304 MICRO-ORGANISMS IN WATER 



bacilli were nearly overwhelmed by them, the latter, 

 however, with larger additions of the salt were ren- 

 dered more capable of holding their own in compe- 

 tition with the water microbes. Sodium sulphide acts 

 prejudicially, as might be anticipated, on both the 

 water forms and the cholera bacilli, but the vitality of 

 the latter is most distinctly increased by the addition of 

 sodium chloride to the sodium sulphide ; on the other 

 hand the water bacteria are not favourably influenced 

 by this addition. 



Experiments were also made on the effect of adding 

 sodium chloride in conjunction with sodium carbonate 

 to this unsterile well-water, and it was found that 

 whilst a large and rapid increase took place in the 

 water bacteria, the cholera organisms, after holding 

 out a few days, disappeared entirely on the fourth 

 day ; on the other hand, when sodium chloride, sodium 

 carbonate, and sodium sulphide were added together, 

 the cholera bacilli multiplied extensively side by side 

 with the water microbes, and even after seven days the 

 former were demonstrable, although only two colonies 

 were found on the plate. 



Investigations at a lower temperature (12^ 16 C.) 

 were also made with unsterile water with various addi- 

 tions of salts, and it was found that in only two in- 

 stances could the cholera bacilli be detected after nine 

 days, and then only in those waters to which sodium 

 chloride, disodium phosphate, and sodium sulphide had 

 been added together. 



Trenkmann states that in all his investigations with 

 this unsterile water he found that an addition of sodium 

 chloride and sodium sulphide caused a rapid disap- 

 pearance of the majority of the different kinds of water 

 bacteria present, sometimes only one variety remaining 

 in competition with the cholera organism ; such sur- 



