46 WATER 



saves time, but not labour, is to directly test every suspicious 

 and possible colony with powerful anti-cholera serum. All the 

 vibrios which are agglutinated are subcultivated and their cultural 

 characters and serological properties tested in detail. 



Houston 1 in his investigations upon the vitality of cholera 

 vibrios in water and their isolation therefrom used agar, bile- 

 salt agar and Drigalski-Conradi agar. The bile salt however 

 considerably inhibits growth and only very small red colonies 

 are produced by the cholera vibrio. 



If a large number of possible colonies have to be sorted out, 

 it is essential to have a few cultural tests which rapidly eliminate 

 the majority of those which are not cholera vibrios. Houston's 

 procedure was to subcultivate all possible colonies into saccha- 

 rose peptone water in double tubes. Only those which showed 

 acid without gas formation after 24 hours at 37 C. were further 

 investigated. Other important eliminating tests used by him 

 were growth in peptone water (for cholera-red reaction) and 

 upon gelatine slope. Failure to give a cholera-red reaction in 24 

 and in 48 hours, and rapid liquefaction of gelatine were sufficient 

 to exclude the organisms as not cholera vibrios. The organisms 

 which passed these tests were subjected to further cultural 

 investigation. 



Since a considerable number of vibrios which closely resemble 

 the true cholera organism have been found in water it is essential 

 that all available tests be employed before an organism is accepted 

 as Sp. cholerae. 



Morphological, cultural and pathogenicity tests are valuable 

 in the diagnosis of cholera vibrios but they are not sufficient in 

 themselves, and vibrios have repeatedly been isolated from water 

 which, as regards these tests, cannot be distinguished from those 

 isolated from the intestines of cholera cases but which on other 

 grounds cannot be considered true cholera vibrios. 



By the use of additional tests, particularly agglutination tests 

 and the immunity reactions of PfeifTer and of Bordet, accurate 

 differentiation can be arrived at. 



The International Office Report above referred to lays down 

 the following in regard to agglutination tests, based upon the 



1 Fourth and Fifth Research Reports, Metropolitan Water Board. 



