H 



ELEMENTS OF WATER BACTERIOLOGY. 



Examinations op 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. 



brook immediately after the entrance of polluting mate- 

 rial from the surface of the ground contains a large num- 

 ber of bacteria from a diversity of sources. Gradually 

 those organisms adapted to life in the earth or in the 

 bodLs 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 

 ibout, but that complex of little-understood 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 po- 

 table waters. As Jordan (Jordan, 1900) has said: "In 

 the causes connected with the insufficiency or unsuitability 



