226 
CHARLES O. APPLEMAN 
relation of oxidase activity in the different juices examined. In 
another paper, Bunzel^ states: ''No matter what the derivation of 
the plant juice is, the relative oxidizability of the various compounds 
is approximately the same." 
Bunzel's^ apparatus, of the size now on the market, required very 
small amounts of juice for a determination of the oxidase in the tubers 
of the principal variety employed in this work. In order to avoid 
errors in the measurement of extremely small quantities of juice, 
resort was made to the following dilution method: 2 cc. of juice were 
measured into 10 cc. of distilled water and after thorough mixing, 
without violent shaking, 2 cc. of the dilution were placed in the long 
arm and 5 milligrams of oxidizable substance in the short arm of the 
apparatus. The determinations were made in a constant temperature 
box of 33° C. During the reaction the apparatus was shaken con- 
stantly at the rate of 180 complete excursions per minute. After 
repeated trials with the diluted juice, it was found that the rate of 
shaking within wide limits had no effect on the total amount of oxygen 
absorbed; but the velocity of the reaction seemed to be greatest at 
about the amount of shaking decided upon for the standard in this 
work.* 
The manometer readings recorded in this paper are those made at 
the end of one hour, unless otherwise noted, and represent the oxidase 
activity in .33 cc. of undiluted juice. Although in the case of pyro- 
catechin a very slow oxidation continued for several hours, it came to a 
comparatively definite end point after an hour. 
Catalase: The potato juice for the catalase determinations was 
prepared by grating the tubers with calcium carbonate in the manner 
described by the writer^ in a previous paper. The calcium carbonate 
neutralizes the free acids which very rapidly destroy the catalase 
in the juice. The catalase measurements were made in the same 
kind of apparatus used for the oxidase measurements, except that the 
apparatus was graduated to read positive pressures. The juice for 
a catalase determination was diluted in the following manner: 2 cc. 
of juice were added to 25 cc. of distilled water. The juice was thor- 
oughly mixed with the water by rotating the flask 25 times. One 
cubic centimeter of the mixture was carefully measured into the long 
arm of the apparatus and i cc. of Oakland dioxogen (hydrogen per- 
* The shaking machine is described in bulletin No. 191 from the Maryland 
Agricultural Experiment Station. 
