1920] 
CHAMBERS—BACTERIAL INHIBITION BY METABOLIC PRODUCTS 275 
Pa 7.3, 7.1, 7.6, 7.5, and 7.4. The relation between growth 
curves and P, curves, fig. 7, would indicate that Bacillus coli 
is more sensitive to alkali than to acid and that amounts of 
alkali or acid considerably less than the fatal dose become promi- 
nent factors in inhibiting growth. 
Supplementing the preceding table, table vri gives the results 
of growth of Bacillus coli in 1 per cent, 2.5 per cent, and 5 per 
cent dextrose media. A synthetic bouillon was used for these 
cultures consisting of .5 per cent asparagin, .5 per cent K,HPO,, 
and the dextrose as indicated. The growth and hydrogen ion 
concentration curves are plotted in fig. 8 on the same basis as 
the eurves in all the other figures. As might be expected, the 
action in general corresponded to that of Culture 2, fig. 1, which 
was grown in 1 per cent dextrose. Both the growth and P; 
eurves showed a small lag at the beginning in 2.5 per cent dex- 
trose and a greater one with some decrease in growth in 5 per 
cent dextrose. Following the initial lag, the cultures produced 
the usual growth, acid fermentation, and death. A slightly 
greater acid production occurred in the 5 per cent dextrose, 
for the hydrogen ion concentration went to P, 4.7. The data of 
tables vir and vir show that in cultures of Bacillus coli sufficient 
acid to kill the organisms was formed from 1 per cent or more 
of dextrose, while .15 to .3 per cent supplied only enough acid 
to inhibit the growth, and .1 per cent exerted a stimulative 
action. Thus the amount of dextrose present seems to regu- 
late the reaction, which is a strong factor in growth and inhi- 
bition. 
In connection with the reversion of reaction, the growth 
and inhibition of Bacillus aerogenes are of interest. One culture 
of plain bouillon and one culture of plain bouillon plus 1 per 
cent dextrose were inoculated with Bacillus aerogenes; the growth 
and hydrogen ion concentration changes are recorded in table 1x 
and fig. 9. Both the growth and hydrogen ion concentration 
were very similar to those of Bacillus coli from the time of inocu- 
lation up to 96 hours. As fig. 9 illustrates, at 96 hours the abrupt 
descent of the growth curve was checked at 7,600,000 bacteria 
per cc. The slight drop to 5,000,000 bacteria per cc. in the 
next 48 hours was followed by a second rise which culminated in 
a maximum of 1,017,000,000 bacteria per cc. at 696 hours. 
