2 74 



SCIENCE. 



[Vol. XVII. No. 432 



We will now pass on to the second division of our subject, and 

 ask what is the cause of these fermentations. The alcoholic fer- 

 mentation and that of rennet may now be omitted from discus- 

 sion, for every one knows that these are produced by adding 

 something to the milk, a yeast in the one case, and rennet in the 

 other. Leaving aside these, then, we would naturally expect, in- 

 asmuch as the other fermentations are very varied, to find their 

 causes varied also. In a certain sense this is true, but at the 

 same time there is one point in which they all agree. All of the 

 fermentations mentioned above are due to microscopic plants get- 

 ting into the milk subsequent to the milking and their growing. 



Before passing to a further consideration of this matter, it may 

 be well to notice that there occurs, very rarely, a curdling of milk 

 which is not due to micro-organisms. Once in a while milk is 

 found to curdle almost as soon as it is drawn from the cow, and 

 in this case the trouble is not due to micro-organisms. Such an 

 occurrence is extremely rare, liowever, and it is doubtful whether 

 any of you have ever had any experience with it. But aside 

 from this rare occurrence, all of the fermentations are caused 

 either by bacteria or yeasts, which get into the milk subsequent to 

 the milking. 



It has taken many years to reach this conclusion. It will be 

 convenient for us to consider the fermentations as belonging to 

 two classes, one of which we may call the normal fermentations, 

 and the other the abnormal fermentations. The former class in- 

 cludes only the common souring and the rennet fermentations, 

 while the abnormal class includes all of the others. Now it has 

 been recognized from the very earliest times that the abnormal 

 fermentations were due to something getting into the milk which 

 did not belong there. So long ago as 1838 a microscopic study of 

 blue milk revealed in it some micro-organisms, and these were 

 even then suggested as the cause of the trouble. From that time, 

 as one after another kind of fermented milk was studied, it was 

 seen that they were all associated with some form of bacteria, and 

 the conclusion is now very definitely proved that they are all 

 caused by these organisms. AH of the forms of fermentation 

 mentioned above have been associated with definite species of 

 bacteria, and all can be artificially produced by inoculating good 

 milk with the right species of bacteria. 



After it was seen that bacteria were the cause of the troubles, 

 the nest question was to account for their presence in the milk. 

 It did not seem possible at first that they could all get into the 

 milk after the milking. All sorts of explanations were suggested 

 relating to conditions surrounding the cow. The cow was sup- 

 posed to have caught cold, or to have been heated, or to have run 

 too fast, or to have been eating some injurious kind of food, and 

 for some of these reasons the milk fermented. Every thing was 

 blamed except the carelessness of the milker. I imagine that 

 many of you even to-day think you have very good reason for 

 believing that certain fermentations are really caused by the food 

 that the cow eats, and this has always been the favorite excuse. 

 You have, perhaps, found slimy milk in your dairy, and have 

 then remembeied that recently you begun to feed your cow on a 

 special lot of meadow hay. Thinking that this might have caused 

 the trouble, you ceased to feed this hay and the trouble ceased. 

 What better proof could you desire that it was the hay that the 

 cattle ate which produced the slimy milk ? In fact nothing of the 

 sort is proved by this experiment. Do you not remember that 

 when ensilage was first introduced, many farmers complained of 

 it, saying that its use caused their milk to become tainted, and 

 thus much injured its quality? And do you not also remember 

 that as experience began to accumulate it soon appeared that it 

 was not the ensilage which the cows ate which produced the 

 trouble but the ensilage which the milker handled ? To-day you 

 know that you can feed ensilage to the cow with no danger pro- 

 vided that you exercise suflHcient care in handling it, and allow 

 no opportunity to occur for the ensilage to contaminate the milk 

 after the milking. So it is with all other ferments. It is not the 

 food that the cow eats that produces the fermentation, but it may 

 . be the food that is in the barn, and is being constantly stirred up 

 so as to keep the air full of floating bacteria. These may get 

 into the milk and produce trouble, and they will be avoided by 

 letting the hay alone or doing the milking out of the proximity 



of this troublesome food. The cow may eat it with impunity. 

