[Vor. 7 
252 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
but only a very little on the effect on growth of changes in hy- 
drogen ion concentration during growth. Clark (15) deter- 
mined the final Py of 16 cultures of Bacillus coli in 1 per cent 
dextrose medium as Py 4.67-5.16, and Clark and Lubs (15) 
in constructing their media for differentiating the members of 
the colon-aerogenes group showed that a reversion of reaction 
toward the alkaline may take place, depending on the dextrose, 
but they did not show the relationship between reversion of 
reaction and growth. Itano (16) reported that with Bacillus 
subtilis, Streptococcus erysipelatus, and Streptococcus lacticus in 
plain broth, acid was formed in alkaline media and alkali in 
the acid media, thus bringing the Py to a certain definite hy- 
drogen ion concentration. Fred and Loomis (17) showed a 
wide range of reaction for Bacillus radicicola, obtaining good 
growth between Py 3.9 and 11.1. They also demonstrated that 
the hydrogen ion concentration approaches the neutral point 
during growth. Shohl and Janney (17) found that P, 4.6- 
5.0 was inhibitory for Bacillus coli in urine. Ayers, Johnson, 
and Davis (18) added streptococci to the list of organisms whose 
final Py was demonstrated. They separated the pathogenic 
from the non-pathogenic forms on the basis of limiting hydrogen 
ion concentration, the former reaching Py 5.4-6.0 and the latter 
Py 4.6-4.7. 
The work of Ayers and Rupp (18) on simultaneous acid and 
alkali fermentations showed some interesting Py curves. They 
found in a .5 per cent dextrose medium that Bacillus coli pro- 
duced acid to Py 4.8 but that Bacillus aerogenes produced less 
initial acid and the reaction reverted to Py 6.5. From quan- 
titative determinations of dextrose and of formic, acetic, lactic, 
and succinic acids, they explained the reversion of Bacillus 
aerogenes as a fermentation of the organic acids, mostly formic 
and acetic, to carbonates. With the alkali-forming milk bac- 
teria, they showed alkaline fermentation of citrate, acid fer- 
mentation of dextrose, and a practically neutral reaction from 
the simultaneous fermentation of the citrate and dextrose. 
Gillespie (18) found Actinomyces chromogenus gave a poor 
growth at Py 4.8-5.2 and decreased the hydrogen ion concen- 
tration of the media during growth. Wyeth ('18) showed with 
Bacillus coli in glucose bouillon that the final P, varied with 
