GROWTH OF BACTERIA IN NORMAL MILK. I 5 



decidedly injurious if these small numbers were pathogenic 

 types. We have shown in previous work* that in cream which 

 is a few hours old the large proportion of the bacteria present 

 are lactic organisms, so large a proportion that the lactic bac- 

 teria are sometimes regarded as the normal bacteria of milk. 

 There is at the present time much evidence for believing that 

 the lactic bacteria, so far from being a detriment to the whole- 

 someness of the milk, are really advantageous. It is true that 

 they cause the milk to sour if they become too abundant; 

 but the acid that they produce in milk protects the milk from 

 other fermentations which are probably more injurious. It is 

 very probable that putrefactive changes which take place in 

 milk if the lactic organisms are not present are more injuri- 

 ous to health than the development of lactic acid. Lactic 

 acid in itself is not injurious in small quantities, and there is 

 no reason for believing that the presence of lactic bacteria in 

 milk, even in considerable numbers, will, to any appreciable 

 extent, detract from the healthfulness of the milk. On the 

 other hand, there is good reason for believing that the putre- 

 factive changes in milk which other types of bacteria produce, 

 if they have an opportunity of developing therein, will be quite 

 likely to result in intestinal disturbances. It is at least a prob- 

 ability that much of the diarrhoeal disturbance in children is 

 due to the putrefactive fermentation of milk, and it is almost 

 certain that these are not due primarily to lactic bacteria. 

 Indeed, it has been shown by Bienstockf that the lactic bac- 

 teria are probably useful in the intestine. If they' are absent 

 from the intestines of animals the intestinal contents are quite 

 sure to undergo an offensive putrefactive fermentation, while 

 the presence of either lactic bacteria or the common B. coli 

 prevents the putrefactive condition of intestinal digestion. 

 These experiments of Bienstock have not as yet been con- 

 firmed, but they are quite in accordance with the general con- 

 clusion which has been reached by several observers, that the 

 presence of lactic organisms in milk prevents putrefactive fer- 

 mentation, and that these bacteria should therefore be looked 

 upon as a protection to the milk from the standpoint of its 

 wholesomeness, rather than as injurious in their action. 



*vStorrs Expt. vSta. Rept. 1900. 

 t An. d. 1. Inst. Past. XIV. p. 750. 



