598 A MANUAL OF BACTERIOLOGY 



for the B. typhosus, unless all tests are applied to them, 

 are the B. (fcecalis) alkaligenes and B. (aquatilis) sulcatus. 

 Both occur in the dejecta and in polluted water, and are 

 very like the B. typhosus in morphology, motility, staining, 

 and cultural reactions, but neither agglutinates with 

 typhoid serum. The B. alkaligenes sometimes produces 

 a brownish growth on potato, it renders litmus milk 

 alkaline and produces alkali, but no gas, in glucose, lactose, 

 dulcitol, mannitol, saccharose, and salicin. The B. sulcatus 

 hardly grows at 37 C. and is almost a strict ae'robe, little 

 growth occurring in the depth of a stab. Some varieties 

 of typical and of atypical B. coli agglutinate with typhoid 

 serum, so that a positive agglutination reaction does not 

 necessarily prove that an organism is B. typhosus. 



THE ISOLATION or THE CHOLERA BACILLUS FROM WATER. The 

 detection of Koch's comma bacillus (Vibrio cholerce) in water, as 

 in the case of the typhoid bacillus, is a matter of some difficulty, 

 as this organism is rapidly overgrown 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 vibrio 

 multiplies with great rapidity in alkaline saline peptone solution. 

 The suspected water is examined as follows : To 300-500 c.c. of 

 the water are added 1 per cent, each of pure peptone and of common 

 salt ; the mixture is made faintly alkaline with sodium carbonate, 

 distributed in a dozen small Erlenmeyer flasks having a layer not 

 more than an inch deep in each, the flasks are loosely capped with 

 caps of filter-paper, and incubated at 37 C. At intervals of ten, 

 fifteen and twenty hours respectively, hanging- drop and cover-glass 

 preparations are made from the top of the liquid, an which there 

 is often a surface film, and care must be taken not to disturb this ; 

 these are then examined microscopically for vibrios and spirilla. 

 At the same time agar (3 per cent.), or, better, blood alkali agar 

 (p. 446) plates are prepared and incubated at blood-heat. Any 

 colonies that appear which resemble the cholera spirillum are 

 examined microscopically ; if the organisms are comma-shaped, 

 they are at once subcultured into peptone water and other media. 

 The original peptone water cultures are tested for the indole reaction 

 with pure hydrochloric acid, withdrawing some of the contents of 



