consisted in the use of pure cultures of specific organisms that were selected on account of their ability to produce a desirable ripening change in cream4 ,the introduction of these so-called culture starters has become universal in ,denmark1 and in parts of ,germany4 ,their use is also rapidly extending in this country1 ,australia and ,new ,zealand4 ,principles of pure-culture cream-ripening4 ,in the proper use of pure cultures for ripening cream1 it is necessary first to eliminate as far as possible the bacteria already present in cream before the culture starter is added4 ,this result is accomplished by heating the cream to a temperature sufficiently high to destroy the vegetating organisms4 ,the addition of a properly selected starter will then give the chosen organism such an impetus as will generally enable it to gain the ascendency over any other bacteria and so control the character of the ripening4 ,the principle employed is quite like that practiced in raising grain4 ,the farmer prepares his soil by plowing1 in this way killing the weeds4 ,then he sows his selected grain1 which is merely a pure culture1 and by the rapid growth of this1 other forms are held in check4 ,the attempt has been made to use these culture starters in raw sweet cream1 but it can scarcely be expected that the most beneficial results will be attained in this way4 ,this method has been justified on the basis of the following experiments4 ,where cream is pasteurized and no starter is added1 the spore-bearing forms frequently produce undesirable flavors4 ,these can almost always be controlled if a culture starter is added1 the obnoxious form being repressed by the presence of the added starter4 ,this condition is interpreted as indicating that the addition of a starter to cream which already contains developing bacteria will prevent those originally present in the cream from growing4#afc ,this repressive action of one species on another is a well-known bacteriological fact1 but it must be remembered that such an explanation is only applicable in those cases where the culture organism is better able to develop than those forms that already exist in the cream4 ,if the culture organism is added to raw milk or cream which already contains a flora that is well suited to develop in this medium1 it is quite doubtful whether it would gain the supremacy in the ripening cream4 ,the above method of adding a culture to raw cream renders cream-ripening details less burdensome1 but at the same time ,danish experience1 which is entitled to most credence on this question1 is opposed to this method4 ,reputed advantages of culture starters4 #a4 ,flavor and aroma4 ,naturally the flavor produced by pure-culture ferments depends upon the character of the organism used4 ,those which are most extensively used are able to produce a perfectly clean but mild flavor1 and a delicate but not pronounced aroma4 ,the high1 quick flavor and aroma that is so much desired in the ,american market is not readily obtained by the use of cultures4 ,it is quite problematical whether the use of any single species will give any more marked aroma than normally occurs in natural ripening4 #b4 ,uniformity of product4 ,culture starters produce a more uniform product because the type of fermentation is under more complete control1 and herein is the greatest advantage to be derived from their use4 ,even the best butter-maker at times will fail to secure uniform results if his starter is not perfectly satisfactory4 #c4 ,keeping quality of product4 ,butter made from pasteurized cream to which a pure-culture starter has been added will keep much better than the ordinary product1 because the diversity of the bacterial flora is less and the milk is therefore not so likely to contain those organisms that produce an off condition4 #d4 ,elimination of taints4 ,many defective conditions in butter are attributable to the growth of undesirable bacteria in the cream that result in the formation of off flavors and taints4 ,if cream is pasteurized1 thereby destroying these organisms1 then ripened with pure ferments1 it is generally possible to eliminate the abnormal conditions4#afd ,taints may also be present in cream due to direct absorption from the cow or through exposure to foul odors4#afe ,troubles of this sort may thus be carried over to the butter4 ,this is particularly true in regions where leeks and wild onions abound1 as in some of the ,atlantic ,states4 ,the heating of the cream tends to expel these volatile taints1 so that a fairly good article of butter can be made from what would otherwise be a relatively worthless product4 ,characteristics desired in culture starters4 ,certain conditions as the following are desirable in starters made from pure cultures3 #a4 ,vigorous growth in milk at ordinary ripening temperatures4 #b4 ,ability to form acid so as to facilitate churning and increase the yield of butter4 #c4 ,able to produce a clean flavor and desirable aroma4 #d4 ,impart a good keeping quality to butter4 #e4 ,not easily modified in its flavor-producing qualities by artificial cultivation4 ,these different conditions are difficult to attain1 for the reason that some of them seem to be in part incompatible4 ,weigmann#aff found that a good aroma was generally an evanescent property1 and therefore opposed to good keeping quality4 ,conn has shown that the functions of acid-formation1 flavor and aroma production are not necessarily related1 and therefore the chances of finding a single organism that possesses all the desirable attributes are not very good4 ,in all probability no one germ possesses all of these desirable qualities1 but natural ripening is the resultant of the action of several forms4#afg ,this idea has led to the attempt at mixing selected organisms that have been chosen on account of certain favorable characteristics which they might possess4 ,the difficulty of maintaining such a composite culture in its correct proportions when it is propagated in the creamery is seemingly well nigh insuperable1 as one organism is very apt to develop more or less rapidly than the other4 ,a very satisfactory way in which these cultures are marketed is to mix the bacterial growth with some sterile1 inert1 dry substance4 ,this is the method used in most of the ,danish cultures4 ,in this country1 some of the more prominent cultures employed are marketed in a liquid form4 ,culture vs4 home-made starters4 ,one great advantage which has accrued from the use of culture or commercial starters has been that in emphasizing the need of closer control of the ripening process1 greater attention has been paid to the carrying out of the details4 ,in the hands of the better operators1 the differences in flavor of butter made with a culture or a natural starter are not marked1#afh but in the hands of those who fail to make a good product under ordinary conditions1 an improvement is often secured where a commercial culture is used4 ,pasteurization as applied to butter-making4 ,this process1 as applied to butter making1 is often confounded with the treatment of milk and cream for direct consumption4 ,it is unfortunate that the same term is used in connection with the two methods1 for they have but little in common except in the use of heat to destroy the germ life of the milk4 ,in pasteurizing cream for butter-making1 it is not necessary to observe the stringent precautions that are to be noted in the preservation of milk2 for the addition of a rapidly developing starter controls at once the fermentative changes that subsequently occur4 ,then again1 the physical requirement as to the production of a cooked taste is not so stringent in butter-making4 ,while a cooked taste is imparted to milk or even cream at about #aeh deg4 ,f41 it is possible to make butter that shows no permanent cooked taste from cream that has been raised as high as #ahe deg4 or even #aie deg4 ,f4 ,this is due to the fact that the fat does not readily take up those substances that give to scalded milk its peculiar flavor4 ,unless care is taken in the manipulation of the heated cream1 the grain or body of the butter may be injured4 ,this tendency can be overcome if the ripened cream is chilled to #dh deg4 ,f4 for about two hours before churning4 ,it is also essential that the heated cream should be quickly and thoroughly chilled after being pasteurized4 ,the ,danes1 who were the first to employ pasteurization in butter-making1 used1 in the beginning1 a temperature ranging from #aeh deg4 to #afg deg4 ,f41 but owing to the prevalence of such diseases as tuberculosis and foot-and-mouth disease1 it became necessary to treat all of the skim milk that was returned from the creameries4 ,for this purpose the skim milk is heated to a temperature of #agf deg4 ,f41 it having been more recently determined that this degree of heat is sufficient to destroy the seeds of disease4 ,with the use of this higher temperature the capacity of the pasteurizing apparatus is considerably reduced1 but the higher temperature is rendered necessary by the prevailing conditions as to disease4 ,when the system was first introduced in ,denmark1 two methods of procedure were followed3 the whole milk was heated to a sufficiently high temperature to thoroughly pasteurize it before it was separated1 or it was separated first1 and the cream pasteurized afterwards4 ,in the latter case1 it is necessary to heat the skim milk after separation to destroy the disease organisms1 but this can be quickly done by the use of steam directly4 ,much more care must be used in heating the cream in order to prevent injury to the grain of the butter4 ,in spite of the extra trouble of heating the cream and skim milk separately1 this method has practically supplanted the single heating4 ,with the continual spread of tuberculosis in ,america the heating of skim milk separately is beginning to be introduced4#afi ,use of starters in pasteurized and unpasteurized cream4 ,in order to secure the beneficial results presumably attributable to the use of a starter1 natural as well as a pure culture1 it should be employed in cream in which the bacteria have first been killed out by pasteurization4 ,this is certainly the most logical and scientific method and is the way in which the process has been developed in ,denmark4 ,here in this country1 the use of pure cultures has been quite rapidly extended1 but the system of heating the cream has been used in only a slight measure4 ,the increased labor and expense incurred in pasteurizing the cream has naturally militated somewhat against the wide-spread use of the process1 but doubtless the main factor has been the inability to secure as high a flavor where the cream was heated as in the unheated product4 ,as the demands of the market change from a high1 quick flavor to one that is somewhat milder but of better keeping quality1 doubtless pasteurization of the cream will become more and more popular4 ,that such a change is gradually occurring is already evident1 although as yet only a small proportion of butter made in this country is now made in this way4 ,where the cream is unheated1 a considerable number of species will be found1 and even the addition of a pure culture1 if that culture is of the lactic acid-producing species1 will to some extent control the type of fermentation that occurs4 ,such would not be the case with a culture composed of the