The Bacteria in Natural Waters. 19 



EFFECT OF OXYGEN ON VIABILITY OF TYPHOID 



BACILLI IN STERILE TAP WATER. 



(WHIPPLE AND MAYER, 1506.) 



yVarious inorganic constituents of the medium un- 

 doubtedly exercise an important influence upon the life 

 of bacteria in water; and the mutual interaction of the 

 different substances present is a highly complex one. 

 Thus Winslow and Lochridge (1906) report that five parts 

 of dissociated hydrogen per million parts of tap water 

 (.005 normal HCl) is fatal to typhoid baciUi, while ten 

 times as much acid is required for sterilization when one 

 per cent of peptone is present to check the dissociation of 

 the hydrogen. 



' ' Although it is hard to estimate the exact importance of 

 each factor, the general phenomena of the self-purification 

 of streams are easy to comprehend. A small brook 

 immediately after the entrance of polluting material from 

 the surface of the ground contains many bacteria from a 

 diversity of sources. Gradually those organisms adapted 



