CHAPTER XL 

 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 ammonias, nitrates, 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 stand point be considered as positive 

 evidence of human fecal contamination. Theoretically, the possibility 

 of organisms being present corresponding culturally to B. coli and de- 

 rived from cereals is to be considered. Also the faeces of animals con- 

 tain 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. enteritidis sporogenes as of value as indicators as well 

 as the B. coli the presence of sewage streptococci indicating very 

 recent sewage contamination and that of the B. enteritidis sporogenes, 

 in the absence of streptococci and colon bacilli, as evidence of sew r age 

 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. 



In collecting samples of water for bacteriological examination, the 

 following points should be considered: 



i. The bottles, which should have a capacity of from 25 to 100 c.c,, 



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