382 CHOLERA. 



On all the media the growth of the cholera spirillum is a 

 relatively rapid one, and especially is this the case in the 

 peptone solution named and in bouillon, a circumstance of 

 importance in relation to its separation in cases of cholera 

 (vide p. 399). 



Another characteristic, though one not peculiar to this 

 organism, is the so-called cholera-red reaction. If to a culture 

 in peptone bouillon or solution of peptone (i per cent), 

 which has grown for twenty-four hours at 37 C, a few drops 

 of pure sulphuric acid are added, a reddish-pink colour is 

 produced. This is due to the fact that indol and a nitrite 

 are formed by the spirillum in the medium. The addition 

 of sulphuric acid causes a nitroso-indol body to be produced 

 from these, and this gives the red colour. It is to be noted 

 that, unlike the case of the B. coli communis where a similar 

 reaction occurs, the addition of a nitrite is here unnecessary, 

 as the nitrite is formed by the organism, probably from the 

 nitrates which are present. Here, as in the case of the 

 negative indol reaction given by the typhoid organism, it is 

 found that not every specimen of peptone is suitable, and it 

 is advisable to select a peptone which gives the characteristic 

 reaction with a known cholera organism, and to use it for 

 further tests. It is also essential that the sulphuric acid 

 should be pure, for if traces of nitrites are present the 

 reaction might be given by an organism which had not the 

 power of forming nitrites. This is one of the most important 

 tests in the diagnosis of the cholera organism. It is always 

 given by a true cholera spirillum, and though the reaction is 

 not peculiar to it, the number of organisms which give the 

 reaction under the conditions mentioned are comparatively 

 few. 



The cholera organism is one which grows much more 

 rapidly in the presence of oxygen than in anaerobic con- 

 ditions. Koch, in his earlier work, believed that no growth 

 took place in the absence of oxygen, and it has been 

 recently stated that this is the case in absolutely anaerobic 

 conditions. Growth, however, takes place in the ordinary 

 anaerobic conditions, usually employed in the culture of 



