CHARACTERISTICS OF THE COLON-AEROGENES GROUP 101 
evidence supporting or controverting this theory. If the 
loss of ability to ferment adonitol is effected only after many 
generations under the new conditions, it is only another way 
of saying that a variety has been created by a change of en- 
vironment. If the change takes place in the original cells, 
it may be considered as an indication of the remoteness of the 
contamination. 
While none of the liquefying cultures in this collection 
were isolated from feces there is no doubt that they occur 
there under certain circumstances. Ford*®® reports the oc- 
currence of B. cloacae in feces. Clemesha* says that B. clo- 
acae may be present in human feces in numbers as high as 
15 or 20 per cent of the total. MacConkey* found occasional 
gas forming liquefiers in feces. On the other hand, nearly 
one half of the coli-like organisms isolated from soil by John- 
son and Levine*®* were liquefiers. Unless we assume that the 
liquefiers of this group are more resistant to unfavorable con- 
ditions than the other types and therefore persist longer in 
water and in the soil it is evident that the principal source 
of B. cloacae and B. proteus is outside of the intestinal tract. 
CoNCLUSIONS 
It may be considered as established by the results reported 
here, supported as they are by the observations of many 
other investigators, that B. coli (low ratio) and B. aerogenes 
(high ratio) are very distinct types. This is based on: (1) 
a fundamental difference in the course of the fermentation. 
Carbohydrates are fermented more readily by B. aerogenes 
and B. cloacae with a secondary rapid fermentation of the 
by-product, resulting in a greater production of CO, and a 
decrease in acidity.. The fermentation brought about by 
%°W. W. Ford, Classification of Intestinal Bacteria in Jour. Med. Res., 
6, 1, pp. 211-219, 1901. 
"1°W. W. Clemesha, The Bacteriology of Surface Waters in the Tropics, 
London, 1912. 
32 Alfred MacConkey, Further Observations on the Differentiation of Lac- 
tose-fermenting Bacilli with Special Reference to those of Intestinal Origin 
in Jour. Hyg., 9, 1, pp. 86-103, 1909. 
%3 Loc. cit. 
