BACILLUS COLI COMMUNIS. 447 
.sesses also a considerable reducing power, converting 
nitrates into nitrites, as may be demonstrated by the 
addition of sulphuric acid in the proper proportion to 
a bouillon or peptone culture, when a pink coloration 
results. 
On Potato. On potato the growth is rapid and 
abundant, appearing after twenty-four to thirty-six 
hours in the incubator as a yellowish-brown to dark 
cream-colored deposit covering the greater part of the 
surface. But there are considerable variations from 
the typical growth on potato; there may be no growth 
at all, or it may be scanty and of a white color. These 
variations are due at times to the bacillus, but more 
often to variations in the potato. 
Gas-production. The bacillus coli grows rapidly 
in media containing glycerin and sugar, particularly 
glucose, causing active fermentation with liberation of 
carbonic acid and hydrogen gas. Cultivated in solid 
media, to which glucose has been added, the gas-pro- 
duction is recognized by the appearance of numerous 
bubbles along and about the points of growth; in fluid 
media it may be demonstrated in the fermentation-tube. 
Grown on lactose-litmus-agar, the colonies are pink 
and the color of the surrounding medium is changed 
from blue to red, showing the production of acid. 
Milk is coagulated by the growth of the bacillus 
coli after twenty-four to seventy-three hours in the in- 
cubator, with the production of gas and acid; very 
rarely acid may be produced and no coagulation occur. 
The coagulation of the milk is hastened by warming. 
The thermal death-point of the colon bacillus from 
feces was found by Weisser to be 60° C., the time of 
exposure being ten minutes. When the bacilli from 
