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 hulgaricus, 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 hulgaricus. 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 hulgaricus 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. hulgaricus 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. hulgaricus, 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 
