590 sactehiology. 



importance in influencing our judgment upon the fitness 

 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 an Fermenta- 

 tion-tube) containing bouillon to which 2 per cent, of 

 glucose has been added, and keeping them at the tempera- 

 ture 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 fer- 

 mentation-characteristics of most of these organisms is 

 evidenced by the accumulation of gas in the closed end 

 of the tube. From these tubes the growing bacteria 

 can then be easily isolated by the plate method, and 

 intestinal bacteria will not infrequently be found 

 present. 



For the isolation of the typhoid bacillus, especially from 

 water, a host of other methods have been devised. Some 

 of these aim, through the addition of special chemical 

 reagents to the media, to retard the development of 

 ordinary saprophytes without interrupting the gi'owth 

 of the colon and the typhoid bacillus. Most of these 

 methods have proved disappointing. One of them, that 

 of Parietti, still finds favor in the hands of some. It 

 consists in adding to the culture-media to be used in 

 the test varying amounts of the following mixture : 



Phenol . . . 5 grammes. 



Hydrochloric acid . ... . 4 " 



Distilled water . . . 100 c.c. 



Of this solution 0.1, 0.2, and 0.3 c.c. are added re- 

 spectively to each of three tubes containing 10 c.c. of 

 nutritive bouillon. Several such sets of tubes are to be 



