442 BACTERIOLOGY. 



supposed to be concerned in the production of disease, 

 particularly typhoid fever, either in isolated cases or in 

 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 suspen- 

 sion 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 priori, preclude our expecting to find the 

 typhoid bacilli in water in which we may have reason 

 to believe they had been deposited, viz., attention 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 condi- 

 tions is meant the absence of suitable nutrition ; unfavor- 

 able temperature ; probably the antagonistic influence of 

 more hardy saprophytic bacteria, particularly the so- 



