[Vor. 7 
254 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
faetors involved in the complex phenomenon of growth inhi- 
ition. 
Lord and Nye (19) have demonstrated the relation of time 
to inhibitory action of hydrogen ion concentration with pneu- 
mococcus. They found that Pneumococcus Type I was killed 
in 1 hour at Py 4.5-4.7, in 3 hours at Py 5.3, and in 6 hours 
at Py 6.15, but survived 6 hours at Py 6.35, and that between 
Py 6.8 and Py 5.1 there was a direct relation between the Py 
and the time required for the death of the pneumococcus. In 
mixtures of equal quantities of emulsions of washed pneumo- 
cocci and buffer solutions of different hydrogen ion concentra- 
tions they observed very little dissolution of the bacterial cells 
between Py 8.0 and Py 7.0 or between Py 5.0 and Py 4.0, but 
noticed almost complete dissolution in the zone of Py 6.5- 5.5. 
Bunker ('19) published the results of investigations of Bacillus 
diphtheriae extending over several years. The hydrogen ion 
curves in sugar-free and in 1 per cent dextrose media agree 
very closely with those of Bacillus coli in the experimental work 
of this report. He also showed that toxin was only produced 
within a rather narrow hydrogen ion range, Py 7.8-8.25. 
The best growth, measured by pellicle formation, was obtained 
when the initial reaction was Py 7.3-7.5. Cohen and Clark 
(19) investigated the effect of hydrogen ion concentration on 
the rate of growth of different organisms during the early part 
of the growth curve, the period of logarithmic increase. Cul- 
tures were inoculated into media adjusted over a wide range of 
varying initial hydrogen ion concentrations, and observed for 
the first 10 hours of.growth. In general, the different organ- 
isms reacted similarly. The most marked effect of the hydrogen 
ion concentration on early growth was found near the critical 
acid and alkali zones. They reported that with Bacillus coli 
fermentative activity was checked in 1 per cent dextrose bouillon 
at Py 5.0, but that growth in plain bouillon was checked at 
Py 5.7. They noted evidence of inhibition which obscured their 
results, but they did not study the inhibitory factors; however, 
it was found that the period of lag was more pronounced in 
alkaline than in acid media. 
Recent contributions from Besson, Ranque, and Senez (719), 
while they do not involve hydrogen ion concentration, advance 
