EXAMINATION OF WATER 395 



treatment. This treatment affected the aerobic bacilli to 

 such a degree that it reduced them from over 3,000,000 

 per cubic centimetre in the untreated effluent to 160 per 

 1 c.c. in the treated effluent ; but when examining the 

 effluent on the above lines for the presence of anaerobic 

 spores, it was found that these latter, as also other spores, 

 had remained unaffected by the treatment. This Klein 

 considers is sufficient proof to show the importance of the 

 analysis embracing also anaerobic cultures ; the same 

 applies to the bacteriological analysis of water, in which 

 the detection of aerobic sewage organisms may be difficult 

 owing to their small number, but may nevertheless contain 

 the spores of some definite anaerobic sewage organisms. 



The Isolation of the T3rphoid Bacillus from Water. — There 

 is very great difficulty in isolating the B. typhosus from 

 water that has been very copiously contaminated with 

 specifically polluted sewage ; there is even greater difficulty 

 in detecting it when the specific pollution has been small in 

 amount. It is necessary to bear in mind that usually, 

 when drinking-water has suffered sewage-pollution, the 

 amount of the pollution is relatively very minute when 

 compared with the great bulk of the water-supply. The 

 contamination of water by sewage is, moreover, in the 

 majority of cases, of an intermittent nature. 



When such waters are examined, it is easy to miss the 

 colon bacillus, not to speak of the typhoid bacillus. 



In order to isolate the B. typhosus suspected to be present 

 in a sample of water, it is necessary to submit a large 

 volume of the water to examination. This object is attained 

 by concentrating the bacterial contents of the water by 

 passing 1,000 to 3,000 c.c. or more of the sample through 

 a small sterile Pasteur- Chamberland filter. By this treat- 

 ment all the bacteria in the water are retained on the outer 

 surface of the filter. The particulate matter thus retained 



