The Story of Germ Life

ng. During these many centuries certain methods of procedure have been developed which produce desired results. These methods, however, have been devised simply from

ave been teaching us that the new methods are to be found along the line of the application of the discoveries of modern bacteriology. We have been learning that the dairyman is more closely related to bacteria and their activities than almost any other class o

F BACTERI

y, it has been demonstrated that practically all of the normal changes which occur in milk after its secretion are caused by the growth of bacteria. This, too, was long denied, and for quite a number of years after putrefactions and fermentations were generally acknowledged to be caused by the growth of micro- organisms, the changes which occurred in milk were excepted from the rule. The uniformity with which milk will sour, and the difficulty, or seeming imp

s sure to be contaminated by bacteria, and by the time it has entered the milk pail it contains frequently as many as half a million, or even a million, bacteria in every cubic inch of the milk. This seems almo

place for millions of bacteria. The hind quarters of a cow are commonly in a condition of much filth, for the farmer rarely grooms his cow, and during the milking, by her movements, by the switching of her tail, and by the rubbing she gets from the milker, no inconsiderable amount of this dirt and filth is brushed off and falls into the milk pail The farmer understands this source of dirt and usually feels it necessary to strain the milk after the milking. But the straining it receives through a coarse cloth, while it will remove the coarser particles of dirt, has no effect upon the bacteria, for these pass through any strainer unimpeded. Again, the milk vessels themselves contain bacteria, for they are never washed absolutely clean. After the most thorough washing which the milk pail receives from the kitchen, there will always be

arket milk may contain as many as five hundred millions per cubic inch; and while this is a decidedly extreme number, milk that is a day old will almost always contain many millions in each cubic inch, the number depending upon the age of the milk and its temperature. During this growth the bacteria have, of course, not been without their effect. Recognising as we do that bacteria are agents for ch

OF BACTER

ormal property of milk. To-day, however, the phenomenon is well understood. It is due to the action of certain of the milk bacteria upon the milk sugar which converts it into lactic acid, and this acid gives the sour taste and curdles the milk. A

us acidi lactici always present, they found that quite a number of different species of bacteria have the power of souring milk, and are found in different specimens of soured milk. The number of species of bacteria which have been found to sour milk has increased until something over a hundred are known to have this power. These different species do not affect the milk in the same way. All produce some acid, but they differ in the kind and the amount of acid, and especially in the other changes which are effected at the same time that the milk is soured, so that the resulting soured milk is quite variable. In spite

or acquires an unpleasant "tainted" taste, or, again, a "soapy" taste. Occasionally a dairyman finds his milk becoming slimy, instead of souring and curdling in the normal fashion. At such times, after a number of hours, the milk becomes so slimy that it can be drawn into long threads. Such an infection proves very troublesome, for many a time

number produce a "tainted" and one a "soapy" taste. A score or more have been found which have the power of rendering the milk slimy. Two different species at least have the power of turning the milk to sky-blue colour; two or three produce red pigmen

ost of these troublesome bacteria come from some unusual sources of infection. By unusual sources are meant those which the exercise of care will avoid. It is true that the souring bacteria appear to be so universally distributed that they can not be avoided by any ordinary means. But all other troublesome bacteria appear to be within control. The milkman must remember that the sources of the troubles which are liable to arise in his milk are in some form of filth: either filth on the cow, or dust in the hay which is scattered through the barn, or dirt on cows' udders, or some other unusual and avoidable source. These sources, from what we have already noticed, will always furnish the milk with bacteria; but under common conditions, and when the cow is kept in conditions of ordinary cleanliness, and frequently even when not cleanly, will only furnish bacteria that produce the universal souring. R

an. To avoid their evil influence have been designed all the methods of caring for the dairy and the barn, all the methods of distributing milk in ice cars. Moreover, all the special devices connected with

IN BUTT

jority of butter-consuming countries a different quality of butter is desired, and the cream is subjected to a process known as "ripening" or "souring" before it is churned. In ripening, the cream is simply allowed to stand in a vat for a period varying from twelve hours to two or three days, according to circumstances. During this period certain changes take place therein. The bacteria which were in the cream originally, get an opportunity to grow, and by the time the ripening is complete they become extremely numerous. As a result, the character of the cream changes just as the milk is changed under similar circumstances. It becomes somewhat soured; it becomes slightly curdled, and acquir

eld of butter therefrom. The great object of the ripening, however, is to develop in the butter the peculiar flavour and aroma which is characteristic of the highest product. Sweet cream butter lacks flavour and aroma, having inde

result, various biproducts of decomposition arise, and it is these biproducts of decomposition that make the difference between the ripened and the unripened cream. They render it sour and curdle it, and they also produce the flavours and aromas that characterize it. Products of decomposition are generally looked upon as undesirable for food, and this is equally true of these products that arise in cream if the decomposition is allowed to continue long enough. If the ripening, instead of being stopped at the end of a day or two, is allowed to continue several day

ns and dairies, and the bacteria that are abundant and that grow in different lots of cream will not be always the same. It makes a decided difference in the character of the ripening, and in the consequent flavours and aromas, whether one or another species of bacteria has been growing in the cream. Some species are found to produce good results with desired flavours, while others, under identical conditions, produce decidedly poor results with undesired flavours. If the butter maker obtains cream which is filled with a large number of bacteria capable of producing good flavours, then the ripening of his cream will be satisfactory and his butter will be of high quality. If, however, it chances that his cream contains only the species which produce unpleasant flavours, then the character of the ripening will be decidedly inferior and the butter will be of a poorer grade. Fortunately the majority of the kinds of bacteria liable to get into the cream from ordinary sources are such as produce either good effects upon the cream or do not mat

