20 



Elements of Water Bacteriology. 



EXAMINATIONS OF THE ISAR AT PULLACH. 



(RAPP, 1903.) 

 (A) Carried out September 26, 1898, no rain having fallen for three weeks. 



(B) Carried out November 28, 1898, no rain having fallen for some time. 



to life in the earth or in the bodies of plants and animals 

 die out, and the forms for which water furnishes ideal 

 conditions survive and multiply. It is no single agent 

 which brings this about, but that complex of little-under- 

 stood conditions which we call the environment. If any 

 one thing is of prime importance it is probably the food- 

 supply, for only certain bacteria are able to multiply in 

 the presence of the small amount of organic matter present 

 in ordinary potable waters. As Jordan (Jordan, 1900) 

 has said: "In the causes connected with the insufficiency 

 or unsuitability of the food-supply is to be found, I believe, 

 the main reason for the bacterial self-purification of 

 streams." 