casein-digesting type of bacteria4 ,only those forms could thus be used which are especially well suited to development in raw cream4 ,for this reason the pure culture ferments that are generally employed in creamery practice are organisms of the lactic acid type1 able to grow rapidly in cream and produce a pure cream flavor in the butter4 ,purity of commercial starters4 ,naturally the butter maker is forced to rely on the laboratory for his commercial starter1 and the question will often arise as to the purity and vigor of the various ferments employed4 ,as there is no way for the factory operator to ascertain the actual condition of the starter1 except by using the same1 the greatest care should be taken by the manufacturer to insure the absolute purity of the seed used4 ,a bacteriological examination of the various cultures which have been placed on the market not infrequently reveals an impure condition4 ,in several cases the writer has found a not inconsiderable number of liquefying bacteria mixed with the selected organism4 ,molds not infrequently are found in cultures put up in the dry form4 ,doubtless the effect of these accidental contaminations is considerably less in the case of a starter composed of a distinctively lactic acid-producing organism than with a form which is less capable of thriving vigorously in milk1 and it should be said that these impurities can frequently be eliminated by continued propagation4 ,the virility and vigor of the starter is also a fluctuating factor1 dependent in part at least1 upon the conditions under which the organism is grown4 ,in some cases the germ is cultivated in solutions in which acid cannot be formed in abundance4 ,where the conditions permit of the formation of acid1 as would be the case if sugar was present with a lactic acid-producing species1 the vitality of the culture is often impaired by the action of the gradually accumulating acid4 ,some manufacturers attempt to minimize this deleterious condition by adding carbonate of lime which unites with the acid that is formed4 ,propagation of starters for cream-ripening4 ,the preparation and propagation of a starter for cream-ripening is a process involving considerable bacteriological knowledge1 whether the starter is of domestic origin or prepared from a pure-culture ferment4 ,in any event1 it is necessary that the starter should be handled in a way so as to prevent the introduction of foreign bacteria as far as possible4 ,it should be remembered at all times that the starter is a live thing and must be handled throughout its entire history in a way so as to retain its vitality and vigor unimpaired4 ,the following points should be taken into consideration in growing the starter and transferring it from day to day3 #a4 ,if a commercial starter is used1 see that it is fresh and that the seal has not been broken4 ,if the culture is too old1 the larger part of the organisms may have died out before it is transferred1 in which case the effect of its addition to the sterilized milk would be of little value4 ,when the commercial ferment is received1 it should be stored in the refrigerator pending its use so as to retard as much as possible the changes that naturally go on in the culture liquid4 ,be careful that the bottle is not exposed to the influence of direct sunlight for in a transparent medium the organisms may be readily killed by the disinfecting action of the sun's rays4 #b4 ,if a home-made starter is employed1 use the greatest possible care in selecting the milk that is to be used as a basis for the starter4 #c4 ,for the propagation and perpetuation of the starter from day to day1 it is necessary that the same should be grown in milk that is as germ-free as it is possible to secure it4 ,for this purpose sterilize some fresh skim-milk in a covered can that has previously been well steamed4 ,this can be done easily by setting cans containing skim-milk in a vat filled with water and heating the same to #ahj deg4 ,f4 or above for one-half hour or more4 ,steam should not be introduced directly4 ,this process destroys all but a few of the most resistant spore-bearing organisms4 ,this will give a cooked flavor to the milk1 but will not affect the cream to which the starter is added4 ,dairy supply houses are now introducing the use of starter cans that are specially made for this purpose4 #d4 ,after the heated milk is cooled down to about #gj deg4 or #hj deg4 ,f41 it can be inoculated with the desired culture4 ,sometimes it is desirable to build up the starter by propagating it first in a smaller volume of milk1 and then after this has developed1 adding it to a larger amount4 ,this method is of particular value where a large amount of starter is needed for the cream-ripening4 #e4 ,after the milk has been inoculated1 it should be kept at a temperature that is suitable for the rapid development of the contained bacteria1 #fe deg4-#ge deg4 ,f41 which temperature should be kept as uniform as possible4 ,this can best be done by setting the covered can in a vat filled with warm water4 ,the starter cans are often arranged so that temperature can be controlled by circulating water4 #f4 ,the starter should not be too thoroughly curdled when it is needed for use1 but should be well soured and only partially curdled for it is difficult to break up thoroughly the curd particles if the starter is completely curdled4 ,if these curd masses are added to ripening cream1 white specks may appear in the butter4 #g4 ,the vigor of the starter is in all probability stronger when the milk is on the point of curdling than it is after the curd has been formed some time4 ,the continued formation of lactic acid kills many of the bacteria and thus weakens the fermentative action4 ,it is therefore highly important that the acidity of the starter should be closely watched4 #h4 ,do not refrigerate the starter when it has reached the proper stage of development1 as this retards the bacterial growth in the same manner as cold weather checks the growth of grain4 ,it is preferable to dilute the starter1 if it cannot be used when ready1 with sufficient freshly sterilized sweet milk to hold the acidity at the proper point and thus keep the bacteria in the starter in a condition which will favor vigorous growth4 #i4 ,the starter should be propagated from day to day by adding a small quantity to a new lot of freshly prepared milk4 ,for this purpose two propagating cans should be provided so that one starter may be in use while the other is being prepared4 ,how long should a starter be propagated8 ,no hard-and-fast rule can be given for this1 for it depends largely upon how carefully the starter is handled during its propagation4 ,if the starter is grown in sterilized milk kept in steamed vessels and is handled with sterile dippers1 it is possible to maintain it in a state of relative purity for a considerable period of time2 if1 however1 no especial care is given1 it will soon become infected by the air1 and the retention of its purity will depend more upon the ability of the contained organism to choke out foreign growths than upon any other factor4 ,experience seems to indicate that pure-culture starters run out sooner than domestic starters4 ,while it is possible1 by bacteriological methods1 to determine with accuracy the actual condition of a starter as to its germ content1 still such methods are inapplicable in creamery practice4 ,here the maker must rely largely upon the general appearance of the starter as determined by taste and smell4 ,the supply houses that deal in cultures of this class generally expect to supply a new culture at least every month4 ,bacteria in butter4 ,as ripened cream is necessarily rich in bacteria1 it follows that butter will also contain germ life in varying amounts1 but as butter-fat is not well adapted for bacterial food1 the number of germs in butter is usually less than in ripened cream4 ,sweet-cream butter is naturally poorer in germ life than that made from ripened cream4 ,grotenfelt reports in sweet-cream butter1 the so-called ,paris butter1 only a few bacteria while in acid cream butter the germ content runs from scores to hundreds of thousands4 ,effect of bacteria in wash water4 ,an important factor in contamination may be the wash water that is used4 ,much carelessness often prevails regarding the location and drainage of the creamery well1 and if same becomes polluted with organic matter1 bacterial growth goes on apace4 ,melick#agj has made some interesting studies on using pasteurized and sterilized well waters for washing4 ,he found a direct relation to exist between the bacterial content of the wash water and the keeping quality of the butter4 ,some creameries have tried filtered water but under ordinary conditions a filter1 unless it is tended to with great regularity1 becomes a source of infection rather than otherwise4 ,changes in germ content4 ,the bacteria that are incorporated with the butter as it first comes undergo a slight increase for the first few days4 ,the duration of this period of increase is dependent largely upon the condition of the butter4 ,if the buttermilk is well worked out of the butter1 the increase is slight and lasts for a few days only1 while the presence of so nutritious a medium as buttermilk affords conditions much more favorable for the continued growth of the organisms4 ,while there may be many varieties in butter when it is fresh1 they are very soon reduced in kind as well as number4 ,the lactic acid group of organisms disappear quite rapidly2 the spore-bearing species remaining for a somewhat longer time4 ,butter examined after it is several months old is often found to be almost free from germs4 ,in the manufacture of butter there is much that is dependent upon the mechanical processes of churning1 washing1 salting and working the product4 ,these processes do not involve any bacteriological principles other than those that are incident to cleanliness4 ,the cream1 if ripened properly1 will contain such enormous numbers of favorable forms that the access of the few organisms that are derived from the churn1 the air1 or the water in washing will have little effect1 unless the conditions are abnormal4 ,,bacterial ,,defects ,,in ,,butter4 ,rancid change in butter4 ,fresh butter has a peculiar aroma that is very desirable and one that enhances the market price1 if it can be retained2 but this delicate flavor is more or less evanescent1 soon disappearing1 even in the best makes4 ,while a good butter loses with age some of the peculiar aroma that it possesses when first made1 yet a gilt-edged product should retain its good keeping qualities for some length of time4 ,all butters1 however1 sooner or later undergo a change that renders them worthless for table use4 ,this change is usually a rancidity that is observed in all stale products of this class4 ,the cause of this rancid condition in butter was at first attributed to the formation of butyric acid1 but it is now recognized that other changes also enter in4#aga ,light and especially air also exert a marked effect on the flavor of butter4 ,where butter is kept in small packages it is much more prone to develop off flavors than when packed in large tubs4 ,from the carefully executed experiments of ,jensen it appears that some of the molds as well as certain species of bacteria are able to incite these changes4 ,these organisms