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 surface 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 spirillum 

 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. It is 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 to 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 microorganism. 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 



