BACTERIA IN WATER 161 



forms pathogenic to man. The chief interest here, so far as 

 Europe is concerned, lies in the fact that typhoid fever is so 

 frequently water-borne, but cholera and certain other intestinal 

 diseases have a similar source. The search in waters for the 

 organisms concerned in these diseases is a matter of the greatest 

 difficulty, for each belongs to a group of organisms morpho- 

 logically similar, very widespread in nature, and many of which 

 have little or no pathogenic action. The biological characters 

 of these organisms will be given in the chapters devoted to 

 the diseases in question, but here it may be said that from 

 the public health standpoint the making of their being found 

 a criterion for the condemning of a water is impracticable. There 

 is no doubt that the typhoid and cholera bacteria can exist 

 for some time in water at least this has been found to be the 

 case when sterile water has been inoculated with these bacteria. 

 But to what extent the same is true when they are placed in 

 natural conditions, which involve their living in the presence 

 of other organisms, is unknown, for by no known method can 

 the presence of either be with certainty demonstrated in the 

 complex mixtures which occur in nature. With regard to 

 the typhoid bacillus, of late the tendency has been to seek for 

 the presence of indirect bacteriological evidence which might 

 point in the direction of the possibility of the presence of this 

 organism. The whole question turns on the possibility of 

 recognising bacteriologically the contamination of water with 

 < wage. Klein and Houston here insist on the fact that in 

 crude sewage the b. coli -or the members of the coli group are 

 practically never fewer than 100,000 per c.c., and therefore if 

 in a water this organism forms a considerable proportion of the 

 total number of organisms present, then there is great reason 

 for suspecting sewage pollution. In these circumstances, all 

 modern work tends to taking the presence of b. coli in a water 

 as the best indirect evidence of the possibility of disease 

 organisms of intestinal origin being likely to gain access to 

 that water. It must, however, be at once clearly recognised that 

 the presence of members of the coli group is only an indication, 

 and so far as the potability of any water is concerned, there 

 is no evidence that these organisms, however undesirable, are 

 under ordinary circumstances actually harmful to man. In all 

 inquiries there is the difficulty that at present no means exist 

 of differentiating between b. coli as derived from the human 

 inti-stine on the one hand, and from the intestine of animals 

 on the other. It is thus necessary in reporting upon a water to 

 havr had an opportunity of inspecting the locality. We have 

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