576 BACTERIOLOGY. 
tion. In these they occurred only in involution 
forms. 
The comma bacillus is killed by exposure to moist 
heat at 60° C. in ten minutes. The bacilli have been 
found alive in ice kept for a few days, but ice which 
has been preserved for several weeks does not contain 
living bacilli. 
Chemical disinfectants readily destroy the vital- 
ity of cholera vibrios. For disinfection on a small 
scale, as for washing the hands when contaminated with 
cholera infection, a 0.1 per cent. solution of bichloride 
of mercury or a 2 to 3 per cent. solution of carbolic acid 
may be used. For disinfection on a large scale, as for 
the disinfection of cholera stools, strongly alkaline milk 
of lime, according to Pfuhl’s experiments, is an excel- 
lent agent. The wash of cholera patients, contaminated 
furniture, floors, etc., may be disinfected by a solution 
of 5 per cent. carbolic acid and soap-water. The dis- 
infecting action of mineral acids, particularly of sul- 
phuric acid, has been advantageously employed for the 
disinfection of entire systems of water-works into which 
cholera bacilli had gained access. 
Pohl, Bujivid, and Dunham have shown that when 
a small quantity of chemically pure sulphuric acid is 
added to a twenty-four-hour bouillon culture of the 
cholera bacillus containing peptone a reddish-violet 
color is produced. Brieger separated the pigment 
formed in this reaction—the so-called cholera-red—and 
showed that it was indol, and that the reaction was 
nothing more than the well-known indol reaction. Sal- 
kowski and Petri then demonstrated that the cholera 
bacilli produced in thin bouillon cultures, along with 
indol, nitrites by reduction from the nitrates con- 
