Q UALITA TIVE EX AM IN A TION OF WA TER 1 1 5 



{c) B. typhosus may be examined for by adopting exactly the 

 same methods as for B. coli. Its detection in, and isolation from, 

 water supplies is so difficult as to be well-nigh impossible. The 

 condition of a water is, however, ascertainable short of an absolute 

 test for B. typ/iosus, valuable though that would be. 



{d) Sewage organisms and the organisms indicative of surface 

 pollution should also be examined for. If they be present in the 

 water, it may be taken as proved that such water has been recently 

 polluted, and should be condemned. Crude sewage generally 

 contains in i c.c : {a) i-io million bacteria; {b) 100,000 B. coli (or 

 closely allied forms) ; {c) 100 spores of B. enteritidis sporogenes ; and 

 {d) 1000 streptococci (Houston). Further, so minute a quantity 

 as ximr of ^ c.c. of crude sewage is usually sufficient to produce 

 " gas " in a gelatine " shake " culture in twenty-four hours at 

 20' C, and the inoculation of animals with crude sewage always 

 leads to a local reaction and not uncommonly results in death. 

 These three organisms, B. coli, B. enteritidis sporogenes, and 

 streptococci have been termed the " microbes of indication," These 

 bacteria are wholly, or relatively, absent from pure water, and 

 their presence, at all events in considerable numbers, must be 

 taken as indicating recent animal pollution} B. coli is a most accu- 

 rate measure of intestinal pollution, and far greater information as 

 regards the sewage pollution of water can be gathered by its 

 estimation, than by simply counting the total number of organisms 

 present in water. It is an intestinal parasite and tends to perish 

 in other media,"^ When it is present in a small stream, contamina- 

 tion from houses can generally be traced.^ 



^ Second Report of Royal Commission on Sewage Disposal^ 1902, pp. 26 and 



27. 



- Ibid., p. 99. 3 7^-^^ p jog. 



