4 io CHOLERA. 



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. 

 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 organ- 

 ism 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 

 anaerobic organisms, such as those of tetanus and malignant 

 oedema, though it occurs more slowly than in the presence 

 of oxygen. In the intestines the oxygen supply, though 

 small in amount, is yet sufficient for the growth of the 

 spirilla. 



Powers of Resistance. In their resistance against heat 

 cholera spirilla correspond with spore-free organisms, and 

 are killed in an hour by a temperature of 55 C, and much 

 more rapidly at higher temperatures. They have com- 

 paratively high powers of resistance against great cold, 



