4 BULLETIN 319, U. S. DEPARTMENT OF AGRICULTURE. 



acetic acid produced by a bacterial fermentation; when milk sours 

 spontaneously, the acid-forming bacteria develop acid so rapidly 

 that in a short time all other bacteria are inhibited. Observations 

 of this kind could be multiplied almost indefinitely. In fact, in the 

 bacterial world, as among the higher plants in their natural state, 

 there is a constant struggle for mastery in which the types best 

 suited to their environments, or, perhaps more correctly, less sensi- 

 tive to the unfavorable conditions which they themselves produce, 

 gain the ascendency and more or less completely suppress other 

 forms. 



The particular bacterium which it is proposed to use in suppressing 

 the putrefactive bacteria of the intestines is the organism commonly 

 known as Bacillus bulgaricus, or the Metchnikoff bacillus. It is 

 characterized by its ability to form acid in exceptionally large 

 amounts from sugars, particularly milk sugar. 



When milk containing bacteria of this type is held under condi- 

 tions favorable to its growth, the acid produced will inhibit other 

 forms and the milk will eventually become a practically pure culture 

 of the Bacillus bulgaricus. There can be no question that, under 

 conditions favorable to its growth, this bacterium is able to sup- 

 press very effectively other kinds of bacteria, even many of those 

 which produce an acid fermentation. This is well illustrated in the 

 manufacture of cheese of the Emmental or Swiss type. Cheese 

 made by this method from milk containing gas-forming bacteria 

 will become filled with gas bubbles in the press. If a comparatively 

 small amount of a culture of the Bacillus bulgaricus is added to this 

 milk the high temperature at which the cheese is held promotes its 

 vigorous development, and the gas formers are completely sup- 

 pressed. 



There is little doubt that if this organism could be established in 

 the large intestine under conditions favorable to its growth it would 

 soon produce a state of affairs which would at least inhibit the 

 growth of the bacteria that usually decompose the proteins. The 

 evidence that this takes place, even when large quantities of the bac- 

 teria are ingested, is by no means conclusive. On the one side the 

 associates of Metchnikoff have produced considerable evidence to 

 show that when B. bulgaricus is taken into the digestive system it 

 becomes established in the intestines, where it persists for some time 

 after the feeding ceases. Cohendy (12), who fed four patients for 

 extended periods on milk curdled with B. bulgaricus, concluded that 

 this organism was readily established in the intestines and that it 

 persisted there for a considerable time after the subject had ceased to 

 take fermented milk. This was said to be especially true if a diet 

 containing suitable nourishment for the ingested organism was 

 adopted. It is stated that the multiplication of these bacteria took 



