COLON-AEROGENES FORMS FROM NATURAL WATERS 63 



intermediate between the colon and aerogenes types, their posi- 

 tive uric acid reaction seems to mark them as without signifi- 

 cance as indicators of pollution. There is a tendency of strains 

 grouped under 9 and 10 to approach the maximum of fermenta- 

 tive power ascribed by Winslow and his co-workers to Bad. 

 aerogenes as the most primitive type of the entire colon-typhoid 

 group. 



Five uric acid negative strains are acid to methyl red and 

 Voges-Proskauer negative: the two lie strains ferment all car- 

 bohydrates, etc., tested except starch; 11a resembles Bact. co7n- 

 jnunior in that it is salicin and dulcitol negative; the two strains 

 marked lib approach Bact. coli. 



The strains lie and lOd were isolated from apparently unpol- 

 luted wells, respectively 1300 and 2000 feet deep. 



The remaining strains are spore bearers, excepting No. 17, 

 which lost most of its original characters under laboratory culti- 

 vation. They resemble the strains 4, 5a and 5b in their failure 

 to ferment salicin, dulcitol and adonitol. 



The relative value of the three criteria for discrunination of 

 high and low ratio groups with these strains appears from the 

 following considerations: 15 uric acid positive strains ferment 

 mannitol, maltose, glucose, lactose, sucrose, salicin, dulcitol 

 adonitol, and glycerol, or all save one of the last three and are 

 considered as probable Bact. aerogenes forms; 2 are methyl red 

 negative; 7 give the Voges-Proskauer reaction, and 1 is variable. 

 There are 13 discrepancies in the methyl red and uric acid tests, 

 and 7 or 8 in the uric acid and Voges-Proskauer tests. Two 

 uric acid positive strains which failed only in fermenting dulcitol 

 were not tested with salicin: 1 was acid to methyl red and was 

 Voges-Proskauer positive; 1 was negative in both reactions. 

 The uric acid test was confirmed by one of these reactions and 

 negatived by the other in each instance. 



Two strains (lib) fermented all the above listed sugars, etc., 

 save glycerol, but were uric acid negative, methyl red positive, 

 Voges-Proskauer negative in repeated tests. These are the only 

 instances which raise a question as to the validity of the Uric 

 acid reaction, which in all other cases cited appears preferable 

 in discriminating high ratio members in waters. 



