PATHOGENIC SPIRILLA. 597 
and Riedel show that it also multiplies to some extent in sterilized 
river or well water, and that it preserves its vitality in such water 
for several months. But in milk or water which contains other bac- 
teria it dies out in a few days. Gruber and Schottelius have shown, 
however, that in bouillon which is greatly diluted the cholera spiril- 
lum may take the precedence of the common saprophytic bacteria, 
and that they form upon the surface of such a medium the charac- 
teristic wrinkled film. Koch found in his early investigations that 
rapid multiplication may occur upon the surfce of moist linen, and 
also demonstrated the presence of this spirillum in the foul water of 
a “tank” in India which was used by the natives for drinking 
purposes. In the experiments of Bolton (1886) the cholera spirilluam 
was found to multiply abundantly in distilled water to which 
bouillon was added in the proportion of fifteen to twenty-five parts 
in one thousand. 
The thermal death-point of the cholera spirillum in recent cul- 
tures in flesh-peptone-gelatin, as determined by the writer (1887), is 
52° C., the time of exposure being four minutes ; a few colonies only 
developed after exposure to a temperature of 50° for ten minutes. 
In Kitasato’s experiments (1889) ten or even fifteen minutes’ expo- 
sure to a temperature of 55° C. was not always successful in destroy- 
ing the vitality of the spirillum, although in certain cultures exposure 
to 50° for fifteen minutes was successful. He was not, however, 
able to find any difference between old and recent cultures as regards 
resistance to heat or to desiccation. In a moist condition this spiril- 
lum retains its vitality for months—as much as nine months in agar 
and about two months in liquefied gelatin. Itis quickly destroyed 
by desiccation, as first determined by Koch, who found that it did 
not grow after two or three hours when dried in a thin film on a 
‘glass cover. In Kitasato’s experiments (1889) the duration of vital- 
ity was found to vary from a few hours tv thirteen days, the differ- 
ence depending largely upon the thickness of the film. When dried 
upon silk threads they may retain their vitality for a considerably 
longer time (Kitasato). Very numerous experiments have been 
made to determine the amount of various disinfecting agents re- 
quired to destroy the vitality of this microérganism. We give be- 
low the results recently reported by Boer (1890), whose experiments 
were made in Koch’s laboratory. Experiments upon a culture in 
bouillon kept for twenty-four hours in the incubating oven, time of 
exposure two hours: hydrochloric acid, 1:1,350; sulphuric acid, 
1:1,300; caustic soda, 1:150; ammonia, 1:350; mercuric cyanide, 
1 :60,000 ; gold and sodium chloride, 1 : 1,000; silver nitrate, 1: 4,000; 
arsenite of soda, 1:400; malachite green, 1:5,000; methyl violet, 
1:1,000; carbolic acid, 1: 400; creolin, 1:3,000; lysol, 1:500. In 
