ISOLATION OF SPECIFIC PATHOGENES 79 



isms of the B. subtilis group must be eliminated by- 

 microscopic examination, using the Gram stain. 



Preliminary Enrichment. In most cases plate isola- 

 tion is preceded by some sort of enrichment process 

 designed to favor the t>'phoid bacilli at the expense 

 of the members of the B. coli group. The original 

 use of carbol broth has been already discussed. In 

 Europe caffein media have been used for this purpose 

 and in the United States bile media have been strongly 

 recommended. 



The important fact that cafifein has an inhibitory 

 action on colon bacilli, announced by Roth (Roth, 

 1903) has given rise to much investigation, and offers 

 one of the most promising methods for the isolation 

 of the typhoid bacillus from water. Hoffman and 

 Ficker (Hoffman and Ficker, 1904) developed methods 

 for the isolation of B. typhi from faeces and from infected 

 water by its use in connection with nutrose and crystal 

 violet. For the isolation from infected water solutions 

 were prepared as follows : 



1. Ten grams of nutrose dissolved in 80 c.c. of steril- 

 ized distilled water. 



2. Five grams caffein, in 20 c.c. sterilized distilled 

 water. 



3. One-tenth gram of crystal violet in 100 c.c. water. 

 Solutions I and 2 were mixed by shaking together in a 

 flask, and the mixture poured into a flask containing 

 900 cubic centimeters of the water to be tested; 10 

 c.c. of solution 3 were gradually added, and the whole 

 thoroughly mixed by shaking and then incubated at 



