PATHOGENIC BACTERIA IN DIFFERENT WATERS 309 



for some time, yet the vitality of the latter is by no 

 means extinguished, for if the struggle between the two 

 be sufficiently protracted, until the process of putre- 

 faction is less active, the presence of the comma 

 bacilli can be again readily demonstrated by cultiva- 

 tion. It is necessary, therefore, to exercise consider- 

 able caution in judging upon this point in the present 

 state of our knowledge, and it would be highly pre- 

 mature to place too much reliance upon this alleged 

 destruction of pathogenic forms by non-pathogenic 



ones.' 



The recent experiments of Trenkmann, moreover, 

 indicate that the preservation of the cholera bacilli in 

 unsterile water may be materially influenced by the 

 presence of salts, a circumstance which not improbably 

 may have played an important part in the distribution 

 of cholera by means of the waters of the Elbe and 

 Thames, which during some of the London cholera epi- 

 demics was supplied to the metropolis from its tidal 

 portion ; whilst in the case of shallow well-waters which 

 have given rise to outbreaks of cholera, large propor- 

 tions of salts (nitrates, chlorides, and sulphates) will 

 doubtless not have been wanting. 



1 ' Recent Bacteriological Research in connection with Water Supply.' 

 Percy Frankland, Journ. Soc. of Chein. Industry, 1887. 



