CHAPTER II 



THE QUANTITATIVE BACTERIOLOGICAL EXAMINATION 

 OF WATER 



Relation of the Medium to the Number of Bacteria 

 Obtained. The customary methods for determining 

 the number of bacteria in water do not reveal the total 

 bacterial content, but only a very small fraction of it, 

 as becomes apparent when we consider the large num- 

 ber of organisms, m'trifying bacteria, strict anaerobes, 

 etc., which refuse to grow, or grow only very slowly in 

 ordinary culture media, and which, therefore, escape 

 detection. On the one hand, certain obligate parasites 

 cannot thrive in the absence of the rich fluids of the 

 animal body; on the other hand, the prototrophic 

 bacteria, adapted to the task of wrenching energ}- from 

 nitrites and ammonium compoimds are unable to develop 

 in the presence of so much organic matter. Winslow 

 (1905) in the examination of sewage and sewage effluents, 

 found 20-70 times as many bacteria by microscopic 

 enumeration as by the gelatin plate count. Certain 

 special media enable us to obtain much larger counts 

 than those yielded by the ordinary gelatin method. 

 The Nahrstoff Heyden agar, for example, has been 

 strongly advocated by Hesse (Hesse and Niedner, 

 1898) and other German bacteriologists upon this 



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