1920] 
CHAMBERS— BACTERIAL INHIBITION BY METABOLIC PRODUCTS 269 
are given in table v. A more striking representation of the 
changes in the concentration of the hydrogen ions is shown 
in the curves in fig. 5. Growth in both cultures is practically 
parallel, with the dextrose culture reaching the highest point— 
885,000,000 per cc. at 234 hours. From a comparison of these 
growth curves with those of fig. 1, it is quite evident that neu- 
tralizing the acid or alkali prolongs the growth at a higher level. 
The P4 curve for the dextrose culture shows an abundant 
production of acid, going as high as P, 5.1 several times. Be- 
tween 72 and 96 hours, however, the formation changed to alkali, 
and N/5 HCl was added to neutralize. ‘Table v shows that 
37.8 cc. of N/1 NaOH were required to neutralize the acid 
from 1 per cent dextrose and that in the same time, 96 hours, 
19 ec. of N/5 HC1 were used in neutralizing the alkali in the 
plain bouillon, giving a ratio of 189 to 19, or approximately 
10 to 1. Theoretically, then, one-tenth of the dextrose, or .1 
per cent dextrose, would furnish just enough acid in 96 hours to 
neutralize the alkali formed in plain bouillon, and would hold 
at neutral the hydrogen ion concentration of a growing culture 
which was fermenting dextrose, if the dextrose were added in 
small amounts at frequent intervals. 
On this basis a culture was started in plain bouillon. The 
amounts of dextrose added, the growth, and the P, values are 
given in table vr and illustrated in fig. 6. By 72 hours the 
hydrogen ion concentration had demonstrated that the the- 
oretical amount, .025 per cent of dextrose every 24 hours, did 
not furnish sufficient acid to neutralize the alkali, so the amount 
of dextrose was increased and the intervals between additions 
shortened to meet the needs of the culture. The reaction, with 
each addition of sugar, depends on the acid fermentation of 
the sugar and a subsequent alkali formation, as illustrated by 
the P,, curves between 48 and 72 hours and between 96 and 108 
hours. This alkali formation was reversed by the addition of 
more sugar at the proper time. Although the theoretical cal- 
culation was upset by the increased growth, the Pa curve dem- 
onstrates that it was possible to hold the hydrogen ion con- 
centration within à very narrow zone around the neutral point. 
The growth was very rapid, reaching 1,550,000,000 bacteria per 
cc. at 48 hours, or 21% times as many bacteria as Culture 2, 
