6 BULLETIN 319, U. S. DEPARTMENT OF AGRICULTURE. 
ment has resulted from the ingestion of milk cultures made from it. 
It is by no means certain, however, that the results which have been 
obtained by the use of milk cultures have been attributable to any 
peculiar virtue in the organism itself. It has been held by some inves- 
tigators that the intestinal flora may be radically changed by a funda- 
mental change in the diet. 
Distaso and Schiller (19) state that when rats were fed a diet of 
lactose and dextrine the heterogeneous intestinal flora was changed 
to one consisting almost exclusively of Bacillus biftdus, the character- 
istic acid-forming bacillus of the intestines. This is in accord with 
the earlier work of Herter and Kendall (13), who found that the 
nature of the bacterial flora of the mtestines could be promptly and 
distinctly changed by a radical change from a diet high in protein 
to one in which carbohydrates predominated, or vice versa. A high- 
protein diet caused symptoms of intestinal putrefaction. A change 
to a carbohydrate diet resulted in a reduction of the putrefactive bac- 
teria, an increase in the acid-forming bacteria, and the disappearance 
of the indications of autointoxication. Similar results were ob- 
tained in an investigation carried on by Eettger (71). 
This work was very comprehensive, covering a long series of ex- 
periments with chickens and white rats, and the results if accepted 
will make it necessary to revise the commonly accepted views of the 
physiological actions of sour milk. Eettger found that when chicks 
were fed milk not only was the per cent of mortality materially re- 
duced, but the rate of growth was greatly increased. Practically the 
same results were obtained whether sweet or sour milk was fed, and 
there was no appreciable difference in the results obtained by feeding 
milk soured by Bacillus bulgaricus and the common lactic forms. 
The probable explanation of this fact was found in the experiments 
with white rats, in which a study was made of the intestinal bacterial 
flora during the feeding experiments. It was found that when the 
rats were fed a diet which included milk, the usual mixed bacterial 
flora of the intestines was replaced almost completely by two types 
of bacteria which resemble the Bacillus bulgaricus very closely, espe- 
cially in their physiological characteristics. Identical results were 
obtained when the milk was displaced in the diet by milk sugar. 
The conclusion seems obvious. The bacteria of the high-acid type, 
which are apparently normally present in the intestines, are stimu- 
lated by the unusual amount of milk sugar furnished by the milk 
diet, and multiply to such an extent that the ordinary mixed flora is 
suppressed. 
The beneficial effect of a sour-milk diet is attributable, perhaps, not 
so much to the bacteria contained in the milk as to the milk itself, 
which provides material for an acid fermentation in the intestines. 
