CHAPTER V. 



THE ISOLATION OF SPECIFIC PATHOGENES FROM 

 WATER. 



THE discovery of the organisms which specifically cause 

 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 either to use media, which 

 especially 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 check- 

 ing the development of the common water bacteria. It 

 was apparent that the body temperature and the presence 

 of a slight excess of free acid furnished such conditions, 

 and most of the methods suggested rest upon these prin- 

 ciples. Among these, one of the earliest was that of Parietti 

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

 of the water to a series of broth tubes containing increasing 



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