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 have devoted 

 themselves. 



The Search for Typhoid Bacilli. In the earlier exam- 

 inations of water for the typhoid bacillus an attempt 

 was made 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 principles. Among them, one of the earliest 

 was that of Parietti (Parietti, 1890), which consists 

 in the addition of the water to a series of broth tubes 



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