296 



A MANUAL OF BACTERIOLOGY 



The above results represent the monthly means of 

 the number of microbes (colonies) obtained from 1 

 cc. of water by the ' fractionnement ' method. 



The quarterly means are given in the next 

 table : 



From Miquel's analyses the quarterly means of the 

 number of microbes contained in 1 cc. of sewer- 

 water (collected at Clichy and St. Ouen, Paris) are 

 as follows : 



Winter, 

 Spring, 

 Summer, 

 Autumn, 



14,780,000 



16,760,000 



9,638,000 



6,375,000 



It appears from the observations of Miquel that the 

 largest number of microbes found in river and sewer 

 waters is during the spring months. The self- 

 purification of rivers polluted with sewage has given 

 rise to a great deal of discussion ; but there is no 

 doubt that in some rivers the sewage is rapidly 

 oxidised by the oxygen dissolved in the water or 

 separated from plants. Professor von Pettenkofer 1 

 states that sewage may be permitted to flow into a 



1 Chemiker Zeitung, 1891. 



