STUDY OF WATER. 421 



widespread epidemic outbreaks, and almost as often do 

 reliable bacteriologists fail to detect the bacillus that is 

 the cause of typhoid fever in these waters. 



The failure to find the organisms of typhoid fever in 

 water by the usual methods of analysis does not by 

 any means prove that they are not present or have not 

 been present. The means that are ordinarily employed in 

 the work admit of such a very small volume of water 

 being used in the test that we can readily understand how 

 these organisms might be present in moderate numbers 

 and yet none of them be included in the drop or two 

 of the water that are taken for study. The conditions 

 are not those of a solution, each drop of which contains 

 exactly as much of the dissolved material as do all 

 other drops of equal volume, but are rather those of a 

 suspension in each drop or volume of which the number 

 of suspended particles are liable to the greatest degree 

 of variation. Furthermore, there are other reasons 

 that would, a prion, preclude our expecting to find 

 the typhoid bacilli in water in M'hich we may have 

 reason to believe they had been deposited, viz., atten- 

 tion is not usually directed to the water until the 

 presence of the disease has become conspicuous, usually 

 in from three to four weeks after the time when the 

 pollution probably occurred. Three or four weeks is 

 ordinarily sufficient time for the delicate, non-resistant 

 bacillus of typhoid fever to succumb to the unfavorable 

 conditions under which it finds itself in water. By 

 unfavorable conditions is meant the absence of suitable 

 nutrition ; unfavorable temperature ; probably the an- 

 tagonistic influence of more hardy saprophytic bacteria, 

 particularly the so-called " water bacteria," and of more 

 highly organized water plants ; the effect of mechanical 



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