424 
ZOOLOGY: CHEPLIN AND RETTGER 
Proc. N. a. S. 
in the chemical composition of the diet, but also through the ingestion of 
living cultures of Bacillus acidophilus (Moro) with or without accom- 
panying carbohydrates. 
When added in sufficient amounts to the basal diet of bread and meat, 
namely 2 grams daily, lactose and dextrin caused a very pronounced 
transformation of the intestinal flora of white rats within three to six 
days, and stimulated the development of B, acidophilus to such an extent 
that it entirely dominated the flora, thus suppressing or displacing al- 
most completely all other bacterial types commonly found in the enteric 
tract. The simple flora persisted as long as the feeding of these carbo- 
hydrates was continued. B. bifidus (l^issier) occasionally increased in 
numbers under these dietary conditions, but as a rule it remained re- 
latively obscure. 
Maltose, saccharose and glucose exercised no transforming influence 
on the types of bacteria present. These results are in perfect agreement 
with those of Distaso and Schiller (1914) and Hull and Rettger (1917). 
Torrey (1919) claims, however, to have obtained a moderate increase 
in the numbers of B. acidophilus as a result of sucrose feeding in dogs. 
The most plausible explanation of the favorable influence of lactose and 
dextrin feeding on the implantation of B. acidophilus is one which rests 
to a large extent upon the fact that in the rat at least they are not com- 
pletely absorbed before they reach the large intestine. Here they estab- 
lish an optimum environment by serving as a readily available source of 
energy for B. acidophilus. This theory was advanced by Hull and Rettger 
who found a direct relationship between the rapid development of B. 
acidophilus and the presence of a reducing substance in the contents of the 
colon and rectum after lactose feeding. These findings have been con- 
firmed in the present investigation, not only in connection with the 
administration of lactose but also dextrin. No reducing substances 
could be detected, however, after the feeding of maltose, sucrose or 
glucose. 
The stimulating influence of lactose and dextrin on the development of 
aciduric organisms in the intestine does not depend upon increased acidity 
of the intestinal contents, as hydrogen ion concentration determina- 
tions made on the fecal material of the caecum and colon of rats receiving 
these carbohydrates showed. The hydrogen ion concentration limits 
remained essentially the same during the preliminary and the transforming 
periods of the different experiments. 
The feeding of 1 gram of lactose or dextrin daily to white rats brought 
about a partial transformation which never amounted to more than 50% 
of the entire flora. These results are in harmony with the findings of 
Hull and Rettger (1917) who likewise demonstrated that 2 grams of 
lactose are necessary to cause a complete transformation. They showed 
