Igtt] APPLEMAN—AFTER-RIPENING OF POTATO Sit 
ground in a mortar with quartz sand for two minutes, and the 
extract pressed through cotton and cheesecloth; 1 cc. of the 
extract was at once added to 300 cc. of water. This dilution gave 
a solution sufficiently clear for the test and a speed of reaction 
which reached the standard color in less than a minute. It was 
unnecessary to destroy the oxidase by heating. In this dilute 
solution the time required for the oxidase to produce a visible 
blue was longer than that required for the peroxidase to produce 
the blue of the standard color. 
TABLE IV 
EFFECT ON PEROXIDASE ACTIVITY OF EXTRACT WHEN THE POTATO TUBER 
IS GRATED WITH CaCQ, 
SECONDS REQUIRED FOR REACTION TO REACH 
BLUE OF STANDARD TUBE 
PoTATO TUBER 
| After 6 hours | After 24 hours 
Ground with CaCO, ....... 21 21 3° 
Ground without CaCO,..... 45 bs go 
OxIpAsE.—Colorimetric methods, as well as the direct measure- 
ment of the oxygen consumed by the oxidation of hydrochinon 
in the manner recommended by Griiss (2), were used in an effort 
to ascertain the comparative rate of oxidase activity. So many 
sources of error were discovered in applying these methods to the 
material under investigation, that the results were considered too 
unreliable for publication. Better methods than those in present 
use are much needed. 
Experiments 
In comparing results obtained by the two methods for peroxi- 
dase determinations previously described, it was found that the 
alcohol and ether method always gave a much greater peroxidase 
activity in the cold storage potatoes than in those stored at room 
temperature, while the fresh extract method gave practically the 
Same in both cases during the same period of storage. According 
to the following table this would seem to be due to an alteration 
at low temperature of coagulate protein, which modifies the 
