THE COLON GROUP OF BACILLI 119 



tests with 10 c.c. Again, in another series of samples 

 examined, of those which gave positive tests in smaller 

 portions 5.3 per cent were negative in 10 c.c, 4.7 per 

 cent in 100 c.c, and 7.7 per cent in 500 c.c. 



Fromme (19 10) has made an interesting study of 

 this point and reports that of 59 samples of water of 

 good quality which showed B. coli in small portions 

 25 per cent gave negative results in larger portions; 

 while of 654 samples of polluted waters 33 per cent 

 gave negative results in large portions and positive 

 results in smaller ones. These results are of value as 

 indicating the greater liability to loss by overgrowth 

 in polluted waters; but the absolute figures are much 

 higher than workers in this country obtain when the 

 enrichment cultures are carefully watched and plat- 

 ings made from them at an early period. 



The Use of Phenol Broth as an Enrichment Medium 

 to Check Overgrowths. 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 advantage, 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 connection with the Chicago 

 drainage canal (Reynolds, 1902). Phenol broth con- 

 sists 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 24 hours. Litmus- 

 lactose-agar plates are then made and the examination 



