BACILLUS COLI COMMUNIS. 451 
by experiment that 1 c.c. of a fresh bouillon culture 
of the B. coli from normal feces was required to kill 
guinea-pigs by intraperitoneal and rabbits by intraven- 
ous injection, whereas less than one-fifth as much of a 
culture from a fatal case of cholera nostras was suf- 
ficient to kill the same animal; but this rule has prob- 
ably many exceptions, even if it be true in some cases. 
All observers, however, agree that the virulence 
of the B. coli is diminished by continued cultivation 
through successive generations, and that it is increased 
by passage through animals. 
Immunization. Immunization against colon infec- 
tion is comparatively easy to produce in the usual way 
by the inoculation of gradually increasing doses of 
cultures of the living bacilli or dead bacilli. 
Occurrence in Man and Animals. The bacillus coli 
communis is a common inhabitant of the intestinal 
canal in man and in many animals. According to 
Fremlin, it is found normally in dogs, mice, and rab- 
bits, but not in rats, pigeons, or guinea-pigs. Accord- 
ing to Dyas and Keith, it occurs in goats, rabbits, dogs, 
cats, swine, and cows, but not in horses. Grimbert 
claims to have found it in the intestines of almost all 
domestic animals, and in the mouth as well as the in- 
testines of man. It is also frequently found in water 
and food (milk, etc.), so that it is one of the most wide- 
spread saprophytic bacteria known. Formerly it was 
thought that the presence of the B. coli in water was 
sufficient proof of its contamination by feces; but the 
recent investigations of Weichselbaum, Kruse, Beck- 
mann,.and Refith would seem to show that there are 
no grounds for this assumption, as the colon bacillus 
may reach the water from many different sources. 
