EXAMINATION OF WATER 



305 



was then incubated at blood-heat and the water afterwards 

 plate-cultured. 



As pointed out by Holz, and confirmed by Dunbar, the 

 above authors use a percentage of phenol which altogether 

 prevents the growth of the B. typliosus. Dunbar states 

 that 0'12 per cent, of phenol greatly interferes with the 

 growth of the typhoid bacillus, while in the presence of 

 0"14 per cent, it will not develop at all. He further states 

 that in the presence of small quantities of phenol the colon 

 bacillus presents stronger resemblances to the typhoid 

 bacillus than usual. 



To ascertain if the resisting power of cultures of the 

 B. typliosus to phenol differed, we tried the following series 

 of experiments on different cultures of the organism, using 

 varying percentages of phenol, with the following results : 



Thus, it is seen that the resisting power of the B. typhosus 

 to phenol varies with different cultures. The sample marked 

 («), which was freshly isolated from the dejecta from a 

 typhoid case, had less resistiag power than other samples 

 which had been subcultured through many generations. 



Parietti proposed the use of broth containing both phenol 

 and hydrochloric acid to eliminate the common water 

 organisms. He takes advantage of the fact that the typhoid 

 and colon bacillus will grow in a slightly acid medium, 

 whereas the majority of other organisms will not. 



Parietti's method is as follows : The following solution is 

 prepared : Five grammes of phenol and 4 grammes of pure 



20 



