6 BULLETIN 319, U. S. DEPARTMENT OP 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 Mfidus, the character- 

 istic acid-forming bacillus of the intestines. This is in accord with 

 the earlier work of Herter and Kendall (43), who found that the 

 nature of the bacterial flora of the intestines 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 Rettger (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. Rettger 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 hulgaricus 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 hulgaricus 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. 



