Report on the Bacteriology of Water. 405 



direct experiment, i.e., . by purposely introducing the bacillus into 

 water, and in this manner the conditions which are favourable and 

 unfavourable to the vitality in water of the typhoid bacillus can, of 

 course, be much more readily ascertained than by the study of 

 such chance cases as those already enumerated above, in which the 

 bacilli had, in the natural course of events, gained access to water. 



I have below expressed in a tabular form, the principal results of 

 the numerous investigators who have already availed themselves of 

 this method of experimenting on the behaviour of the typhoid bacillus 

 iii water. 



From this table it will be seen that different observers ascribe very 

 different degrees of vitality to ' the typhoid bacillus in water, nor is 

 this to be wondered at when it is remembered that the typhoid 

 bacilli introduced into the waters may have been possessed of very 

 different degrees of initial vitality according to their age and previous 

 history ; whilst, secondly, the waters experimented with were, of 

 course, not the same ; thirdly, the amount of food-material introduced 

 into the water along with the bacilli must have been subject to the 

 very greatest variations, and again the temperatures and other condi- 

 tions under which the infected waters were preserved were equally 

 variable. 



Thus, taking the experiments made with distilled water, in which, 

 therefore, there is the most chance of the water having been of 

 uniform quality, Braem found the introduced typhoid bacilli still 

 alive after 188 days, whilst the longest duration, of vitality in this 

 medium observed by Hochstetter was five days, Meade Bolton, 

 Slater, Straus and Dubarry, and Wolffhiigel and Riedel giving 

 periods intermediate between these two wide extremes. These dis- 

 crepancies in the case of distilled water are doubtless to be accounted 

 for partly by the difference in initial vitality possessed by the different 

 typhoid bacilli employed and partly by the difference in the amount 

 of culture-material imported into the distilled water along with the 

 bacilli themselves, whilst the actual numbers in which the bacilli 

 were introduced may also greatly influence the degree of longevity 

 observed. 



This wide divergence in the results obtained by previous observers 

 would alone call for a reinvestigation of this subject with a view to 

 ascertaining the longevity of the typhoid bacillus in definite types of 

 British potable water, and taking more into consideration the exact 

 chemical composition of the waters experimented with. 



There is, however, another point arising out of the results arrived 

 at by previous investigators which still more urgently demands re- 

 investigation with a view to its confirmation, qualification, or direct 

 contradiction, and this is the relatively far greater longevity of the 

 typhoid bacillus in sterilised than in unsterilised potable water, 



