SPIRILLUM CHOLERA ASIATICS. 577 



tained in small quantities in the culture media; and 

 showed that it is the setting free of nitric acid, upon 

 the addition of sulphuric acid to the culture, which 

 gives with indol the red body upon which the cholera 

 reaction depends. For a long time it was believed that 

 this nitroso-indol reaction was peculiar to the cholera 

 bacillus, and great weight was placed on it as a diag- 

 nostic test. It has since been shown, however, that 

 there are a number of other vibrios which, under sim- 

 ilar conditioDS as the cholera vibrio, give the same red 

 reaction. The reaction is, nevertheless, 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 suspected organism that 

 it is not the cholera spirillum. There are, however, 

 certain precautions to be observed in its use. It has 

 been shown that the reaction may be absent, for in- 

 stance, when the culture contains either too much or 

 too little nitrate. It is, therefore, advisable not to em- 

 ploy 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 solution). With 

 such a solution constant results can be obtained. 



Pathogenesis. Since none of the lower animals is nat- 

 urally subject to cholera, nor has ever contracted the 

 disease during the prevalence of an epidemic or as the 

 result of the iugestion of food contaminated with chol- 

 eraic excreta, there is no reason to expect that inocula- 

 tions of pure cultures of the spirillum, either subcuta- 

 neously or by the mouth, will give rise in animals to a 

 typical attack of cholera. It has been shown, more- 



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