THE MICROBES OF WATER 289 



which enter the system through the medium of 

 water. In view of these facts the bacteriological 

 analysis of water is a subject of great importance ; 

 but the primary object in such analyses is not the 

 search for pathogenic microbes. Such an investi- 

 gation is generally fraught with insuperable diffi- 

 culties, and, for sanitary purposes, is practically 

 worthless. ' It is obvious that, even if the typhoid 

 bacillus, or any other pathogenic microbe could be 

 detected with unerring certainty in any water in 

 which it was present, a search for this bacillus in 

 the ordinary course of water examination would 

 still have only a very subsidiary interest. Waters 

 are surely not only to be condemned for drinking 

 purposes when they contain the germs of zymotic 

 disease at the time of analysis, but in all cases 

 when they are subject to contaminations which 

 may at any time contain such germs. Sewage- 

 contaminated waters must on this account be in- 

 variably proscribed, quite irrespectively of whether 

 the sewage is, at the time that the water is sub- 

 mitted to examination, derived from healthy or 

 from diseased persons. . . . The real value of these 

 bacteriological investigations, if judiciously applied, 

 consists in their power of furnishing us with in- 

 formation as to the probable fate of dangerous 

 organisms, should they gain access to drinking 

 water. It is by their means that we have learnt 

 that many such organisms can preserve their 

 vitality, nay, in some cases can actually undergo 

 multiplication in ordinary drinking water ; that 

 they are destroyed by maintaining the water at the 



