84 THE MILK QUESTION 



even in adults. Many instances have been recorded in 

 which it is asserted that such milk has caused the poison- 

 ing of large numbers of people. In such cases it is doubt- 

 ful whether the trouble is due to a chemical poison formed 

 in the milk, for in the case of meat poisoning, or so- 

 called ptomaine poisoning, we know the symptoms are 

 really the result of a bacterial infection, and are not the 

 result of toxines or ptomaines. 



The ordinary souring of milk is, therefore, a conservative 

 process, and is sometimes known as nature's danger signal. 

 It is really not a danger signal at all, for sour milk, butter- 

 milk, koumiss, and other forms of fermented milk are a 

 very good and nutritious food, sometimes even for delicate 

 babies. Fermentation, far from being a danger signal in 

 milk, is rather a flag of truce or safety device which pre- 

 vents or retards the development of poisonous properties. 



Fermented milk is acid in reaction, has a sour smell, 

 shows the well-known curd, which consists of precipitated 

 casein, and is not particularly harmful. On the other hand, 

 putrid milk is more alkaline in reaction, has a disagreeable, 

 even disgusting odor and taste. The curd is gelatinous and 

 undergoes self-digestion, while the products of the putre- 

 factive process may be harmful. 



The particular micro-organisms which produce fermenta- 

 tion are known as lactic acid organisms. There are many 

 different varieties. The principal ones are the Bacillus 

 acidi lactici of Hueppe, the Bacillus lactis acidi of Leich- 

 mann, the Streptococcus lacticus of Kruse, and, in addition 

 to this, sometimes other organisms, such as the Bacillus 

 cerogenes, the common colon bacillus, the Bacillus 

 bulgaricus of Metchnikoff, various streptococci, etc. The 

 cause of the souring is the conversion of the milk sugar into 

 lactic acid due to the bacterial action. The bacteria which 

 cause the normal souring of milk for the most part get into 

 the milk with the dirt. Milk that is obtained with scru- 

 pulous care will not contain the lactic acid organisms in 



