THE BACTERIA IN NATURAL WATERS 15 



adds: " It is noteworthy that all the instances recorded 

 in the literature where a marked bacterial purification 

 has been observed are precisely those where the con- 

 ditions have been most favorable for sedimentation." 



Little is known as to the share of other organisms in 

 hastening the decrease of bacteria in stored water. 

 Doubtless predatory Protozoa play some part in the 

 process. Huntemiiller (1905) after infecting water 

 containing flagellate Protozoa with t}'phoid bacilli, 

 found the Protozoa crowded with bacteria; and he 

 observed under the microscope the actual ingestion 

 of the living and motile bacilli. Korschun (1907) and 

 others have obtained similar results and consider the 

 activity of Protozoa to be an important factor in self- 

 purification. Fehrs (1906) found that t3/'phoid bacilli 

 would live for 7 days in unsterilized Goltingen tap water, 

 for 46 days in the same water sterilized, and for 13 

 days in water inoculated with a culture of flagellate 

 Protozoa after sterilization. Water bacteria were of 

 course added with the Protozoa. Stokvis and Swel- 

 lengrebel (191 1) have shown that ciliated infusoria 

 may also consume considerable quantities of bacteria 

 under favorable conditions as to oxygen and temperature, 

 and Horhammer (191 1) reports that certain Crustacea 

 such as Cyclops may devour considerable quantities 

 of typhoid bacilli when present in masses from cultures^ 

 stained with methylene blue, and suspended in water. 



Certain bacteriologists have held that the toxic waste 

 products of the bacteria themselves may render water 

 unfit for their own development. Horrocks (Horrocks, 

 1901), Garre (Garre, 1887), Zagari (Zagari, 1887) and 