 The remedy is not to change the food but the conditions of the 

 milking-yard and the dairy. 



Do not understand that I would infer that the food the cows 

 eat has no influence on the taste of the milk. There is no ques- 

 tion that if the cows eat a strong-tasting food like garlic, the taste 

 is transferred to the milk. But this is a very different thing from 

 the production of fermentation. The taste produced by such food 

 is at its maximum as soon as the milk is drawn, while in the case 

 of a fermentation the effect is an increasing one, being absent at 

 flrst, but appearing as the bacteria have chance to grow. 



While thus it is seen that the unusual fermentations have long 

 been ascribed to the action of bacteria or something else getting 

 into the milk which does not belong there, this has by no means 

 always been supposed to be true of the common souring of milk. 

 The souring is a universal and not an occasional thing, and there 

 seemed for a long time to be no way to prevent it. So long ago 

 as 1844 bacteria were found in souring mUk, and it was even then 

 suggested that the souring was due to them. In ISSO again the 

 fact was reaflirmed. Pasteur commenced his work on milk about 

 1860, and finding that he could prevent the souring by subjecting 

 the milk to a high heat, and, moreover, being always able to dis- 

 cover in it numerous bacteria, he insisted that even this common 

 fermentation was due to these organisms. The statement did not 

 go unchallenged, however, and for the next ten years there were 

 conflicting results. In 1874, and later. Lister and Hall succeeded 

 in procuring milk directly from the cow with such precautions as 

 to avoid chance of contamination by bacteria, and they found 

 that such milk remained sweet indefinitely without showing any 

 tendency to undergo even the souring fermentation. After this 

 there could no longer be any question in regard to the matter, and 

 we may therefore ascribe the souring of milk to the same class of 

 causes as those producing the more unusual fermentations. 



It may seem somewhat remarkable that bacteria should so uni- 

 versally get into milk. But the fact is that they are very abundant 

 everywhere. They are in the air, in the milk vessels, on the hands 

 of the milker, on the hairs of the cow, and above all they wiU be' 

 inside of the milk duct, extending for a short distance from its 

 mouth. Some milk will always be left in the mouth of the duct, 

 and in this milk the bacteria will grow and i-emain there ready to 

 contaminate the next milk that comes out. The number of bac- 

 teria in milk is very great, and I can hardly believe the figures 

 which are indicated by ray own experiments. I have found in 

 milk which has been only two or three hours drawn from the cow 

 as many as 20,000 to 40,000 to each teaspoonful of milk. These 

 numbers are surprising, but they are not so large as have been 

 found by certain German experimenters. In milk that has been 

 standing for a little while they increase wonderfully, so that by 

 the time the milk reaches the city their number is prodigious. I 

 suppose no one in a city ever gets milk to drink that contains a 

 smaller number of bacteria to the teaspoonful than there are in- 

 habitants in the United States according to the last census. 



We are now ready to pass to the third head of the subject, the 

 prevention of the fermentations. As I stated at the outset, I have 

 no royal prevention to recommend for this, and can hope only to 

 throw out some suggestions which each may apply to its own 

 special troubles. We may set aside the fermentations produced 

 by rennet, and the alcoholic fermentations, because these are always 

 produced by adding something to the milk, and may therefore be 

 easily prevented. 



Now, if all other fermentations are due to the growth of bac- 

 teria, we have only to keep them out of the milk in order to pre- 

 vent them. This is, however, entirely impracticable. The bacteria 

 are so abundant, and they lurk in so many places, that no practi- 

 cal method can be adopted to prevent them from getting into the 

 milk. Especially is this true of the souring species. We find that 

 the souring of milk is produced by a number of species of bacteria, 

 and these are marvellously numerous about the barn, and more 

 particularly in the dairy. Perhaps care may lessen their number, 

 but it cannot do away with them altogether. 



This is not true, however, with regard to the bacteria which pro- 

 duce what I have called the abnormal or unusual fermentations. 

 The bacteria which produce slimy milk, bitter milk, blue milk, 



