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CHAMBERS—BACTERIAL INHIBITION BY METABOLIC PRODUCTS 253 
the initial Py; i. e., Pa 7.11 progressed to Py 5.70 and Py 4.96 
went to Py 4.68. He also showed a difference in critical Py 
according to the acid used, whether hydrochloric, acetic, or 
lactic acid. Wyeth (’19) extended his previous work and found 
in 2 per cent peptone that an initial range of Py 4.29-9.37 
gave a final range after 216 hours of Py 5.92-8.55, and that 
with an initial Py above 8.48 the production of acid exceeded 
that of alkali and the reaction approached Py 8.48. Indole 
formation was completely inhibited by dextrose, partially by 
sucrose, and not at all by starch. Avery and Cullen (719) used 
the final hydrogen ion concentration to separate strains of 
Streptococcus hemolyticus; 124 human strains attained a final 
Py of 4.8-5.3, while 40 dairy strains reached Py 4.3-4.5. 
Considerable work has recently appeared on the pneumo- 
coccus. Cullen and Chesney ('18) showed the relation of the 
growth of pneumococcus in plain broth to hydrogen ion con- 
centration. The bacteria increased to 420,000,000 per cc. in 
13.8 hours and then decreased to 160 per ec. in 96 hours. The 
hydrogen ion concentration increased from P; 7.70 to Py 7.03," 
but these investigators expressed the opinion that the increase 
in hydrogen ion concentration is not the sole cause of the cessa- 
tion of growth. Avery and Cullen (19) showed some inter- 
esting reactions of pneumococcus to carbohydrates. One per 
cent of maltose, saccharose, lactose, galactose, raffinose, dex- 
trose, or inulin produced a final Py of about 5.0. With .4 per 
cent dextrose, as high an hydrogen ion concentration was at- 
tained in 48 hours as with 1 or 2 per cent dextrose.  Pneu- 
mococcus differed from Bacillus coli in that it produced acid in 
plain broth, and growth ceased at about Pu 7.0. When this 
culture was readjusted to Py 7.8 and reinoculated, no growth 
occurred unless carbohydrate was added, yet the filtrate from 
a dextrose culture at Py 5.2 if readjusted to Py 5.8, 7.0, or 8.0 
would again return to Py 5.2. Growth could only be initiated 
within certain limits, in carbohydrate media Py 8.3-6.8 
and in plain broth Py 8.1-7.0. They concluded that the 
exhaustion of fermentable carbohydrate is only one of the many 
1To avoid confusion, attention is called to the distinetion between the concen- 
tration of the hydrogen ions and the symbolic Pu. A numerical increase in hy- 
drogen ions is expressed as a decrease in terms of Pu. 
