BACTERIOLOGICAL STUDY OF WATER. 589 



subject it to some method of treatment that will aid in 

 separating the few specific pathogenic from the numer- 

 ous common saprophytic species. For this purpose 

 numerous methods have been devised. The most use- 

 ful of these aim to favor the rapid multiplication of 

 pathogenic forms that may be present and to suppress 

 or check the growth of the ordinary water saprophytes. 



Attention has been called to the fact that when ex- 

 posed to the body-temperature many of the ordinary 

 water-bacteria develop only slowly or not at all, while 

 imder similar circumstances the disease-producing spe- 

 cies develop most luxuriantly. Advantage has been 

 taken of this observation 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 oi 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 pages 

 454, 467) ; and by taking advantage of the effect of ele- 

 vated 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 



