THE BACTERIOLOGICAL EXAMINATION OF SEWAGE 861 



To give some concrete notions with regard to the nature and number of 

 organisms found in water some figures may be abstracted from Dr. Houston's 

 reports. Taking the London Metropolitan water supply for the year ending 

 March 31st 1909 : 



1. Total number of organisms (Gelatin plates at 20-22 C. 3 days). 



2. " Typical " colon bacillus test. 



The bacteriological examination of sewage. 



[Houston's method of water examination is equally applicable to the 

 investigation of the nature and number of organisms present in sewage. In 

 this case, of course, the sewage must be diluted to a far greater extent than 

 is necessary in the case of water and it will be necessary to examine 0000,001, 

 0-000,000,1 and even 0-000,000,01 c.c. for the presence of colon bacilli.] 



