310 APPLIED • BACTERIOLOGY 



bacillus may have been annihilated by the common water 

 bacteria. 



Therefore, to say that a given water was safe because no 

 specific organism was demonstrable, and to ignore the 

 information that a chemical analysis might yield, would be 

 entirely illogical. 



The Isolation of the Cholera Bacillus from Water. — The 

 detection of Koch's comma bacillus (Spirillum cholerce 

 AsiaticcB) in water, as in the case of the typhoid bacillus, is 

 a matter of some difficulty, as this organism is rapidly over- 

 grown by the ordinary water bacteria. In the examination 

 of suspected water-supplies, the best method to employ for 

 the detection of this organism is to take advantage of the 

 fact first noted by Dunham, that the cholera spirillum 

 multiplies with great rapidity in alkaline saline peptone 

 solution. The suspected water is examined as follows : To 

 100 c.c. of the water are added 1 gramme each of pure peptone 

 and common salt ; the mixture is made faintly alkaline with 

 sodium carbonate, and then incubated at 37° C. At intervals 

 ■of ten, fifteen, and twenty hours respectively, cover-glass 

 preparations are prepared from the top of the liquid ; these 

 are then microscopically examined for spirilla. At the same 

 time agar plates are prepared, and incubated at blood-heat. 

 Any colonies that appear which resemble the cholera spiril- 

 lum are examined microscopically; if the organisms are 

 comma-shaped, they are at once subcultured into broth and 

 other media. The broth-tubes after incubation are tested 

 for the indol reaction, and if possible by animal inoculation. 



It is well known that many impure, especially sewage- 

 contaminated waters, contain spirilla and comma-shaped 

 bacteria, many of which strongly resemble the cholera 

 organism in many ways ; care must therefore be taken that 

 none of these are mistaken for the true cholera organism. 

 None of these spirilla forms, however, give the indol 



