104- BACTERIOLOGICAL EXAMINATION OF WATER. 



the remaining three failed in one or more of the reactions 

 considered characteristic of the typical B. coli. The statement 

 that B. coli exists abundantly in all waters and soils appears to 

 be based on a very elastic interpretation of the characteristics of 

 B. coli. That this is a probable explanation is rendered manifest 

 by the experiments just published by Weissenfeld. This observer 

 examined water from thirty good wells, and found B. coli in 

 1 c.c. of seven of the specimens but only in one litre of the 

 remaining samples. He, however, found B. coli in 1 c.c. 

 of the water from twenty-four out of twenty-six bad 

 wells. Weissenfeld gives the cultural characteristics of 

 B. coli as follows : Superficial colonies on gelatine like 

 a vine-leaf; produces gas in sugar-agar-stab ; more or less 

 motile ; often not motile ; not stained by Gram's method. He 

 considers the souring of milk and the production of indol to be 

 of no value as distinguishing characteristics. These cultural 

 reactions, in my opinion, are not sufficient to differentiate the 

 B. coli from a large class of coliform organisms which are found 

 in very many waters from perfectly unpolluted sources. Whether 

 these coliform organisms are derived from a typical B. coli, 

 which by prolonged immersion in pure water has lost the power 

 of souring milk and producing indol, it is impossible to say ; 

 but the important point is that these organisms are found alone 

 and without any admixture of the typical forms of B. coli in 

 pure waters. Now when pollution of a water is produced by 

 sewage, probably at least half the cultures of B. coli present 

 will show all the typical characteristics of this organism, the 

 remaining cultures presenting the varying reactions of the 

 atypical members of this group. In my experience pollution 

 by sewage is never characterised by the presence solely of the 

 variety, which only produces gas in sugar media. The other 

 typical members of the group must also be present to warrant 

 the suspicion of sewage contamination. 



The statement that B. coli multiplies outside the animal 

 body is only true under certain very favourable conditions. 

 There is every reason to believe that when the physical conditions 

 are unfavourable its growth is inhibited, and it soon loses its 

 vitality and dies out. Also it is not justifiable to assume that the 

 excreta of animals are harmless to man, and in any case a water 



