614 APPLICATION OF METHODS OF BACTERIOLOGY 



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 sapro- 

 phytes without interrupting the growth 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 grams 



Hydrochloric acid 4 grams 



Distilled water 100 c.c. ^ 



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

 to each of three tubes containing 10 c.c. of nutritive bouillon. 

 Several such sets of tubes are to be made. To each are 

 then added from 1 to 3 c.c. of the water, and they are placed 

 in the incubator at body-temperature. It is said that 

 whatever development occurs consists only of the typhoid 

 or colon bacillus, or both, if they were present in the original 

 sample. They may then be isolated and separated by the 

 usual plate method, or, better still, through the application 

 of the methods of v. Drigalski and Conradi, of Ficker, or 

 of Hoffmann and Ficker, or several of these methods in 

 conjunction, detailed in the chapter on bacillus typhosus. 

 Personally we have not had much success with the Parietti 

 method. The typhoid bacillus has been isolated from water 

 by passing very large quantities of water through an ordinary 