are common in the air and water and it therefore readily follows that inoculation occurs4 ,practically1 rancidity is held in check by storing butter at low temperatures where germ growth is quite suspended4 ,lack of flavor4 ,often this may be due to improper handling of the cream in not allowing it to ripen far enough1 but sometimes it is impossible to produce a high flavor4 ,the lack of flavor in this case is due to the absence of the proper flavor-producing organisms4 ,this condition can usually be overcome by the addition of a proper starter4 ,putrid butter4 ,this specific butter trouble has been observed in ,denmark1 where it has been studied by ,jensen4#agb ,butter affected by it rapidly acquires a peculiar putrid odor that ruins it for table use4 ,sometimes1 this flavor may be developed in the cream previous to churning4 ,jensen found the trouble to be due to several different putrefactive bacteria4 ,one form which he called ,bacillus foetidus lactis1 a close ally of the common feces bacillus1 produced this rotten odor and taste in milk in a very short time4 ,fortunately1 this organism was easily killed by a comparatively low heat1 so that pasteurization of the cream and use of a culture starter quickly eliminated the trouble1 where it was tried4 ,turnip-flavored butter4 ,butter sometimes acquires a peculiar flavor recalling the order of turnips1 rutabagas1 and other root crops4 ,often this trouble is due to feeding1 there being in several of these crops1 aromatic substances that pass directly into the milk1 but in some instances the trouble arises from bacteria that are able to produce decomposition products1#agc the odor and taste of which strongly recalls these vegetables4 ,cowy butter4 ,frequently there is to be noted in milk a peculiar odor that resembles that of the cow stable4 ,usually this defect in milk has been ascribed to the absorption of impure gases by the milk as it cools1 although the gases and odors naturally present in fresh milk have this peculiar property that is demonstrable by certain methods of aeration4 ,occasionally it is transmitted to butter1 and recently ,pammel#agd has isolated from butter a bacillus that produced in milk the same peculiar odor so commonly present in stables4 ,lardy and tallowy butter4 ,the presence of this unpleasant taste in butter may be due to a variety of causes4 ,in some instances1 improper food seems to be the source of the trouble2 then again1 butter exposed to direct sunlight bleaches in color and develops a lardy flavor4#age ,in addition to these1 cases have been found in which the defect has been traced to the action of bacteria4 ,storch#agf has described a lactic-acid form in a sample of tallowy butter that was able to produce this disagreeable odor4 ,oily butter4 ,jensen has isolated one of the causes of the dreaded oily butter that is reported quite frequently in ,denmark4 ,the specific organism that he found belongs to the sour-milk bacteria4 ,in twenty-four hours it curdles milk1 the curd being solid like that of ordinary sour milk4 ,there is produced1 however1 in addition to this1 an unpleasant odor and taste resembling that of machine oil1 a peculiarity that is transmitted directly to butter made from affected cream4 ,bitter butter4 ,now and then butter develops a bitter taste that may be due to a variety of different bacterial forms4 ,in most cases1 the bitter flavor in the butter is derived primarily from the bacteria present in the cream or milk4 ,several of the fermentations of this character in milk are also to be found in butter4 ,in addition to these defects produced by a biological cause1 bitter flavors in butter are sometimes produced by the milk being impregnated with volatile1 bitter substances derived from weeds4 ,moldy butter4 ,this defect is perhaps the most serious because most common4 ,it is produced by the development of a number of different varieties of molds4 ,the trouble appears most frequently in packed butter on the outside of the mass of butter in contact with the tub4 ,mold spores are so widely disseminated that if proper conditions are given for their germination1 they are almost sure to develop4 ,in some cases the mold is due to the growth of the ordinary bread mold1 ,penicillium glaucum2 in other cases a black mold develops1 due often to ,cladosporium butyri4 ,not infrequently trouble of this character is associated with the use of parchment wrappers4 ,the difficulty can easily be held in check by soaking the parchment linings and the tubs in a strong brine1 or paraffining the inside of the tub4 ,fishy butter4 ,considerable trouble has been experienced in ,australian butter exported to ,europe in which a fishy flavor developed4 ,it was noted that the production of this defect seemed to be dependent upon the storage temperature at which the butter was kept4 ,when the butter was refrigerated at #ae deg4 ,f4 no further difficulty was experienced4 ,it is claimed that the cause of this condition is due to the formation of trimethylamine 7herring brine odor7 due to the growth of the mold fungus ,oidium lactis1 developing in combination with the lactic-acid bacteria4 ,a fishy taste is sometimes noted in canned butter4 ,rogers#agg has determined that this flavor is caused by yeasts 7,torula7 which produce fat-splitting enzyms capable of producing this undesirable change4 ,,footnotes3 #aec ,conn and ,esten1 ,cent4 f4 ,bakt41 ,,ii ,abt41 #aija1 #g3gdf4 #aed ,tiemann1 ,milch ,zeit41 #bc3gja4 #aee ,milch ,zeit41 #ahhi1 p4 #g2 #ahid1 p4 #fbd2 #ahie1 p4 #chc4 #aef ,dean1 ,ont4 ,agr4 ,coll41 #ahig1 p4 #ff4 #aeg ,storch1 ,nogle1 ,unders4 over ,floed4 ,syrning1 #ahij4 #aeh ,conn1 #f ,storrs ,expt4 ,stat41 #ahic1 p4 #ff4 #aei ,conn1 #i ,storrs ,expt4 ,stat41 #ahif1 p4 #ag4 #afj ,weigmann1 ,milch ,zeit41 #ahia1 p4 #gic #afa ,mc,donnell1 ue4 ,milchsaeure ,bakterien 7,diss4 ,kiel1 #ahii71 p4 #dc4 #afb ,storch1 ,milch ,zeit41 #ahij1 p4 #cjd4 #afc ,conn1 #i ,storrs ,expt4 ,stat41 #ahif1 p4 #be4 #afd ,milch ,zeit41 #ahia1 p4 #abb2 #ahid1 p4 #bhd2 #ahie1 p4 #ef2 #ahif1 p4 #afc4 #afe ,mc,kay1 ,bull4 #cb1 ,iowa ,expt4 ,stat41 p4 #dg #aff ,weigmann1 ,landw4 ,woch4 f4 ,schl4 ,hol41 ,no4 #b1 #ahij4 #afg ,weigmann1 ,cent4 f4 ,bakt41 ,,ii ,abt41 #c3dig1 #ahig4 #afh ,at the ,national ,creamery ,buttermakers' ,association for #aija1 #aic out of #bdj exhibitors used starters4 ,of those that employed starters1 nearly one-half used commercial cultures4 ,there was practically no difference in the average score of the two classes of starters1 but those using starters ranked nearly two points higher in flavor than those that did not4 #afi ,russell1 ,bull4 #adc1 ,wis4 ,expt4 ,stat41 ,feb4 #aijg4 #agj ,melick1 ,bull4 #ach1 ,kansas ,expt4 ,stat41 ,june #aijf4 #aga ,reinmann1 ,cent4 f4 ,bakt41 #aijj1 #f3aca2 ,jensen1 ,landw4 ,jahr4 d4 ,schweiz1 #aija4 #agb ,jensen1 ,cent4 f4 ,bakt41 #ahia1 #aa3dji4 #agc ,jensen1 ,milch ,zeit41 #ahib1 #f1 ,nos4 #e and #f4 #agd ,pammel1 ,bull4 #ba1 ,iowa ,expt4 ,stat41 p4 #hjc4 #age ,fischer1 ,hyg4 ,rund41 #e3egc4 #agf ,storch1 #ah ,rept4 ,danish ,agric4 ,expt4 ,stat41 #ahij4 #agg ,rogers ,bull4 #eg1 ,b4 ,a4 ,i4 ,u4 ,s4 ,dept ,agric41 #aijd4 ,,chapter ,,viii4 ,,bacteria ,,in ,,cheese4 ,the art of cheese-making1 like all other phases of dairying1 has been developed mainly as a result of empirical methods4 ,within the last decade or so1 the subject has received more attention from the scientific point of view and the underlying causes determined to some extent4 ,since the subject has been investigated from the bacteriological point of view1 much light has been thrown on the cause of many changes that were heretofore inexplicable4 ,our knowledge1 as yet1 is quite meager1 but enough has already been determined to indicate that the whole industry is largely based on the phenomena of ferment action1 and that the application of bacteriological principles and ideas is sure to yield more than ordinary results1 in explaining1 in a rational way1 the reasons underlying many of the processes to be observed in this industry4 ,the problem of good milk is a vital one in any phase of dairy activity1 but it is pre-eminently so in cheese-making1 for the ability to make a first-class product depends to a large extent on the quality of the raw material4 ,cheese contains so large a proportion of nitrogenous constituents that it is admirably suited1 as a food medium1 to the development of bacteria2 much better1 in fact1 than butter4 ,,influence ,,of ,,bacteria ,,in ,,normal ,,cheese ,,processes4 ,in the manufacture of cheddar cheese bacteria exert a marked influence in the initial stages of the process4 ,to produce the proper texture that characterizes cheddar cheese1 it is necessary to develop a certain amount of acid which acts upon the casein4 ,this acidity is measured by the development of the lactic-acid bacteria that normally abound in the milk2 or1 as the cheese-maker expresses it1 the milk is ripened to the proper point4 ,the action of the rennet1 which is added to precipitate the casein of the milk1 is markedly affected by the amount of acid present1 as well as the temperature4 ,hence it is desirable to have a standard amount of acidity as well as a standard temperature for coagulation1 so as to unify conditions4 ,it frequently happens that the milk is abnormal with reference to its bacterial content1 on account of the absence of the proper lactic bacteria1 or the presence of forms capable of producing fermentative changes of an undesirable character4 ,in such cases the maker attempts to overcome the effect of the unwelcome bacteria by adding a starter2 or he must vary his method of manufacture to some extent to meet these new conditions4 ,use of starters4 ,a starter may be employed to hasten the ripening of milk that is extremely sweet1 so as to curtail the time necessary to get the cheese to press2 or it may be used to overcome the effect of abnormal conditions4 ,the starter that is employed is generally one of domestic origin1 and is usually taken from skim milk that has been allowed to ferment and sour under carefully controlled conditions4 ,of course much depends upon the quality of the starter1 and in a natural starter there is always the possibility that it may not be perfectly pure4 ,within recent years the attempt has been made to control the effect of the starter more thoroughly by using pure cultures of some desirable lactic-acid form4#agh ,this has rendered the making of cheese not only more uniform1 but has aided in repressing abnormal fermentations particularly those that are characterized by the production of gas4 ,recently1 pure cultures of ,adametz's ,b4 nobilis1 a digesting organism that is claimed to be the cause of the breaking down of the casein and also of the peculiar aroma of ,emmenthaler cheese1 has been placed on the market under the name ,tyrogen4 ,it is claimed that the use of this starter1 which is added directly to the milk and also rubbed on the surface of the cheese1 results in the improvement of the curds1 assists in the development of the proper holes1 imparts a favorable aroma and hastens ripening4#agi ,campbell#ahj states that the discoloration of cheese in ,england1 which is due to the formation of white spots that are produced by the bleaching of the coloring matter in the cheese1 may be overcome by the use of lactic-acid starters4 ,the use of stringy or slimy whey has been advocated in ,holland for some