CHAPTER V. 



THE ISOLATION OF SPECIFIC PATHOGENES FROM 

 WATER. 



THE discovery of the organisms which specifically 

 cause the infectious diseases naturally led to the hope 

 that their isolation from polluted water might become 

 the most convincing proof of its sanitary quality. The 

 typhoid bacillus and the spirillum of Asiatic cholera were 

 in this connection of paramount importance, and to the 

 search for them many investigators devoted themselves. 



In the earlier examinations of water for the typhoid 

 bacillus an attempt was made to use media which espe- 

 cially favored the growth of the microbe sought for, or to 

 begin with some process of " enrichment " in which the 

 sample was incubated under conditions which would 

 favor the growth of the pathogenic organisms while 

 checking the development of the common water bacteria. 

 It was apparent that the body temperature and the pres- 

 ence of a slight excess of free acid furnished such condi- 

 tions, and most of the methods suggested rest upon 

 these principles. The most general perhaps is that of 

 Parietti (Parietti, 1890), which consists in the addition 

 of the water to a series of broth tubes containing increas- 



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