[Vor. 7 
256 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
TABLE I 
GROWTH AUD HYDROGEN ION CONCENTRATION OF Mo. COLI IN 
AIN AND 1 PER CENT DEXTROSE BOUILLON AT 3 
2 
puer Plain bouillon and 
Plain bouillon 1% dextrose 
Hours 
Bacteria per cc. Pu Bacteria per cc. Pn 
0 54,000 7.1 55,000 7.4 
12 175,000,000 6.8 268,000,000 5.3 
20 281,000,000 5.1 
24 320,000,000 7.2 214,000,000 4.9 
36 538,000,000 7.5 220,000,000 4.8 
48 609,000,000 7.6 189,000,000 4.8 
72 450,000,000 V 119,000,000 4.8 
96 459,000,000 7.8 14,500,000 4.9 
120 293,000,000 7.9 100 4.9 
144 250,000,000 8.1 0 4.9 
168 151,000,000 8.1 
192 156,000,000 8.3 
234 125,000,000 8.2 
276 115,000,000 8.3 
348 89,000,000 8.3 
492 69,000,000 8.3 
612 71,000,000 8.3 
1284 53,000,000 8.5 
1800 7,500,000 8.7 
ture of 30% C. was maintained for all cultures throughout the 
work. 
The changes in growth and hydrogen ion concentration in 
each culture were followed by removing, under aseptic con- 
ditions, a 3-cc. sample at 12- or 24-hour intervals, after the flasks 
had been rotated briskly 30 times to mix the contents thor- 
oughly. One ec. was diluted and plated in triplicate in agar 
composed of plain bouillon to which 1 per cent dextrose and 
1.5 per cent granular agar had been added. The hydrogen 
ion concentration was determined from the remaining 2 cc. 
according to the colorimetric method of Clark and Lubs (’17), 
using the micro-colorimeter described by Duggar ('19). The 
hydrogen ion concentration is expressed in Pu, or the reciprocal 
values of Sórensen now in general biological use. Plates were 
counted after an incubation of 72 hours at 30? C. 