years as a means of overcoming the tendency toward gas formation in ,edam cheese which is made from practically sweet milk4 ,this fermentation1 the essential feature of which is produced by a culture of ,streptococcus ,hollandicus1#aha develops acid in a marked degree1 thereby inhibiting the production of gas4 ,the use of masses of moldy bread in directing the fermentation of ,roquefort cheese is another illustration of the empirical development of starters1 although in this instance it is added after the curds have been prepared for the press4 ,pasteurizing milk for cheese-making4 ,if it were possible to use properly pasteurized milk in cheese-making1 then practically all abnormal conditions could be controlled by the use of properly selected starters4 ,numerous attempts have been made to perfect this system with reference to cheddar cheese1 but so far they have been attended with imperfect success4 ,the reason for this is that in pasteurizing milk1 the soluble lime salts are precipitated by the action of heat1 and under these conditions rennet extract does not curdle the casein in a normal manner4 ,this condition can be restored1 in part at least1 by the addition of soluble lime salts1 such as calcium chlorid2 but in our experience1 desirable results were not obtained where heated milks to which this calcium solution had been added were made into cheddar cheese4 ,considerable experience has been gained in the use of heated milks in the manufacture of certain types of foreign cheese4 ,klein#ahb finds that ,brick cheese can be successfully made even where the milk is heated as high as #ahe deg4 ,f4 ,an increased weight is secured by the addition of the coagulated albumin and also increased moisture4 ,bacteria in rennet4 ,in the use of natural rennets1 such as are frequently employed in the making of ,swiss cheese1 considerable numbers of bacteria are added to the milk4 ,although these rennets are preserved in salt1 alcohol or boric acid1 they are never free from bacteria4 ,adametz#ahc found ten different species and from #fdj1jjj to #ijj1jjj bacteria per cc4 in natural rennets4 ,freudenreich has shown that rennet extract solutions can be used in ,swiss cheese-making quite as well as natural rennets2 but to secure the best results1 a small quantity of pure lactic ferment must be added to simulate the conditions that prevail when natural rennets are soaked in whey1 which1 it must be remembered1 is a fluid rich in bacterial life4 ,where rennet extract or tablets are used1 as is generally the case in cheddar making1 the number of bacteria added is so infinitesimal as to be negligible4 ,development of acid4 ,in the manufacture of cheddar cheese1 the development of acid exerts an important influence on the character of the product4 ,this is brought about by holding the curds at temperatures favorable to the growth of the bacteria in the same4 ,under these conditions the lactic-acid organisms1 which usually predominate1 develop very rapidly1 producing thereby considerable quantities of acid which change materially the texture of the curds4 ,the lactic acid acts upon the casein in solutions containing salt1 causing it to dissolve to some extent1 thus forming the initial compounds of digestion4#ahd ,this solution of the casein is expressed physically by the stringing of the curds on a hot iron4 ,this causes the curds to mat1 producing a close1 solid body1 free from mechanical holes4 ,still further1 the development of this acid is necessary for the digestive activity of the pepsin in the rennet extract4 ,in some varieties of cheese1 as the ,swiss1 acid is not developed and the character of the cheese is much different from that of cheddar4 ,in all such varieties1 a great deal more trouble is experienced from the production of gassy curds1 because the development of the gas-producing bacteria is held in check by the rapid growth of the lactic acid-producing species4 ,bacteria in green cheese4 ,the conditions under which cheese is made permit of the development of bacteria throughout the entire process4 ,the cooking or heating of curds to expel the excessive moisture is never so high as to be fatal to germ life2 on the contrary1 the acidity of the curd and whey is continually increased by the development of bacteria in the same4 ,the body of green cheese fresh from the press is1 to a considerable extent1 dependent upon the acid produced in the curds4 ,if the curds are put to press in a relatively sweet condition the texture is open and porous4 ,the curd particles do not mat closely together and mechanical holes1 rough and irregular in outline1 occur4 ,very often1 at relatively high temperatures1 such cheese begin to huff1 soon after being taken from the press1 a condition due to the development of gas1 produced by gas-generating bacteria acting on the sugar in the curd4 ,this gas finds its way readily into these ragged holes1 greatly distending them1 as in ,fig4 #cj4 ,illustration3 ,,fig4 #cj4 ,l1 a sweet curd cheese direct from the press4 ,mechanical holes due to lack of acid development2 ,p1 same cheese four days later1 mechanical holes distended by development of gas4 ,physical changes in ripening cheese4 ,when a green cheese is taken from the press1 the curd is tough1 firm1 but elastic4 ,it has no value as a food product for immediate use1 because it lacks a desirable flavor and is not readily digestible4 ,it is nothing but precipitated casein and fat4 ,in a short time1 a deep-seated change occurs4 ,physically this change is demonstrated in the modification that the curd undergoes4 ,gradually it breaks down and becomes plastic1 the elastic1 tough curd being changed into a softened mass4 ,this change in texture of the cheese is also accompanied by a marked change in flavor4 ,the green cheese has no distinctively cheese flavor1 but in course of time1 with the gradual change of texture1 the peculiar flavor incident to ripe cheese is developed4 ,the characteristic texture and flavor are susceptible of considerable modification that is induced not only by variation in methods of manufacture1 but by the conditions under which the cheese are cured4 ,the amount of moisture incorporated with the curd materially affects the physical appearance of the cheese1 and the rate of change in the same4 ,the ripening temperature1 likewise the moisture content of the surrounding air1 also exerts a marked influence on the physical properties of the cheese4 ,to some extent the action of these forces is purely physical1 as in the gradual loss by drying1 but in other respects they are associated with chemical transformations4 ,chemical changes in ripening cheese4 ,coincident with the physical breaking down of the curd comes a change in the chemical nature of the casein4 ,the hitherto insoluble casein is gradually transformed into soluble nitrogenous substances 7caseone of ,duclaux1 or caseogluten of ,weigmann74 ,this chemical phenomenon is a breaking-down process that is analogous to the peptonization of proteids1 although in addition to the peptones and albumoses characteristic of peptic digestion1 amido-acids and ammonia are to be found4 ,the quantity of these lower products increases with the age of the cheese4 ,the chemical reaction of cheese is normally acid to phenolphthalein1 although there is generally no free acid1 as shown by ,congo red1 the lactic acid being converted into salts as fast as formed4 ,in very old cheese1 undergoing putrefactive changes1 especially on the outside1 an alkaline reaction may be present1 due to the formation of free ammonia4 ,the changes that occur in a ripening cheese are for the most part confined to the proteids4 ,according to most investigators the fat remains practically unchanged1 although the researches of ,weigmann and ,backe#ahe show that fatty acids are formed from the fat4 ,in the green cheese considerable milk-sugar is present1 but1 as a result of the fermentation that occurs1 this is rapidly converted into acid products4 ,bacterial flora of cheese4 ,it might naturally be expected that the green cheese1 fresh from the press1 would contain practically the same kind of bacteria that are in the milk1 but a study of cheese shows a peculiar change in the character of the flora4 ,in the first place1 fresh cottage cheese1 made by the coagulation of the casein through the action of acid1 has a more diversified flora than cheese made with rennet1 for the reason1 as given by ,lafar1#ahf that the fermentative process is farther advanced4 ,when different varieties of cheese are made from milk in the same locality1 the germ content of even the ripened product has a marked similarity1 as is illustrated by ,adametz's work#ahg on ,emmenthaler or ,swiss hard cheese1 and ,schweitzer ,hauskaese1 a soft variety4 ,of the nine species of bacilli and cocci found in mature ,emmenthaler1 eight of them were also present in ripened ,hauskaese4 ,different investigators have studied the bacterial flora of various kinds of cheese1 but as yet little comparative systematic work has been done4 ,freudenreich#ahh has determined the character and number of bacteria in ,emmenthaler cheese1 and ,russell#ahi the same for cheddar cheese4 ,the same general law has also been noted in ,canadian#aij and ,english#aia cheese4 ,at first a marked decrease in numbers is usually noted1 lasting for a day or two4 ,this is followed by an enormous increase1 caused by the rapid growth of the lactic-acid type4 ,the development may reach scores of millions and often over a hundred million organisms per gram4 ,synchronous with this increase1 the peptonizing and gas-producing bacteria gradually disappear4 ,this rapid development1 which lasts only for a few weeks1 is followed by a general decline4 ,in the ripening of cheese a question arises as to whether the process goes on throughout the entire mass of cheese1 or whether it is more active at or near the surface4 ,in the case of many of the soft cheese1 such as ,brie and limburger1 bacterial and mold development is exceedingly active on the exterior1 and the enzyms secreted by these organisms diffuse toward the interior4 ,that such a condition occurs in the hard type of cheese made with rennet is extremely improbable4 ,most observers agree that in this type of cheese the ripening progresses throughout the entire mass1 although ,adametz opposes this view and considers that in ,emmenthaler cheese the development of the specific aroma-producing organism occurs in the superficial layers4 ,jensen has shown1 however1 that the greatest amount of soluble nitrogenous products are to be found in the innermost part of the cheese1 a condition that is not reconcilable with the view that the most active ripening is on the exterior4#aib ,the course of development of bacteria in cheddar cheese is materially influenced by the ripening temperature4 ,in cheese ripened at relatively low temperatures 7#ej deg4-#ee deg4 ,f471#aic a high germ content is maintained for a much longer period of time than at higher temperatures4 ,under these conditions the lactic-acid type continues in the ascendancy as usual4 ,in cheese cured at high temperatures 7#hj deg4-#hf deg4 ,f47 the number of organisms is greatly diminished1 and they fail to persist in appreciable numbers for as long a time as in cheese cured at temperatures more frequently employed4 ,influence of temperature on curing4 ,temperature exerts a most potent influence on