BACTERIOLOGICAL STUDY OF WATER. 619 



water, or with the results of simultaneous analyses of 

 a number of samples from other sources of supply of 

 the locality. 



The aid of the bacteriologist is frequently sought in 

 connection with investigations of waters that are sup- 

 posed to be concerned in the production of disease, par- 

 ticularly typhoid fever, either in isolated cases or in 

 widespread epidemic outbreaks, and in these cases both 

 the bacteriologist 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 sus- 

 pended 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 



