777 /; CHOLERA SPIiUU.f.M AM) M.IJl-D VARIETIES 397 



indol reaction was peculiar to tlic cholera bacillus, and great weight was 

 ])laccd on it as a diagnostic test. It lias since been shown, however, tl at 

 there arc a number of other vibrios which, under similar condition 

 the cholera vibrio, give the same red reaction. The reaction i>, neverthe- 

 less, a constant and characteristic peculiarity of this spirillum, and is of 

 unquestionable value. It is even more valuable as a negative than as a 

 positive test, as the absence of the reaction enables one to say of a sus- 

 pected organism that it is not the cholera spirillum. There are, how- 

 ever, certain precautions to be observed in its use. It has been shown 

 that the reaction may be absent, for instance, when the culture contain.-* 

 either too much or too little nitrate. It is, therefore, advisable not to 

 employ a bouillon culture the composition of which is uncertain, but 

 a distinctly alkaline solution of peptone, containing 1 per cent, pure 

 peptone and 0.5 per cent, of pure chloride of sodium (Dunham's solu- 

 tion). With such a solution constant results can be obtained. 



DEVELOPMENT OUTSIDE OF THE BODY. It has been shown by 

 experiment that cholera spirilla multiply to some extent in sterilized 

 river-water or well-water, and preserve their vitality in such water for 

 several weeks or even months. Koch 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 his early investigations he found 

 that rapid multiplication may occur upon the surface of moist linen. 



RESISTANCE AND VITALITY. If a culture be spread on a cover-glass 

 and exposed to the action of the air at room temperature the bacilli 

 will be dead at the end of two or three hours, unless the layer of culture 

 is very thick, in which case it may take twenty-four hours or more to 

 kill all the bacilli. This indicates that infection is not produced by means 

 of dust or other dried objects contaminated with cholera bacilli. The 

 transmission of these organisms through the air, therefore, can only 

 take place for short distances, as by a spray of infectious liquids by 

 mechanical means as, for instance, the breaking of waves in a har- 

 bor, on water-wheels, etc., or in moist wash of cholera patients. 



The cholera bacillus is also injuriously affected by the abundant 

 growth of saprophytic bacteria. It is true that when associated with 

 other bacteria, if present in large numbers, and if the conditions for 

 their development are particularly favorable, the cholera bacillus may 

 at first gain the upper hand, as in the moist linen of cholera patients, 

 or in soil impregnated with cholera dejecta; but later, after two or 

 three days, even in such cases, the bacilli die off and other bacteria grad- 

 ually take their place. Thus, Koch found that the fluid contents of 

 privies twenty-four hours after the introduction of comma bacilli no 

 longer contained the living organisms; in impure river-water they were 

 not demonstrable for more than six to seven days, as a rule. In the 

 dejecta of cholera patients they were found usually only for a few days 

 Cone to three days), though rarely they have been observed for twenty 

 to thirty days, and on one occasion for one hundred and twenty days. 

 In unsterili/ed water they may also retain their vitality for a relatively 

 longtime; thus, in stagnant well-water they have been found for eighteen 



