PATHOGENIC BACTERIA IN DIFFERENT WATERS 307 



specific gravity of the latter than to the absence of 

 organic food-materials. 



In ordinary potable waters, when sterile, the cholera 

 spirilla retain their vitality for periods of time varying 

 from a few days to several months. 



In these sterile potable waters, the cholera bacilli 

 do not appear to undergo any extensive multiplication, 

 but a curious phenomenon has been observed in this 

 connection both by Wolffhtigel and Eiedel and by our- 

 selves, for on infecting such waters with cholera spirilla 

 we found that their numbers, as revealed by plate- 

 cultivation, underwent rapid reduction during the first 

 few days, which decline was subsequently followed by 

 a slight but appreciable increase, soon followed again 

 by a subsequent diminution. The probable explana- 

 tion of this would appear to be that a number of the 

 spirilla soon perish on being introduced into the water, 

 and that those hardier forms which survive then 

 undergo slight multiplication, possibly at the expense 

 of the food-materials set at liberty by their fallen com- 

 rades ; whilst it may also be due to the spirilla adapting 

 themselves, to a certain extent, to the aqueous medium, 

 for Wolffhugel and Eiedel found that on transferring 

 these cholera spirilla which had undergone this slight 

 multiplication to a fresh quantity of water, they con- 

 tinued to multiply appreciably in this also ; the results 

 were, however, not so uniform as to admit of this 

 hypothesis being accepted without further investigation 

 which the importance of the subject certainly demands. 



On the other hand, in sterile sewage, the extensive 

 multiplication of the cholera bacilli admits of no doubt 

 whatever, for in this material we found the organism 

 present in large numbers, even after eleven months, 

 enormous multiplication having taken place in the 

 interval. 



