1915] ROSE—APPLE BARK 63 
On the nineteenth day the negative pressure was released, all the 
apparatus closed again, and the test continued for three days more. 
The results are shown in table VI. 
TABLE VI 
Healthy Diseased , 
Before releasing. «. .....4544 1oth day of test —2.03 —2.46 
Alter releasing... 6s cscs. ROG 2 aie 0.00 0.00 
= Mins ale Pee sah Sei —0.12 —o.08 
™ OA aa yg IRE gage oe Mamita ae i —0.15 —o.1I 
Average of 2 Average of 2 
Table VI indicates that oxygen supply is a limiting factor as 
well as acidity. Its importance should be investigated further. 
On the twenty-first day, when the experiment was finally closed, it - 
was found that the mixture from the two apparatuses containing 
healthy bark extract and from the other two containing diseased 
bark extract had increased from an original acidity of o.38 in the 
first case, and 0.28 in the second case, to 0.50 in both (acidity 
expressed here as before in terms of cc. of n/2o NaOH necessary 
to neutralize to phenolphthalein). Similar results were obtained 
in two other experiments in which the reaction had come to an end. 
It thus appears that the gradual slowing down of the rate of 
oxidation in these experiments and in others conducted with similar 
apparatus is due to increasing acidity and not to chemical com- 
bination of the oxidase with some substance in solution, as suggested 
by BunzEt (2, p. 39). If this be true, the evidence is strong that 
oxidases are true catalytic agents, prevented usually from bringing 
about indefinite catalysis by the presence or absence of something 
which acts as an inhibitor. It is probable that just as enzyme 
hydrolysis of carbohydrates and other substances reaches a con- 
dition of equilibrium because of accumulation of the products of 
hydrolysis, in exactly the same way, in the BuNzEL apparatus at 
least, oxidation ceases because of inhibition by accumulated oxida- 
tion products. These will include carbon dioxide and acetic and 
oxalic acids if the decomposition of pyrogallol by oxidase is like 
that induced by alkalies and the salts of heavy metals. In the 
presence of O, alkalies cause pyrogallol to turn brown with the 
