Isolation of the Colon Bacillus. 91 



rapid development of B. coli takes place in the first few 

 hours after dextrose solutions are inoculated with intes- 

 tinal material, and a nearly pure growth of colon bacilli 

 often results, while other bacteria multiply more slowly. 

 With highly polluted waters gas formation will probably 

 begin within twelve hours, but with fewer colon bacilli 

 present the duration must be increased. If the period 

 of incubation be too long continued, trouble in the subse- 

 quent steps of the isolation may be encountered because 

 of the overgrowth of B. coli by the sewage streptococci, 

 or other forms which check the growth of the colon bacilli 

 in the later stages of fermentation and finally kill them 

 out. 



As has already been stated, phenol has less inhibitory 

 action upon B. coli than upon normal water-bacteria, 

 and it was hoped that a broth containing this substance 

 might be employed for preliminary enrichment with ad- 

 vantage, its inhibitory power checking the overgrowing 

 forms, but not B. coli. This medium was used in place 

 of dextrose broth for many of the studies made in con- 

 nection with the Chicago drainage canal (Reynolds, 1902). 

 Phenol broth consists of ordinary broth to which o.i per 

 cent phenol is added, and the method of procedure is to 

 add i c.c. of the water to 10 c.c. of the sterilized phenol 

 broth and incubate at body temperature for twenty-four 

 hours. Litmus-lactose-agar plates are then made and 

 the examination of the red colonies carried out as described 

 for the dextrose-broth method. It has unfortunately 



