SPIRILLUM CHOLERZ ASIATICZ. 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 conditions 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 ingestion 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- 
37 
