BACTERIOLOGICAL STUDY OF WATER 613 



bacteria develop only slowly or not at all, while under 

 similar circumstances the disease-producing species develop 

 most luxuriantly. Advantage has been taken of this obser- 

 vation in devising methods for this particular work, of 

 which some of the following will prove serviceable: 



Collect in a sterilized flask a sample of about 100 c.c. 

 of the water to be tested, and add to this about 25 c.c. of 

 sterilized bouillon of four times the usual strength. This is 

 then placed in the incubator at 37° to 38° C, for thirty-six 

 to forty-eight hours, after which plates are to be made from 

 it in the usual way; the results will often be a pure culture 

 of some single organism, either one of the intestinal variety 

 or a closely allied species. By a method analogous to the 

 latter the spirillum of Asiatic cholera has been isolated from 

 water (see article on that organism) ; and by taking advan- 

 tage of the effect of elevated temperature upon the bacteria 

 of water Vaughan has succeeded in isolating from suspicious 

 waters a group of organisms very closely allied to the bacillus 

 of typhoid fever. 



Theobald Smith has suggested a method by which it is 

 easily possible to isolate, from waters in which they are 

 present, certain organisms that are of the utmost impor- 

 tance in influencing our judgment upon the fltness of the 

 water for domestic use. By the addition of small quantities 

 — one, two, or three drops — of the suspicious water to 

 fermentation-tubes (see article on Fermentation-tube) con- 

 taining bouillon to which 2 per cent, of glucose has been 

 added, and keeping them at the temperature of the body 

 (37° to 38° C), the growth of intestinal bacteria that may 

 be present in the water is favored, while that of the water- 

 organisms is not; in consequence, after from thirty-six to 

 forty-eight hours the fermentation-characteristics of most 



