1 88 BACTERIOLOGY. 



Massowah especially are to be separated from 

 cultures of cholera germs obtained in European 

 epidemics. 



In peptone solutions the bacteria produce 

 indol and also reduce nitrate to nitrite ; conse- 

 quently on the addition of hydrochloric or sul- 

 phuric acid the nitroso-indol reaction takes 

 place in the form of a rose-red coloration which 

 has been named the " cholera-red " reaction. 

 In ordinary bouillon a pellicle is formed on the 

 surface, in glucose-bouillon this does not occur. 

 On potato at high temperatures a yellowish- 

 brown pigment is formed ; in milk a rennet- 

 like separation into curd and whey is some- 

 times produced. The differential diagnosis of 

 cholera has become very difficult becatise many 

 comma bacilli have been found which grow in 

 gelatin and bouillon very much like the typical 

 and atypical varieties of cholera bacteria. 



In the lower animals, no spontaneous cases 

 of any disease caused by Koch's cholera bacteria 

 'have ever been observed ; when inoculated 

 artificially, however, virulent germs prove infec- 

 tious for guinea-pigs and often also for pigeons ; 

 in the latter animals the toxic disease passes 

 into a septicsemic. Another comma bacillus 

 nearly related to Koch's, which was found by 

 Gamaleia in a fowl epidemic and named after 

 Metschnikoff , is infectious for animals ; pigeons 



