1920] 
CHAMBERS—BACTERIAL INHIBITION BY METABOLIC PRODUCTS 287 
SUMMARY 
Growth and death of Bacillus coli in the culture bouillon of 
these experiments does not follow a constant curve but is de- 
pendent on the hydrogen ion concentration of the medium. 
The hydrogen ion concentration of a growing culture of Bacillus 
coli is controlled by the composition of the medium, and par- 
ticularly by the amount of fermentable carbohydrate present. 
The maximum count, determined by the plate method, in the 
culture with the hydrogen ion concentration controlled is 3,750,- 
000,000 bacteria per cc., as contrasted with a maximum of 
281,000,000 bacteria per cc. in the 1 per cent dextrose bouillon 
with the hydrogen ion concentration uncontrolled. 
No investigation was made of the limiting influence of other 
factors, such as aération, on the maximum number of bacteria 
per cc. in the culture where the hydrogen ion concentration 
was controlled. 
No metabolic product of the nature of an “autotoxin” could 
be found. 
Of the products of metabolism, acid is the most inhibitory, 
checking growth slightly at Py 5.5 and increasing in intensity 
to a lethal concentration between Pg 5.1 and 4.9. 
The first inhibition on the alkaline side is noted between 
Pa 7.0 and 7.6, depending on the age of the culture and other 
factors. Pg 7.6 is comparable in inhibitory action to Py 5.1. 
In an asparagin-CaCO, bouillon, Px 9.5 is not fatal. 
'The inhibitory action of the metabolie products of dextrose 
other than the hydrogen ions is only evident near the critical 
acid concentration. 
To Dr. B. M. Duggar the writer is deeply indebted. His 
aid and suggestions throughout the investigation have been 
invaluable. 
BIBLIOGRAPHY 
Avery, O. T., and Cullen, G. E. (19). Use of final Pg in differentiation of Strep- 
tococcus hemolyticus. Jour. Exp. Med. 29: 215-233. 1919. 
————, —————, (19). Hydrogen i ion concentration of cultures of pneu- 
mococci of the different types in carbohydrate media. bid. 30: 359-378. 
1919. 
