50 WATER 



Houston also carried out some experiments upon the com- 

 parative vitality of the typhoid bacillus in raw Thames river 

 water at different temperatures. He found that temperature 

 exerted a powerful influence, the bacillus living considerably 

 longer at low (32 42 F.) than at higher (50 gS'6 F.) tempera- 

 tures. 



It may be said, as a general result from the experimental 

 evidence, that typhoid bacilli do not live for long periods in 

 drinking water, their total elimination being a matter of only a 

 few weeks, while the vast majority are destroyed within a few 

 days. At the same time it is hardly justifiable to assume that 

 all typhoid bacilli gaining access to water will be eliminated 

 even within a month in all classes of water. Such a conclusion 

 is probably true as applied to the storage of raw river water, but 

 with local well water contaminated with the faeces of a typhoid 

 fever case or carrier the conditions particularly as regards the 

 nutritive condition of the water are considerably altered from 

 those made use of in the experimental work and deductions from 

 these experiments may not apply. It is quite possible that the 

 bacilli may persist for considerably longer periods. 



Wilson and Dickson 1 added a mixture of typhoid "carrier" 

 urine and faeces to 60 litres of water in an open reservoir and 

 recovered the typhoid bacillus after three weeks and two days. 



As regards the comparative vitality of B. typhosus and B. coli 

 in water, comparative results show clearly that the former is 

 the more delicate organism and dies out first. The proved 

 absence of the second organism may therefore be taken since 

 almost invariably contamination with B. typhosus is accompanied 

 by much heavier contamination with B. coli as evidence of the 

 absence of the typhoid bacillus. The only exception would be 

 when the contamination was by the urine of a typhoid case or 

 carrier containing only typhoid bacilli and no B. coli. 



Bacterial content of different classes of waters. 



Before the significance of the results of the bacteriological 

 examination of water samples can be properly appreciated 



1 Journ. Royal Sanitary Instit. 1911, vol. xxxu,.p. 472. 