the quality of the cheese1 as determined not only by the rate of ripening but the nature of the process itself4 ,much of the poor quality of cheese is attributable to the effect of improper curing conditions4 ,probably in the initial stage of this industry cheese were allowed to ripen without any sort of control1 with the inevitable result that during the summer months the temperature generally fluctuated so much as to impair seriously the quality4 ,the effect of high temperatures 7#gj deg4 ,f4 and above7 is to produce a rapid curing1 and1 therefore1 a short lived cheese2 also a sharp1 strong flavor1 and generally a more or less open texture4 ,unless the cheese is made from the best quality of milk1 it is very apt to undergo abnormal fermentations1 more especially those of a gassy character4 ,illustration3 ,,fig4 #ca4 ,influence of curing temperature on texture of cheese4 ,upper row ripened eight months at #fj deg4 ,f42 lower row at #dj deg4 ,f4 ,where cheese is ripened at low temperatures1 ranging from #ej deg4 ,f4 down to nearly the freezing temperatures1 it is found that the quality is greatly improved4#aid ,such cheese are thoroughly broken down from a physical point of view even though they may not show such a high per cent of soluble nitrogenous products4 ,they have an excellent texture1 generally solid and firm1 free from all tendency to openness2 and1 moreover1 their flavor is clean and entirely devoid of the sharp1 undesirable tang that so frequently appears in old cheese4 ,the keeping quality of such cheese is much superior to the ordinary product4 ,the introduction of this new system of cheese-curing promises much from a practical point of view1 and undoubtedly a more complete study of the subject from a scientific point of view will aid materially in unraveling some of the problems as to flavor production4 ,theories of cheese curing4 ,within the last few years considerable study has been given the subject of cheese curing or ripening1 in order to explain how this physical and chemical transformation is brought about4 ,much of the misconception that has arisen relative to the cause of cheese ripening comes from a confusion of terms4 ,in the ordinary use of the word1 ripening or curing of cheese is intended to signify the sum total of all the changes that result in converting the green product as it comes from the press into the edible substance that is known as cured cheese4 ,as previously shown1 the most marked chemical transformation that occurs is that which has to do with the peptonization or breaking down of the casein4 ,it is true that under ordinary conditions this decomposition process is also accompanied with the formation of certain flavor-producing substances1 more or less aromatic in character2 but it by no means follows that these two processes are necessarily due to the same cause4 ,the majority of investigators have failed to consider these two questions of casein decomposition and flavor as independent1 or at least as not necessarily related4 ,they are undoubtedly closely bound together1 but it will be shown later that the problems are quite different and possibly susceptible of more thorough understanding when considered separately4 ,in the earlier theories of cheese ripening it was thought to be purely a chemical change1 but1 with the growth of bacteriological science1 evidence was forthcoming that seemed to indicate that the activity of organisms entered into the problem4 ,schaffer#aie showed that if milk was boiled and made into cheese1 the casein failed to break down4 ,adametz#aif added to green cheese various disinfectants1 as creolin and thymol1 and found that this practically stopped the curing process4 ,from these experiments he drew the conclusion that bacteria must be the cause of the change1 because these organisms were killed2 but when it is considered that such treatment would also destroy the activity of enzyms as well as vital ferments1 it is evident that these experiments were quite indecisive4 ,a determination of the nature of the by-products found in maturing cheese indicates that the general character of the ripening change is a peptonization or digestion of the casein4 ,until recently the most widely accepted views relating to the cause of this change have been those which ascribed the transformation to the activity of micro-organisms1 although concerning the nature of these organisms there has been no unanimity of opinion4 ,the overwhelming development of bacteria in all cheeses naturally gave support to this view2 and such experiments as detailed above strengthened the idea that the casein transformation could not occur where these ferment organisms were destroyed4 ,the very nature of the changes produced in the casein signified that to take part in this process any organism must possess the property of dissolving the proteid molecule1 casein1 and forming therefrom by-products that are most generally found in other digestive or peptonizing changes of this class4 ,digestive bacterial theory4 ,the first theory propounded was that of ,duclaux1#aig who in #ahhg advanced the idea that this change was due to that type of bacteria which is able to liquefy gelatin1 peptonize milk1 and cause a hydrolytic change in proteids4 ,to this widely-spread group that he found in cheese1 he gave the generic name ,tyrothrix 7cheese hairs74 ,according to him1 these organisms do not function directly as ripening agents1 but they secrete an enzym or unorganized ferment to which he applies the name casease4 ,this ferment acts upon the casein of milk1 converting it into a soluble product known as caseone4 ,these organisms are found in normal milk1 and if they function as casein transformers1 one would naturally expect them to be present1 at least frequently1 if not predominating in the ripening cheese2 but such is not the case4 ,in typical cheddar or ,swiss cheese1 they rapidly disappear 7p4 #afh71 although in the moister1 softer varieties1 they persist for considerable periods of time4 ,according to ,freudenreich1 even where these organisms are added in large numbers to the curd1 they soon perish1 an observation that is not regarded as correct by the later adherents to the digestive bacterial theory1 as ,adametz and ,winkler4 ,duclaux's experiments were made with liquid media for isolation purposes1 and his work1 therefore1 cannot be regarded as satisfactory as that carried out with more modern technical methods4 ,recently this theory has been revived by ,adametz1#aih who claims to have found in ,emmenthaler cheese a digesting species1 one of the ,tyrothrix type1 which is capable of peptonizing the casein and at the same time producing the characteristic flavor of this class of cheese4 ,this organism1 called by him ,bacillus nobilis1 the ,edelpilz of ,emmenthaler cheese1 has been subjected to comparative experiments1 and in the cheese made with pure cultures of this germ better results are claimed to have been secured4 ,sufficient experiments have not as yet been reported by other investigators to warrant the acceptance of the claims made relative to the effect of this organism4 ,lactic-acid bacterial theory4 ,it has already been shown that the lactic-acid bacteria seems to find in the green cheese the optimum conditions of development2 that they increase enormously in numbers for a short period1 and then finally decline4 ,this marked development1 coincident with the breaking down of the casein1 has led to the view which has been so ably expounded by ,freudenreich#aii that this type of bacterial action is concerned in the ripening of cheese4 ,this group of bacteria is1 under ordinary conditions1 unable to liquefy gelatin1 or digest milk1 or1 in fact1 to exert1 under ordinary conditions1 any proteolytic or peptonizing properties4 ,this has been the stumbling-block to the acceptance of this hypothesis1 as an explanation of the breaking down of the casein4 ,freudenreich has recently carried on experiments which he believes solve the problem4 ,by growing cultures of these organisms in milk1 to which sterile1 freshly precipitated chalk had been added1 he was able to prolong the development of bacteria for a considerable period of time1 and as a result finds that an appreciable part of the casein is digested2 but this action is so slow compared with what normally occurs in a cheese1 that exception may well be taken to this type of experiment alone4 ,weigmann#bjj inclines to the view that the lactic-acid bacteria are not the true cause of the peptonizing process1 but that their development prepares the soil1 as it were1 for those forms that are more directly concerned in the peptonizing process4 ,this they do by developing an acid substratum that renders possible the more luxuriant growth of the aroma-producing species4 ,according to ,gorini1#bja certain of the ,tyrothrix forms function at high temperatures as lactic acid producing bacteria1 while at lower temperatures they act as peptonizers4 ,on this basis he seeks to reconcile the discrepancies that appear in the experiments of other investigators4 ,digestive milk enzym theory4 ,in #ahig ,babcock and the writer#bjb showed that milk underwent digestive changes spontaneously when bacterial activity was suspended by the addition of such anaesthetics as ether1 chloroform and benzol4 ,the chemical nature of the by-products produced by this auto-digestion of milk resembles quite closely those found in ripened cheese1 except that ammonia is not produced as is the case in old cheese4 ,the cause of the decomposition of the casein1 they found to be due to the action of a milk enzym which is inherent to the milk itself4 ,this digestive ferment may be separated from fresh milk by concentrating centrifuge slime extracts by the usual physiological reagents4 ,this ferment1 called by them galactase1 on account of its origin in milk1 is a proteolytic enzym of the tryptic type4 ,its activity is destroyed by strong chemicals such as formaldehyde1 corrosive sublimate1 also when heated to #age deg4 ,f4 or above4 ,when such extracts are added to boiled milk1 the digestive process is started anew1 and the by-products produced are very similar to those noted in a normal cheese4 ,jensen#bjc has also shown that the addition of pancreatic extracts to cheese accelerated the formation of soluble nitrogenous products4 ,the action of galactase in milk and cheese has been confirmed by ,freudenreich#bjd and ,jensen1#bje as well as by ,american investigators1 and this enzym is now generally accepted as one of the factors concerned in the decomposition of the casein4 ,freudenreich believes it is able to change casein into albumose and peptones1 but that the lactic-acid bacteria are chiefly responsible for the further decomposition of the nitrogen to amid form4 ,failure before to recognize the presence of galactase in milk is attributable to the fact that all attempts to secure sterile milk had been made by heating the same1 in which case galactase was necessarily destroyed4 ,a brief exposure at #agf deg4 ,f4 is sufficient to destroy its activity1 and even an exposure at lower temperatures weakens its action considerably1 especially if the reaction of the medium is acid4 ,this undoubtedly explains the contradictory results obtained in the ripening of cheese from pasteurized milk1 such cheese occasionally breaking down in an abnormal manner4 ,the results mentioned on page #agb1 