640 APPLICATION OF METHODS OF BACTERIOLOGY 



nection with investigations of waters that are supposed to 

 be concerned in the production of disease, particularly 

 typhoid fever, either in isolated cases or in widespread 

 epidemic outbreaks, and in these cases both the bacteriolo- 

 gist and the person employing his services are cautioned 

 against being too sanguine of positive results, for in the 

 vast majority of instances reliable bacteriologists fail to 

 detect in these waters the bacillus that is the cause of 

 typhoid fever. 



Failure to find the organism of typhoid fever in water by 

 the usual methods of analysis does not by any means prove 

 that it is not present or has not been present. The means 

 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 typhoid bacilli might be present in moderate 

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

 water 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 every drop or volume 

 of which the number of suspended particles is 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, because attention is 

 not usually directed to the water until the disease has become 

 conspicuous, usually in from two to four weeks after the 

 pollution probably occurred. These intervals of time are 

 ordinarily sufficient for the delicate, non-resistant bacillus 

 of typhoid fever to succumb to the unfavorable conditions 

 under which it finds itself in water. By unfavorable con- 

 ditions are meant the absence of suitable nutrition; un- 



