BACTERIA IN WATER 55 



Prausnitz has shown that water differs, as would be ex- 

 pected, according to the locality in the stream at which 

 examination is made. His investigations were made from 

 the river Isar before and after it receives the drainage of 



Munich: 



No. of Colonies 

 per cc. 



Above Munich 531 



Near entrance of principal sewer 227,369 



13 kilometres from Munich 9,m 



22 " " " 4,796 



33 " " 2,378 



Professor Percy Frankland also points out how the river 

 Dee affords another example, even more perfect, of pollution 

 and restoration repeated several times until the river be- 

 comes almost bacterially pure. 



We cannot here enter more fully into the many conditions 

 of a water which affect its bacterial content than to say that 

 it varies considerably with its source, at different seasons, 

 and under different climatic conditions. An enormous in- 

 crease will occur if the sediment is disturbed, and conversely 

 sedimentation and subsidence during storage will greatly 

 diminish the numbers of bacteria. Sand filtration, plus a 

 " nitrifying layer," will remove more than 90 per cent, of the 

 bacteria. Sea- water contains comparatively few bacteria, 

 and the deeper the water and the farther it is from shore so 

 much less will be the bacterial pollution. 



THE CHIEF DISEASE ORGANISMS FOUND IN WATER 



We will now consider several of the more important dis- 

 ease-producing bacteria found in water. 



Bacillus Typhosus (Eberth-Gaffky). In 1 880-81 Eberth 

 announced the discovery of this bacillus in cases of clinical 

 enteric fever. In 1884 it was first cultivated outside the 

 body by Gaffky. Since then other organisms have been held 



