1920] 
CHAMBERS—BACTERIAL INHIBITION BY METABOLIC PRODUCTS 283 
It appears improbable that Bacillus coli, grown under the 
conditions of the experiments reported, produces any “auto- 
toxin" or special inhibitory substance such as Eijkmann and 
others claimed. "The results given in tables 11 and 111 indicate 
that the slight inhibition increasing with the age of the culture 
is probably associated with a diminution in nutrients. No 
thermolabile product could be detected which would inhibit 
growth if the hydrogen ion concentration were corrected. It is 
difficult to reconcile the production of an enzymatie inhibiting 
substance with such growth as appears in figs. 1 and 6, especially 
as death did not occur in these cultures. In plain bouillon, 
fig. 1, the culture was viable after 75 days; and in dextrose 
Pauillon, fig. 6, with the hydrogen ion factor controlled, growth 
attained 3,750,000,000 bacteria per cc. in 7 days, and there 
were still present over 2,000,000,000 bacteria per cc. after 840 
hours. In addition there was no indication in the cultures in 
which death occurred that death could be attributed to an 
“autotoxin.” 
There is a direct relation between hydrogen ion concentration 
and inhibition. If the acid is formed from the fermentation of 
dextrose, with Bacillus coli, fig. 7 and table vri, there is no indi- 
cation of acid inhibition at Py 5.9 if maintained for only a short 
time. Some inhibition is apparent at Py 5.5 which increases 
with the time that the culture is exposed to this Py. There 
is à marked inhibition from an exposure of 72 hours to Py 5.1, 
fig. 7, but it is insufficient to cause death. Fig. 4, however, 
shows that a prolonged hydrogen ion concentration of Py 5.1 
is lethal, and in every case throughout the experimental work 
a Py of 4.9, when produced by acid fermentation of dextrose, 
proves fatal, figs. 1, 2, 3, 4, and 8. 
To illustrate the relationship between hydrogen ion concen- 
tration and growth, four curves from figs. 1, 6, and 7 are as- 
sembled in fig. 11. "The highest growth curve, No. 2, is attained 
in the culture in which the Py remains practically neutral; the 
Py of 5.1, No. 3, produces an intermediate growth; and the slight 
eno in hydrogen ion concentration pen Py 5.1, No. 3, 
and 4.9, No. 4, is fatal. 
The OH ions also prove to be inhibitory according to the 
plain bouillon growth curve in fig. 11. An alkalinity corre- 