ries are becoming more and more concentrated into large creameries, and it is a matter of a good deal more importance to discover some means by which a uniformly high quality can be insured. If a creamery which makes five hundred pounds of butter per day suffers from such an injurious ripening, the quality of its butter will fall off to such an extent as t

ls, etc., are all kept in condition of strict cleanliness, if especial care is taken particularly at the seasons of the year when trouble is likely to arise, and if some attention is paid to the kind of food which the cattle eat, as a rule the cream will not become infected with injurious bacteria. It may be taken as a demonstrated fact that these malign bacteria come from sources of filth, and the careful avoidance of all such sources of filth will in a very

de in the winter is inferior to that made in the summer months; and while this is doubtless due in part to the different food which the cattle have and to the character of the cream resulting therefrom, these differences in the flavour of the butter are also in part dependent upon the diff

BACTERIA CULTURES

nish these in pure culture and in large quantity to the butter makers, to enable them to inoculate their cream with the species of bacteria which will produce the results that they desire. For this purpose bacteriologists have been for several years searching for the proper species of bacteria to produce the best results, and there have been put upon the market for sale several distinct

f a pure culture to a mass of cream would not produce the desired effects, because the cream would be ripened then, not by the pure culture alone, but by the pure culture plus all of the bacteria that were originally present. It would, of course, be something of a question as to whether under these conditions the results would be favourable, and it would seem that this method would not furnish any means of getting rid of bad tastes and flavours which have come from the presence of malign species of bacteria. It is p

e of certain species of bacteria, upon the principle that the addition of such a large number of bacteria to the cream, even though the cream is already inoculated with certain bacteria, will produce a ripening of the cream chiefly influenced by the artificially added culture. The culture thus added, being present in very much greater quantity than the other "wild" species, will have a much greater effect than any of them. This method, of course, cannot insure uniformity. While it may work satisfactorily in many cases, it is very evident that in others, when the cream is already fille

ourable source possible-that is, from the cleanest and best dairy, or from the herd producing the best quality of cream-and allowing this cream to stand in a warm place for a couple of days until it becomes sour. The cream will by that time be filled with large numbers of bacteria, and this is then put as a starter into the vat of cr

obable that as the difficulties in the details are mastered the time will come when starters will be used by our butter makers for their cream ripening, just as yeast is used by housewives for raising bread, or by brewers for fermenting malt. These starters will probably in time be furn

IA IN

the fresh cheese. This cheese is then set aside for several weeks, and sometimes for months, to undergo a process that is known as ripening. During the ripening there are developed in the cheese the peculiar flavours which are characteristic of the completed product. The taste of freshly made cheese is extremely unlike that of the ripened product. While butter ma

irregularities, nor has he possessed any means of removing them. The abnormal ripening that occurs takes on various types. Sometimes the cheese will become extraordinarily porous, filled with large holes which cause the cheese to swell out of proper shape and become worthless. At other times various spots of red or blue appear in the manufactured cheese; while again unpleasant tastes and flavours develop which render the product of no value. Sometime

gly so in Limburger cheese. When we come to study the matter of cheese ripening carefully we learn beyond question that this a priori conclusion is correct. The ripening of any cheese is dependent upon several different factors. The method of preparation, the amount of water left in the curd, the temperature of ripening, and other miscellaneous factors connected with the mechanical process of cheese manufacture, affect its character. But, in addition to all these factors, there is undoubtedly another one, and that is the number and the character of the bacteria that chance to be in the curd when the cheese is made. While it is found that cheeses which are treated by different processes will ripen in a different manner, it is also found

bacteria from growing, and again ripening is found to be absolutely prevented. Furthermore, if the cheese under ordinary conditions is studied during the ripening process, it is found that bacteria are growing during the whole time. These facts all taken together plainly prove that the ripening of cheese is a fermentation due to bacteria. It will be noticed, however, that the conditions in the cheese are not favourable for very rapid bacterial growth. It is true that there is plenty of food in the cheese for bacterial life, but the cheese is not very moist; it is extremely dense, being subjected in all cases to more or less pressure. The penetration of oxygen into the centre

ctice as it seems to be in theory. Many different species of bacteria have been separated from cheeses. One bacteriologist, studying several cheeses, separated about eighty different species therefrom, and others have found perhaps as many more from different sources. Moreover, experiments have been made with a considerable number of these different kinds of bacteria to determine whether they are capable of producing normal ripening. These experiments consist of making cheese out of milk that has been deprived of its bacteria, and which has been inoculated with large quantities of the species in question. Hitherto these experiments have not been very satisfactory. In some cases th

s, and enough has been done in this line to demonstrate beyond peradventure that the abnormal ripening of cheese is due primarily to the growth of improper species therein. Quite a long list of species of bacteria which produce abnormal ripening have been isolated from cheeses, and have been studied and experimented with by bacteriologists. As a result of this study of abnormal ripening, there has been suggested a method of partially controlling these-remedying them. The method consists simply in testing the fermenting qualities of the milk used. A small sample of milk from different dairies is allowed to stand in the cheese factory by itself until it undergoes its normal souring. If the fermentation or sourin

the ripening, it would seem to be possible to obtain the proper kind of bacteria and to furnish them to the cheese maker for artificially inoculating his cheese, just as it has been possible to furnish artificially cultivated yeasts to the brewer, and as it has become possible to furnish artificially cultivat

lutely dependent; and when our bacteriologists are able in the future to investigate this matter further, it seems to be at least possible that they may obtain some means of enabling the cheese maker to control the ripening accurately. Not only so, but recognising the great variety in the flavours of cheese, and recognising that different kinds of bacteria undoubtedl