426 ZOOLOGY: CHEPLIN AND RETTGER Proc. N. A. S. 
feces or from any portion of the digestive tract, whether the organism 
was fed alone or together with a utiHzable carbohydrate. The contention 
of Metchnikoff and his followers that B. bulgancus lends itself readily to 
implantation in the digestive tract of man receives no support whatever 
from the present observations upon white rats. 
Although considerable doubt must be cast upon Metchnikoff's ex- 
planation of the merits of the sour-milk therapy, we may be compelled 
to accept the fundamental principle of his arguments. That is, bacterial 
implantation with the concomitant transformation of the intestinal 
flora, is without doubt, both desirable and possible, but it is possible only 
when living cultures of properly qualified organisms are employed, or 
when such specific diets are administered which will stimulate and favor 
such a transformation. B. bulgancus is not of intestinal origin and is 
incapable of accommodating itself to intestinal conditions. B. acidophilus, 
on the other hand, is of intestinal origin and has shown itself to submit 
readily to implantation in the intestine of the white rat at least. 
In many of the experiments of Metchnikoff and his pupils large quan- 
tities of milk were consumed as milk cultures of B. hulgaricus. Hull and 
Rettger showed that milk, when given in sufficient amounts to rats causes 
a rapid development of B. acidophilus in the intestine which may result 
in the complete suppression of other forms of bacteria. These observa- 
tions were confirmed in the present investigations, not only for rats but 
also in numerous milk-feeding experiments on man. Milk owes this 
property to the lactose. It is not at all unlikely that what Metchnikoff 
and his pupils regarded as B. hulgaricus in the feces of animals and of 
human subjects was in reality B. acidophilus. These two organisms 
resemble each other so closely that one may easily be mistaken for the 
other. The above assumption is strengthened further by the statement 
of Belonowsky (1907) that the intestinal flora of nursing mice was of the 
same character as that of the older mice receiving the B, hulgaricus (milk) 
culture. 
The feeding of B. hulgaricus without due regard to the use of milk can 
have little or no importance attached to it. The beneficial results which 
have been attributed to yogurt and other oriental sour-milk products 
have in all probability been due to the milk as such, rather than to the 
acid-producing bacteria contained in these products. 
For a full account of the present investigation the reader is referred 
to the doctorate thesis of Harry A. Cheplin in the Yale University 
Library. The methods and results of these experiments, together with 
those conducted oil man, will be published at an early date in unabridged 
form. 