in which cheese failed to ripen when treated with disinfectants1--experiments which were supposed at that time to be the foundation of the bacterial theory of casein digestion--are now explicable on an entirely different basis4 ,in these cases the casein was not peptonized1 because these strong disinfectants destroyed the activity of the enzyms as well as the bacteria4 ,another important factor in the breaking down of the casein is the pepsin in the rennet extract4 ,the digestive influence of this agent was first demonstrated for cheddar cheese by ,babcock1 ,russell and ,vivian1#bjf and simultaneously1 although independently1 by ,jensen#bjg in ,emmenthaler cheese4 ,in this digestive action1 only albumoses and higher peptones are produced4 ,the activity of pepsin does not become manifest until there is about #j4c per cent4 acid which is approximately the amount developed in the cheddar process4 ,these two factors undoubtedly account for by far the larger proportion of the changes in the casein2 and yet1 the formation of ammonia in well ripened cheese is not accounted for by these factors4 ,this by-product is the main end product of proteid digestion by the liquefying bacteria but their apparent infrequency in cheese makes it difficult to understand how they can function prominently in the change1 unless the small quantity of digestive enzyms excreted by them in their growth in milk is capable of continuing its action until a cumulative effect is obtained4 ,although much light has been thrown on this question by the researches of the last few years1 the matter is far from being satisfactorily settled at the present time and the subject needs much more critical work4 ,if liquefying bacteria abound in the milk1 doubtless they exert some action1 but the role of bacteria is doubtless much greater in the production of flavor than in the decomposition of the curd4 ,conditions determining quality4 ,in determining the quality of cheese1 several factors are to be taken into consideration4 ,first and foremost is the flavor1 which determines more than anything else the value of the product4 ,this should be mild and pleasant1 although with age the intensity of the same generally increases but at no time should it have any bitter1 sour1 or otherwise undesirable taste or aroma4 ,texture registers more accurately the physical nature of the ripening4 ,the cheese should not be curdy and harsh1 but should yield quite readily to pressure under the thumb1 becoming on manipulation waxy and plastic instead of crumbly or mealy4 ,body refers to the openness or closeness of the curd particles1 a close1 compact mass being most desirable4 ,the color of cheese should be even1 not wavy1 streaked or bleached4 ,for a cheese to possess all of these characteristics in an optimum degree is to be perfect in every respect--a condition that is rarely reached4 ,so many factors influence this condition that the problem of making a perfect cheese becomes exceedingly difficult4 ,not only must the quality of the milk--the raw material to be used in the manufacture--be perfectly satisfactory1 but the factory management while the curds are in the vat demands great skill and careful attention2 and finally1 the long period of curing in which variation in temperature or moisture conditions may seriously affect the quality1--all of these stages1 more or less critical1 must be successfully gone through1 before the product reaches its highest state of development4 ,it is of course true that many phases of this complex series of processes have no direct relation to bacteria1 yet it frequently happens that the result attained is influenced at some preceding stage by the action of bacteria in one way or another4 ,thus the influence of the acidity developed in the curds is felt throughout the whole life of the cheese1 an over-development of lactic-acid bacteria producing a sour condition that leaves its impress not only on flavor but texture4 ,an insufficient development of acid fails to soften the curd-particles so as to permit of close matting1 the consequence being that the body of the cheese remains loose and open1 a condition favorable to the development of gas-generating organisms4 ,production of flavor4 ,the importance of flavor as determining the quality of cheese makes it imperative that the nature of the substances that confer on cheese its peculiar aromatic qualities and taste be thoroughly understood4 ,it is to be regretted that the results obtained so far are not more satisfactory1 for improvement in technique is hardly to be expected until the reason for the process is thoroughly understood4 ,the view that is most generally accepted is that this most important phase of cheese curing is dependent upon bacterial activity1 but the organisms that are concerned in this process have not as yet been satisfactorily determined4 ,in a number of cases1 different species of bacteria have been separated from milk and cheese that have the power of producing aromatic compounds that resemble1 in some cases1 the peculiar flavors and odors that characterize some of the foreign kinds of cheese2 but an introduction of these into curd has not resulted in the production of the peculiar variety1 even though the methods of manufacture and curing were closely followed4 ,the similarity in germ content in different varieties of cheese made in the same locality has perhaps a bearing on this question of flavor as related to bacteria4 ,of the nine different species of bacteria found in ,emmenthaler cheese by ,adametz1 eight of them were also present in ripened ,hauskaese4 ,if specific flavors are solely the result of specific bacterial action1 it might naturally be expected that the character of the flora would differ4 ,some suggestive experiments were made by ,babcock and ,russell on the question of flavor as related to bacterial growth1 by changing the nature of the environment in cheese by washing the curds on the racks with warm water4 ,in this way the sugar and most of the ash were removed4 ,under such conditions the character of the bacterial flora was materially modified4 ,while the liquefying type of bacteria was very sparse in normal cheddar1 they developed luxuriantly in the washed cheese4 ,the flavor at the same time was markedly affected4 ,the control cheddar was of good quality1 while that made from the washed curds was decidedly off1 and in the course of ripening became vile4 ,it may be these two results are simply coincidences1 but other data#bjh bear out the view that the flavor was to some extent related to the nature of the bacteria developing in the cheese4 ,this was strengthened materially by adding different sugars to washed curds1 in which case it was found that the flavor was much improved1 while the more normal lactic-acid type of bacteria again became predominant4 ,ripening of moldy cheese4 ,in a number of foreign cheeses1 the peculiar flavor obtained is in part due to the action of various fungi which grow in the cheese1 and there produce certain by-products that flavor the cheese4 ,among the most important of these are the ,roquefort cheese of ,france1 ,stilton of ,england1 and ,gorgonzola of ,italy4 ,roquefort cheese is made from goat's or cow's milk1 and in order to introduce the desired mold1 which is the ordinary bread-mold1 ,penicillium glaucum1 carefully-prepared moldy bread-crumbs are added to the curd4 ,at ordinary temperatures this organism develops too rapidly1 so that the cheese to ripen properly must be kept at a low temperature4 ,the town of ,roquefort is situated in a limestone country1 in a region full of caves1 and it is in these natural caves that most of the ripening is done4 ,these caverns are always very moist and have a temperature ranging from #ce deg4 to #dd deg4 ,f41 so that the growth of the fungus is retarded considerably4 ,the spread of the mold throughout the ripening mass is also assisted in a mechanical way4 ,the partially-matured cheese are run through a machine that pricks them full of small holes4 ,these slender canals allow the mold organism to penetrate the whole mass more thoroughly1 the moldy straw matting upon which the ripening cheese are placed helping to furnish an abundant seeding of the desired germ4 ,when new factories are constructed it is of advantage to introduce this necessary germ in quantities1 and the practice is sometimes followed of rubbing the walls and cellars of the new location with material taken from the old established factory4 ,in this custom1 developed in purely an empirical manner1 is to be seen a striking illustration of a bacteriological process crudely carried out4 ,in the ,stilton cheese1 one of the highly prized moldy cheeses of ,england1 the desired mold fungus is introduced into the green cheese by exchanging plugs taken with a cheese trier from a ripe ,stilton4 ,ripening of soft cheese4 ,the type of ripening which takes place in the soft cheeses is materially different from that which occurs in the hard type4 ,the peptonizing action does not go on uniformly throughout the cheese1 but is hastened by the development of molds and bacteria on the outside that exert a solvent action on the casein4 ,for this reason1 soft cheeses are usually made up in small sizes1 so that this action may be hastened4 ,the organisms that take part in this process are those that are able to form enzyms 7similar in their action to trypsin1 galactase1 etc471 and these soluble ferments gradually diffuse from the outside through the cheese4 ,most of these peptonizing bacteria are hindered in their growth by the presence of lactic acid1 so that in many cases the appearance of the digesting organisms on the surface is delayed until the acidity of the mass is reduced to the proper point by the development of other organisms1 principally molds1 which prefer an acid substratum for their growth4 ,in ,brie cheese a blue coating of mold develops on the surface4 ,in the course of a few weeks1 a white felting appears which later changes to red4 ,this slimy coat below the mold layer is made up of diverse species of bacteria and fungi that are able to grow after the acid is reduced by the blue mold4 ,the organisms in the red slimy coat act upon the casein1 producing an alkaline reaction that is unfavorable to the growth of the blue mold4 ,two sets of organisms are1 therefore essential in the ripening process1 one preparing the soil for the ferment that later produces the requisite ripening changes4 ,as ordinarily carried on1 the process is an empirical one1 and if the red coat does not develop as expected1 the maker resorts to all kinds of devices to bring out the desired ferment4 ,the appearance of the right form is dependent1 however1 upon the proper reaction of the cheese1 and if this is not suitable1 the wished-for growth will not appear4 ,,influence ,,of ,,bacteria ,,in ,,abnormal ,,cheese ,,processes4 ,the reason why cheese is more subject to abnormal fermentation than butter is because its high nitrogen content favors the continued development of bacteria for some time after it is made4 ,it must be borne in mind1 in considering the more important of these changes1 that not all defective conditions in cheese are attributable to the influence of living organisms4 ,troubles frequently arise from errors in manufacturing details1 as too prolonged cooking of curds1 too high heating1 or the development of insufficient or