1920] 
CHAMBERS— BACTERIAL INHIBITION BY METABOLIC PRODUCTS 251 
explained the death of organisms in culture as probably due 
rather to the exhaustion of the media and the accumulation of 
well-known metabolie products than to an “autotoxin.” He 
suggested the possibility of the exhaustion of the media and 
the accumulation of products causing the death of a few of the 
weaker individuals, which become self-digested, thereby releas- 
ing previously formed “autotoxin.” Acids and alkalis are re- 
ported by him as inhibitory agents, although bouillon in which 
pneumococci had grown would not support a second growth 
even on readjusting the reaction. 
In connection with some work on the latent period of growth, 
Chesney (716) found that pneumococci in plain broth showed 
marked inhibition 24 hours after inoculation, the number of 
bacteria decreasing rapidly to zero, but if after 96 hours a por- 
tion of the bouillon was filtered through a porcelain filter and 
reinoculated, no inhibition was evident, indicating that the 
inhibitory substance was killed or attenuated in 3 days at 37? C. 
It is apparent from the literature cited above that results 
are conflicting concerning the production of an enzymatic “auto- 
toxin," and while the reports favoring the existence of such 
a product are not conclusive, no other satisfactory explanation 
for the observed reactions has been demonstrated. 
Recent literature has indirectly contributed considerable of 
value concerning the relationship of acid and alkali to growth 
and death of bacteria, through the more general use, since 1916, 
of the hydrogen ion concentration as an expression of acidity 
of media. Winslow and Lochridge (006), working on Bacillus 
coli and Bacillus typhosus, stated that the toxic effect of inor- 
ganic acids, HCl and H.SO,, corresponded to their dissociation, 
but with organic acids, acetic and benzoic, the undissociated 
molecule was also important, for results did not correspond to 
the dissociation of the acids. Michaelis (14) advanced the 
idea that organisms produce acid to a certain concentration, 
which he found to be Px 5.0 with Bacillus coli in lactose bouillon, 
and that they automatically protect themselves against harm- 
ful amounts. 
Since that time a great deal has been published on final or 
limiting hydrogen ion concentrations for different organisms, 
