102 UNIVERSITY OF WISCONSIN STUDIES 
B. coli is of a similar nature, but the primary and secondary 
fermentations proceed at different rates and the end products 
are different from those produced by B. acrogenes. (2) With 
this are correlated various other characters, particularly a 
higher percentage of indol formers in B. coli and the forma- 
tion of acetyl-methyl-carbinol by B. aerogenes. (3) There is 
also correlated with these physiological differences a difference 
in habitat. B. coli is the characteristic gas-forming organism 
cf animal feces and is commonly found elsewhere only in 
localities recently contaminated with fecal matter. B. aero- 
genes and B. cloacae, on the other hand, occur rarely in bovine 
feces and in relatively small numbers in human feces, but are 
common in soil and materials contaminated with soil. 
B. coli is probably of specifie rank and the subdivisions 
usually made on the basis of saecharose fermentation should 
not be looked upon as more than varieties of doubtful validity. 
It is possible to make two similar varieties of B. aerogencs on 
the basis of the fermentation of adoritol. This character is 
givcn an added significance by a high correlation with habitat. 
All of the aerogenes cultures from feces fermented adonitol 
while a large percentage of those from grains were adonitol 
negative. 
The distinction between B. acrogceues and B. cloacae, beyond 
the liquefaction of gelatin, is not very sharp, but everything 
considered B. cloacne should be a separate species. 
A small group of cultures distinguished by the liquefaction 
of gelatin, the fermentation of dextrose with the formation 
of CO, only, and the fermentation of saccharose but usual 
failure to ferment lactose is evidently identical with B. pro- 
teus. The failure to ferment lactose, usually considered 
the distinguishing character of B. proteus, does not coincide 
perfectly with the more fundamental character indicated by 
the single gascous end product of the fermentation. The 
unusual colony formation commonly looked upon as peculiar 
to proteus is probably shared with some B. cloacae cultures. 
A more logical separation between B. proteus and B. cloacae 
would be on the end products of the fermentation rather than 
on the nature of the material fermented. 
