CHAPTER XI 

 BACTERIOLOGY OF WATER, AIR, MILK, ETC. 



BACTERIOLOGICAL EXAMINATION OF WATER 



WHILE in a chemical examination as to the character of a water 

 there are certain relations between the free and albuminoid ammonias, 

 nitrates, nitrites, chlorides, etc., which indicate the probable animal as 

 against vegetable nature of the organic matter present, yet it is a more 

 or less presumptive evidence. In a bacteriological examination of 

 water the finding of the colon bacillus may from a practical standpoint 

 be considered as positive evidence of human faecal contamination. 

 Theoretically, the possibility of organisms being present corresponding 

 culturally to B. coli and derived from cereals is to be considered. Also 

 the faeces of animals contain an organism which cannot be differentiated 

 from the colon bacillus. 



In detecting sewage contamination in water to which varying amounts of sewage 

 had been added, it was found that the bacterial tests were from 10 to 100 times 

 more delicate than the chemical ones. 



As showing sewage contamination of water, the presence of the B. coli has been 

 generally accepted as the most satisfactory indication. The English authorities 

 consider sewage streptococci and the spore-bearing B. enter itidis sporo genes as of 

 value as indicators as well as the B. coli the presence of sewage streptococci indicat- 

 ing very recent sewage contamination and that of the B. enteritidis spcro genes, in the 

 absence of streptococci and colon bacilli, as evidence of sewage contamination at some 

 period more or less remote. 



In the United States the colon bacillus alone is considered the indi- 

 cator of sewage contamination, and all tests, presumptive or positive, 

 are based on the presence of this organism. 



It is not the finding of the colon bacillus but rather the question of 

 its relative abundance that is involved in a water analysis. Thus the 

 finding of one colon bacillus in 50 c.c. of water would not have weight as 

 showing contamination, but the presence rather constantly of the colon 

 bacillus in i c.c. or less makes contamination of a water supply probable. 



In collecting samples of water for bacteriological examination, the following points 

 should be considered: 



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