too much acid4 ,then again1 the production of undesirable flavors or impairment in texture may arise from imperfect curing conditions4 ,our knowledge regarding the exact nature of these indefinite faults is as yet too inadequate to enable many of these undesirable conditions to be traced to their proper source2 but in many cases the taints observed in a factory are due to the abnormal development of certain bacteria1 capable of evolving unpleasant or even putrid odors4 ,most of them are seeded in the milk before it comes to the factory and are due to careless manipulation of the milk while it is still on the farm4 ,others gain access to the milk in the factory1 owing to unclean conditions of one sort or another4 ,sometimes the cheese-maker is able to overcome these taints by vigorous treatment1 but often they pass on into the cheese1 only to detract from the market value of the product4 ,most frequently these off flavors appear in cheese that are cured at too high temperatures1 say above #fe deg4 ,f4 ,gassy fermentations in cheese4 ,one of the worst and at the same time most common troubles in cheese-making is where the cheese undergoes a fermentation marked by the evolution of gas4 ,the presence of gas is recognized by the appearance either of spherical or lens-shaped holes of various sizes in the green cheese2 often they appear in the curd before it is put to press4 ,usually in this condition the curds look as if they had been punctured with a pin1 and are known as pin holey curds4 ,where the gas holes are larger1 they are known as ,swiss holes from their resemblance to the normal holes in the ,swiss product4 ,if the development of gas is abundant1 these holes are restricted in size4 ,often the formation of gas may be so intense as to cause the curds to float on the surface of the whey before they are removed4 ,such curds are known as floaters or bloaters4 ,if gassy curds are put to press1 the abnormal fermentation may continue4 ,the further production of gas causes the green cheese to huff or swell1 until it may be considerably distorted as in ,fig4 #cc4 ,in such cases the texture of the cheese is greatly injured1 and the flavor is generally impaired4 ,illustration3 ,,fig4 #cc4 ,cheese made from gassy milk4 ,such abnormal changes may occur at any season of the year1 but the trouble is most common in summer1 especially in the latter part4 ,this defect is less likely to occur in cheese that is well cheddared than in sweet curd cheese4 ,when acidity is produced1 these gassy fermentations are checked1 and in good cheddar the body is so close and firm as not readily to permit of gaseous changes4 ,in ,swiss cheese1 which is essentially a sweet curd cheese1 these fermentations are very troublesome4 ,where large holes are formed in abundance 7blaehen71 the trouble reaches its maximum4 ,if the gas holes are very numerous and therefore small it is called a nissler4 ,sometimes the normal eyes are even wanting when it is said to be blind or a glaesler4 ,illustration3 ,,fig4 #cd4 ,block ,swiss cheese showing gassy fermentation4 ,one method of procedure which is likely to cause trouble in ,swiss factories is often produced by the use of sour1 fermented whey in which to soak the natural rennets4 ,freudenreich and ,steinegger#bji have shown that a much more uniform quality of cheese can be made with rennet extract if it is prepared with a starter made from a pure lactic ferment4 ,the cause of the difficulty has long been charged to various sources1 such as a lack of aeration1 improper feeding1 retention of animal gases1 etc41 but in all these cases it was nothing more than a surmise4 ,very often the milk does not betray any visible symptom of fermentation when received1 and the trouble is not to be recognized until the process of cheese-making is well advanced4 ,studies from a biological standpoint have1 however1 thrown much light on this troublesome problem2 and it is now known that the formation of gas1 either in the curd or after it has been put to press1 is due entirely to the breaking down of certain elements1 such as the sugar of milk1 due to the influence of various living germs4 ,this trouble is1 then1 a type fermentation1 and is1 therefore1 much more widely distributed than it would be if it was caused by a single specific organism4 ,these gas-producing organisms are to be found1 sparingly at least1 in almost all milks1 but are normally held in check by the ordinary lactic species4 ,among them are a large number of the bacteria1 although yeasts and allied germs are often present and are likewise able to set up fermentative changes of this sort4 ,in these cases the milk-sugar is decomposed in such a way as to give off ,,co#b and ,h1 and in some cases1 alcohol4 ,russell and ,hastings#baj found a lactose-splitting yeast in a severe outbreak of gassy cheese in a ,swiss factory4 ,in this case the gas did not develop until the cheese were a few weeks old4 ,in severe cases the cheese actually cracked to pieces4 ,according to ,guillebeau1 a close relation exists between those germs that are able to produce an infectious inflammation 7mastitis7 in the udder of the cow and some forms capable of gas evolution4 ,if pure cultures of these gas-producing bacteria are added to perfectly sweet milk1 it is possible to artificially produce the conditions in cheese that so frequently appear in practice4 ,treatment of pin-holey curds4 ,when this type of fermentation appears during the manufacture of the cheese1 the maker can control it in part within certain limits4 ,these methods of treatment are1 as a rule1 purely mechanical1 as when the curds are piled and turned1 and subsequently ground in a curd mill4 ,after the gas has been forced out1 the curds are then put to press and the whole mats into a compact mass4 ,another method of treatment based upon bacteriological principles is the addition of a starter to induce the formation of acid4 ,where acid is developed as a result of the growth of the lactic-acid bacteria1 the gas-producing species do not readily thrive4 ,another reason why acid aids in repressing the development of gas is that the curd particles are partially softened or digested by the action of the acid4 ,this causes them to mat together more closely1 and there is not left in the cheese the irregular mechanical openings in which the developing gas may find lodgment4 ,another method that is also useful with these curds is to employ salt4 ,this represses gaseous fermentations1 and the use of more salt than usual in making the cheese will very often restrain the production of gas4 ,tendency to form gas in ,edam cheese is controlled by the addition of a starter prepared from slimy whey 7lange wei7 which is caused by the development of an acid-forming organism4 ,some have recommended the custom of washing the curds to remove the whey and the gas-producing bacteria contained therein4 ,care must be taken not to carry this too far1 for the removal of the sugar permits taint-producing organisms to thrive4#baa ,the temperature at which the cheese is cured also materially affects the development of gas4 ,at high curing temperatures1 gas-producing organisms develop rapidly2 therefore more trouble is experienced in summer than at other seasons4 ,if milks which are prone to undergo gassy development are excluded from the general supply1 it would be possible to eliminate the source of the entire trouble4 ,to aid in the early recognition of such milks that are not apparently affected when brought to the factory1 fermentation or curd tests 7p4 #gf7 are of great value4 ,the use of this test in the hands of the factory operator often enables him to detect the exact source of the trouble1 which may frequently be confined to the milk delivered by a single patron4 ,fruity or sweet flavor4 ,not infrequently the product of a factory may acquire during the process of ripening what is known as a sweet or fruity flavor4 ,this flavor resembles the odor of fermented fruit or the bouquet of certain kinds of wine4 ,it has been noted in widely different sections of the country and its presence bears no relation to the other qualities of the cheese4 ,the cause of this trouble has recently been traced#bab to the presence of various kinds of yeasts4 ,ordinarily yeasts are rarely present in good cheese1 but in cheese affected with this trouble they abound4 ,the addition of starters made from yeast cultures resulted in the production of the undesirable condition4 ,mottled cheese4 ,the color of cheese is sometimes cut to that extent that the cheese presents a wavy or mottled appearance4 ,this condition is apt to appear if the ripening temperature is somewhat high1 or larger quantities of rennet used than usual4 ,the cause of the defect is obscure1 but it has been demonstrated that the same is communicable if a starter is made by grating some of this mottled cheese into milk4 ,the bacteriology of the trouble has not yet been worked out1 but the defect is undoubtedly due to an organism that is able to grow in the ripening cheese4 ,it has been claimed that the use of a pure lactic ferment as a starter enables one to overcome this defect4 ,bitter cheese4 ,bitter flavors are sometimes developed in cheese especially where the ripening process is carried on at a low temperature in the presence of an excess of moisture for a considerable length of time4 ,guillebeau#bac isolated several forms from ,emmenthaler cheese which he connected with udder inflammation that were able to produce a bitter substance in cheese4 ,von ,freudenreich#bad has described a new form ,micrococcus casei amari 7micrococcus of bitter cheese7 that was found in a sample of bitter cheese4 ,this germ is closely related to ,conn's micrococcus of bitter milk4 ,it develops lactic acid rapidly1 coagulating the milk and producing an intensely bitter taste in the course of one to three days4 ,when milk infected with this organism is made into cheese1 there is formed in a few days a decomposition product that imparts a marked bitter flavor to the cheese4 ,harrison#bae has recently found a yeast that grows in the milk and also in the cheese which produces an undesirable bitter change4 ,it is peculiar that some of the organisms that are able to produce bitter products in milk do not retain this property when the milk is worked up into cheese4 ,putrid or rotten cheese4 ,sometimes cheese undergoes a putrefactive decomposition in which the texture is profoundly modified and various foul smelling gases are evolved4 ,these often begin on the exterior as small circumscribed spots that slowly extend into the cheese1 changing the casein into a soft slimy mass4 ,then1 again1 the interior of the cheese undergoes this slimy decomposition4 ,the soft varieties are more prone toward this fermentation than the hard1 although the firm cheeses are by no means exempt from the trouble4 ,the ,verlaufen or running of limburger cheese is a fermentation allied to this4 ,it is where the inside of the cheese breaks down into a soft semi-fluid mass4 ,in severe cases1 the rind may even be ruptured1 in which case the whole interior of the cheese flows out as a thick slimy mass1 having sometimes a putrid odor4 ,the conditions favoring this putrid decomposition are usually associated with an excess of moisture1 and an abnormally low ripening temperature4 ,rusty spot4 ,this name is applied to the development of small yellowish-red or