23 



Group B are quite differently distributed with respect to this average. In 

 large collection of data inspection is impracticable but the standard devi- 

 ation serves well in its place. The standard deviation in Group A is 

 0.07 while for Group B it is 0.25. The larger deviation in B denotes 

 that the individuals in the group wander farther away from the average than 

 do those in Group A. 



Acid Production from Glucose. Considering 156 strains, isplated 

 from various sources (including sheep, horse, cow, pig, man, and sewage), 

 the V. P. negative (coli section) gave an average of 1.82 percent normal 

 acid with an empirical mode at 1.9 percent while the V. P. positive (aero- 

 genes section) produced an average of 1.46 percent with a mode at 1.5 

 percent normal acid. Although the difference (0.36 0.04) is not 

 very large, it appears significant for rather striking differences in 

 acid formation between the V. P. positive and V. P. negative strains are 

 observed with many other test substances, as maltose, sucrose, glycerol, 

 and dulcitol. This observation is also in line with the work of Harden 

 and Walpole, already referred to that Bact. aerogenes produces less acid than 

 Bact. coli from glucose. 



TABLE IX. ACID PRODUCTION BY COLON GROUP FROM GLUCOSE AND 



SUCROSE. 



"Only fermenters included in calculations. 



Acid Production from Sucrose. Sucrose is not attacked by all 

 members of the colon group. It is practically always fermented, how- 

 ever, with acid and gas production by the aerogenes section and many of 

 the strains of the coli section. In the foregoing table are given the fre- 



