168 MICKO-ORGANISMS IN WATER 



Seine in four drains, and the following table gives the 



results obtained : — 



Average Bacterial contents of effluent from Gennevilliers 

 (Miquel, 1891) 



Miquel states that at the point where these drains 

 communicate with the Seine the number of bacteria in 

 the river rises to above 200,000 per c.c. 



In connection with these results, however, we would 

 point out that, in conducting investigations (whether 

 bacteriological or chemical) on the efficiency of sewage 

 purification on the large scale, it is necessary that the 

 greatest caution should be exercised, otherwise the 

 most fallacious results may be arrived at. Thus the 

 composition of the raw sewage is continually varying, 

 and is utterly different at different times of the day ; 

 it is, therefore, very difficult, and in some cases quite 

 impossible, to institute comparisons between samples 

 of raw sewage and effluent, whilst the difficulty is fre- 

 quentlj'' further enhanced, especially in " the case of 

 sewage-works where land is employed, by the accession 

 during purification of more or less spring-water to the 

 sewage under treatment. It has long been customary 

 in the chemical investigation of sewage -purification to 

 look upon the chlorine as a rough indication of whether 

 the raw sewage and effluent are comparable, and there 

 can be no doubt that no reliance whatsoever should be 

 placed on results in which the chlorine in the effluent 

 differs materially from that in the raw sewage. The ex- 

 periments of the Massachusetts Board of Health, referred 

 to above, clearly indicate the enormous variation in the 