orange spots that are formed sometimes throughout the whole mass of cheddar cheese4 ,a close inspection shows the colored points to be located along the edges of the curd particles4 ,according to ,harding1#baf this trouble is most common in spring and fall4 ,the cause of the difficulty has been traced by ,connell#bag to the development of a chromogenic bacterium1 ,bacillus rudensis4 ,the organism can be most readily isolated on a potato surface rather than with the usual isolating media1 agar or gelatin4 ,other pigment changes4 ,occasionally1 with the hard type of cheese1 but more frequently with the softer foreign varieties1 various abnormal conditions arise that are marked by the production of different pigments in or on the cheese4 ,more frequently these are merely superficial and affect only the outer layers of the cheese4 ,generally they are attributable to the development of certain chromogenic organisms 7bacteria1 molds and yeasts71 although occasionally due to other causes1 as in the case of a blue discoloration sometimes noted in foreign cheese made in copper kettles4#bah ,de ,vries#bai has described a blue condition that is found in ,edam cheese4 ,it appears first as a small blue spot on the inside1 increasing rapidly in size until the whole mass is affected4 ,this defect he was able to show was produced by a pigment-forming organism1 ,b4 cyaneo-fuscus4 ,by the use of slimy whey 7lange wei7 this abnormal change was controlled4 ,moldy cheese4 ,with many varieties of cheese1 especially some of the foreign types1 the presence of mold on the exterior is not regarded as detrimental2 in fact a limited development is much desired4 ,in hard rennet cheese as cheddar or ,swiss1 the market demands a product free from mold1 although it should be said that this condition is imposed by the desire to secure a good-looking cheese rather than any injury in flavor that the mold causes4 ,mold spores are so widely distributed that1 if proper temperature and moisture conditions prevail1 these spores will always develop4 ,at temperatures in the neighborhood of #dj deg4 ,f4 and below1 mold growth is exceedingly slow1 and often fructification does not occur1 the only evidence of the mold being the white1 felt-like covering that is made up of the vegetating filaments4 ,the use of paraffin has been suggested as a means of overcoming this growth1 the cheese being dipped at an early stage into melted paraffin4 ,recent experiments have shown that off flavors sometimes develop where cheese are paraffined directly from the press4 ,if paraffin is too hard1 it has a tendency to crack and separate from the rind1 thus allowing molds to develop beneath the paraffin coat1 where the conditions are ideal as to moisture1 for evaporation is excluded and the air consequently saturated4 ,the use of formalin 7#b solution7 has been suggested as a wash for the outside of the cheese4 ,this substance or sulfur is also applied in a gaseous form4 ,double bandaging is also resorted to as a means of making the cheese more presentable through the removal of the outer bandage4 ,the nature of these molds has not been thoroughly studied as yet4 ,the ordinary blue-green bread mold1 ,penicillium glaucum1 is most frequently found1 but there are numerous other forms that appear1 especially at low temperatures4 ,poisonous cheese4 ,cases of acute poisoning arising from the ingestion of cheese are reported from time to time4 ,vaughan has succeeded in showing that this condition is due to the formation of a highly poisonous alkaloid which he has isolated1 and which he calls tyrotoxicon4#bbj ,this poisonous ptomaine has also been demonstrated in milk and other milk products1 and is undoubtedly due to the development of various putrefactive bacteria that find their way into the milk4 ,it seems quite probable that the development of these toxic organisms can also go on in the cheese after it is taken from the press4 ,prevention or cheese defects4 ,the defective conditions previously referred to can rarely be overcome in cheese so as to improve the affected product1 for they only become manifest in most cases during the later stages of the curing process4 ,the only remedy against future loss is to recognize the conditions that are apt to prevail during the occurrence of an outbreak and see that the cheese are handled in such a way as to prevent a recurrence of the difficulty4 ,many abnormal and undesirable results are incident to the manufacture of the product1 such as sour or mealy cheese1 conditions due to the development of too much acid in the milk or too high a cook4 ,these are under the direct control of the maker and for them he alone is responsible4 ,the development of taints due to the growth of unwelcome bacteria that have gained access to the milk while it is yet on the farm are generally beyond the control of the cheese maker1 unless they are so pronounced as to appear during the handling of the curds4 ,if this does occur he is sometimes able1 through the intervention of a starter or by varying some detail in making1 to handle the milk in such a way as to minimize the trouble1 but rarely is he able to eliminate it entirely4 ,one of the most strenuous duties which the maker must perform at all times is to point out to his patrons the absolute necessity of their handling the milk in such a way as to prevent the introduction of organisms of a baleful type4 ,,footnotes3 #agh ,russell1 #ac ,rept4 ,wis4 ,expt4 ,stat41 #ahif1 p4 #aab2 ,campbell1 ,trans4 ,high4 ,agr4 ,soc4 ,scotland1 #e ser41 #ahih1 #aj3aha4 #agi ,winkler1 ,milch ,zeit4 7,hildesheim71 ,nov4 #bd1 #aijj4 #ahj ,campbell1 ,no4 ,brit41 ,agric41 ,may #ab1 #ahig4 #aha ,weigmann1 ,milch ,zeit41 ,no4 #ej1 #ahhi4 #ahb ,klein1 ,milch ,zeit4 7,hildesheim71 ,no4 #ag1 #aijj4 #ahc ,adametz1 ,landw4 ,jahr41 #ah3bef4 #ahd ,van ,slyke and ,hart1 ,bull4 #bad1 ,n4 ,y4 ,expt4 ,stat41 ,july #aijb4 #ahe ,milch ,zeit41 #ahih1 ,no4 #di4 #ahf ,lafar1 ,technical ,mycology1 p4 #baf4 #ahg ,adametz1 ,landw4 ,jahr41 #ah3bbh4 #ahh ,freudenreich1 ,landw4 ,jahr4 d4 ,schweiz1 #d3ag2 #e3af4 #ahi ,russell1 #ac ,rept4 ,wis4 ,expt4 ,stat41 #ahif1 p4 #ie4 #aij ,harrison and ,connell1 ,rev4 gen4 du ,lait1 ,nos4 #d1 #e1 #f1 #g and #h1 #aijc-jd4 #aia ,lloyd1 ,bath and ,west of ,eng4 ,soc4 ,rept41 #ahib1 #b3ahj4 #aib ,freudenreich1 ,landw4 ,jahr4 d4 ,schweiz1 #aijj2 ,adametz1 ,oest4 ,molk4 ,zeit41 #ahii1 ,no4 #g4 #aic ,russell1 #ad ,wis4 ,expt4 ,stat41 #ahig1 p4 #bjc4 ,harrison and ,connell1 ,rev4 gen4 du ,lait ,nos4 #d1 etc41 #aijc-jd4 #aid ,babcock and ,russell1 #ah ,rept4 ,wis4 ,expt4 ,stat41 #aija4 ,dean1 ,harrison and ,harcourt1 ,bull4 #aba1 ,ont4 ,agr'l4 ,coll41 ,june #aijb4 #aie ,schaffer1 ,milch ,zeit41 #ahhi1 p4 #adf4 #aif ,adametz1 ,landw4 ,jahr41 #ah3bfa4 #aig ,duclaux1 ,le ,lait1 p4 #bac4 #aih ,adametz1 ,oest4 ,molk4 ,zeit41 #aijj1 ,nos4 #af-ah4 #aii ,freudenreich1 ,landw4 ,jahr4 d4 ,schweiz1 #ahig1 p4 #he4 #bjj ,weigmann1 ,cent4 f4 ,bakt41 ,,ii ,abt41 #ahih1 #d3eic2 also #ahii1 #e3fcj4 #bja ,gorini1 ,abs4 in ,expt4 ,stat4 ,rec41 #aa3chh4 #bjb ,babcock and ,russell1 #ad ,rept4 ,wis4 ,expt4 ,stat41 #ahig1 p4 #afa4 #bjc ,jensen1 ,cent4 f4 ,bakt41 ,,ii ,abt41 #c3geb4 #bjd ,freudenreich1 ,cent4 f4 ,bakt41 ,,ii ,abt41 #aijj1 #f3ccb4 #bje ,jensen1 ,ibid41 #aijj1 #f3gcd4 #bjf #ag ,rept4 ,wis4 ,expt4 ,stat41 #aijj1 p4 #ajb4 #bjg ,jensen1 ,landw4 ,jahr4 d4 ,schweiz1 #aijj4 #bjh ,babcock and ,russell1 #ah ,rept4 ,wis4 ,expt4 ,stat41 #aija4 #bji ,cent4 f4 ,bakt4 #ahii1 p4 #ad4 #baj ,bull4 #abh1 ,wis4 ,expt4 ,stat41 ,sept4 #aije4 #baa ,babcock and ,russell1 #ah ,rept4 ,wis4 ,expt4 ,stat41 #aija4 #bab ,harding1 ,rogers and ,smith1 ,bull4 #ahc1 ,n4 ,y4 7,geneva7 ,expt4 ,stat41 ,dec41 #aijj4 #bac ,guillebeau1 ,landw4 ,jahr41 #ahij1 p4 #bg4 #bad ,freudenreich1 ,fueehl4 ,landw4 ,ztg41 #dc3cfa4 #bae ,harrison1 ,bull4 #abc ,ont4 ,agr'l4 ,coll41 ,may1 #aijb4 #baf ,bull4 #ahc1 ,n4 ,y4 7,geneva7 ,expt4 ,stat41 ,dec4 #aijj4 #bag ,connell1 ,bull4 ,canadian ,dept4 of ,agr41 #ahig4 #bah ,schmoeger1 ,milch ,zeit41 #ahhc1 p4 #dhc4 #bai ,de ,vries1 ,milch ,zeit41 #ahhh1 pp4 #hfa1 #hhe4 #bbj ,zeit4 f4 physiol4 ,chemie1 #aj3adf4 ,,index4 ,acid1 effect of1 on churning1 #acg2 in butter-making1 #ach4 ,acid test1 #eb4 ,aeration of milk1 #ei4 ,aerobic bacteria1 #g4 ,alcoholic fermentation in milk1 #gb4 ,anaerobic bacteria1 #g4 ,animal1 influence of1 on milk infection1 #cd4 ,animal odor1 #ef4 ,anthrax1 #id4 ,antiseptics1 #i1 #hh4 ,aroma1 of butter1 #adj4 ,bacillus3 definition of1 #b4 acidi lactici1 #fd2 cyaneo-fuscus1 #ahh2 cyanogenus1 #gd2 foetidus lactis1 #aeg2 lactis aerogenes1 #fe2 lactis erythrogenes1 #gd2 lactis saponacei1 #fg2 lactis viscosus1 #ga2 nobilis1 #afb1 #agd2 prodigiosus1 #gd2 rudensis1 #ahh2 synxanthus1 #ge2 tuberculosis1 #hd4 ,bacteria3 on hairs1 #ce2 kinds in milk1 #fc2 in barn air1 #db2 in milk pails1 #bg2 in butter1 #aed2 classification of1 #d2 in cheese1 #afj2 culture of1 #ag2 in cream1 #abh2 discovery of1 #a2 external conditions affecting1 #h2 form of1 #b2 in butter1 #adb2 in butter-making1 #abg2 in centrifuge slime1 #ci2 ,in fore milk1 #bh2 in rennet1 #afc2 ,in separator slime1 #ci2 manure1 #cg2 number of1 in milk1 #ej4 ,distribution of3 milk of ,american cities1 #ej2 ,european cities1 #ej2 in relation to cheese1 #afh4 ,of disease3 anthrax1 #id2 cholera1 #ih2 diphtheria1 #ii2 lockjaw1 #id2 toxic1 #ajj2 tuberculosis1 #hd2 typhoid fever1 #ih4 ,methods of study of3 culture1 #ae2 culture media1 #ac2 isolation1 #ad4 ,bitter butter1 #aeh2 cheese1 #ahi2 milk1 #gb4 ,bloody milk1 #gd4 ,blue cheese1 #aia2 milk1 #gd4 ,bovine tuberculosis1 #hd4 ,brie cheese1 #ahb4 ,butter3 bacteria in1 #aed2 bitter1 #aeh2 cowy1 #aeg2 fishy1 #aei2 lardy1 #aeg2 moldy1 #aeh2 mottled1 #aef2 oily1 #aeh2 putrid1 #aef2 rancid1 #aee2 tallowy1 #aeg2 turnip flavor in1 #aeg4 ,making3 aroma1 #adj2 flavor in1 #adj2 pure culture1 #adc2 in ripening of cream1 #acf4 ,butyric acid fermentation1 #fi4 ,by-products of factory1 methods of preserving1 #be4 ,casease1 #fh4 ,caseone1 #fh4 ,centrifugal force1 cleaning milk by1 #ch4 ,cheese3 bacterial flora of1 #afh2 bitter1 #ahi2 blue1 #ahg2 ,brie1 #ahb2 ,edam1 #gb1 #afb2 ,emmenthaler1 #ahe2 flavor of1 #agi2 gassy fermentations in1 #ahc2 ,gorgonzola1 #ahj2 molds on1 #aia2 mottled1 #ahi2 nissler1 #ahe2 poisonous1 #aib2 putrid1 #aij2 ripening of moldy1 #ahj2 ripening of soft1 #aha2 ,roquefort1 #ahj2 rusty spot in1 #ahh2 ,stilton1 #ahj2 ,swiss1 #ahe4 ,making and curing3 chemical changes in curing1 #aff2 influence of temperature on curing1 #afi2 influence of rennet1 #agg2 physical changes in curing1 #afe2 prevention of defects1 #aic2 starters in1 #afa2 temperature in relation to bacterial influence1 #afi4 ,theories of curing3 digestive1 #agc2 galactase1 #age1 #agg2 lactic acid1 #agd4 ,chemical changes in cheese-ripening1 #aff4 ,chemical disinfectants in milk3 bleaching powder1 #ha2 corrosive sublimate1 #ha2 formalin1 #hj2 sulfur1 #hj2 whitewash1 #ha2 vitriol1 #ha4 ,chemical preservatives1 #hj4 ,children1 milk for1 #de4 ,cholera in milk1 #ih4 ,classification by separator1 #ch4 ,coccus1 definition of1 #b4 ,cold1 influence on bacteria1 #h1 #dh4 ,contamination of milk through disease germs1 #ie1 #aia4 ,covered milk pails1 #da4 ,cream1 bacterial changes in1 #ace2 mechanical causes for bacteria in1 #ace2 pasteurized1 #aac2 restoration of consistency of pasteurized1 #acb4 ,ripening of1 #acf2 advantage of 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