1920] 
CHAMBERS—BACTERIAL INHIBITION BY METABOLIC PRODUCTS 285 
sponding to Py 7.6-7.8 is comparable in toxicity with an acidity 
of Py 5.1. Bacillus coli seems more sensitive to small amounts 
of alkali than to small amounts of acid, for in the reversions 
of reaction in fig. 7, inhibition is evident shortly after crossing 
the neutral line, about Py 7.1-7.6. In a freshly inoculated 
culture without dextrose, fig. 7, inhibition is first noted about 
Pa 7.5. While the hydroxyl ions appear more toxic to Bacillus 
coli in less concentration than the hydrogen ions, they do not 
. Seem to be fatal in greater concentration, for death of the cul- 
ture was not observed on the alkaline side, although one culture 
containing CaCO,, which is not reported in the data, carried 
the Py to 9.5. 
The importance of the factors other than H or OH 1ons which 
may enter into the inhibition or killing of a culture of Bacillus 
coli is not overlooked, but it should not be over-emphasized. 
For example, in a 1 per cent dextrose bouillon culture, such as 
is shown in fig. 1 or 10, in addition to the H ions, the anions, 
formate, acetate, lactate, and succinate, are formed (Ayers and 
Rupp, 718), probably other anions, and also the undissociated 
acids. These add their inhibitory action to that of the H ions in 
producing death at Py 4.9, illustrated by fig. 10. The best growth 
curve, however, fig. 11, has only the hydrogen ion concentration 
controlled and in reality ferments much more dextrose than 
the 1 per cent dextrose culture of fig. 10. "The former culture 
ferments a total of over 1.36 per cent and none of the products 
are removed from the culture, while the latter does not ferment 
all of the 1 per cent dextrose furnished. It seems possible that 
the metabolic products other than the H ions are not sufficiently 
inhibitory to influence greatly the growth until the hydrogen 
ion concentration approaches the acid limit, but toward the 
critical acid zone their effect becomes noticeable. 
The growth curves as a whole do not agree exactly with the 
life phases presented by Buchanan (18). In fact, the diversity 
of growths produced by varying the hydrogen ion concentra- 
tion, as illustrated by fig. 11, is so great that one curve can 
express the growth of Bacillus coli in bouillon only when quite 
definite limitations. of conditions are imposed. In a growing 
eulture of an organism like Bacillus coli which produces acid 
from dextrose and alkali in plain bouillon, zrowth can be con- 
