roi] APPLEMAN—AFTER-RIPENING OF POTATO 309 
method, morphologically similar parts of the tuber were sliced 
directly into absolute alcohol and heated to 70° C. for 10 minutes 
in order to destroy the oxidases. The slices were allowed to 
remain in alcohol 24 hours. The alcohol was changed three times. 
They were then dried between filter paper, covered with ether for 
a few minutes, replaced between filter paper, quickly dried in a 
vacuum desiccator, and thoroughly pulverized in a mortar. One 
gram of this powder was ground one minute with quartz sand and 
25 Cc. water and filtered. For the tests 5 cc. of the filtrate were 
used and 0.5 cc. of guaiaconic acid sdlutics and o.1 cc. of one-half 
per cent hydrogen peroxide. The guaiaconic acid solution was 
Prepared by dissolving 0.5 gram of guaiaconic acid in 50 cc. 
alcohol. 
Three sources of error were soon discovered in this method of 
extract preparation, which render it unreliable for comparative 
purposes. Filtering, which is necessary in order to obtain a 
sufficiently clear solution for colorimetric work, removes a large 
percentage of the peroxidase. This is probably due to inclusion 
of the peroxidase in the clot of coagulable proteins, and not to an : 
insoluble form of the enzyme. Filtering has no effect on the 
peroxidase activity of fresh unheated extract. 
TABLE I 
Errecr OF FILTERING ON PEROXIDASE ACTIVITY OF HEATED EXTRACT 
| 
SECONDS REQUIRED FOR REACTION TO REACH STANDARD TUBE 
HEATED To 70° C. for 10 MIN. | | 
| Filtered through Filtered through 
Unfiltered cotton paper 
Ste ce RE ee = 28 56 
Pee eae | 12 23 
ample 3... | 
el oe 15 45 
crs es ieee ek | 15 35 
aN } pens en 
Another source of error probably arises also from the presence 
of coagulable proteins. The peroxidase leaches out of the 
Coagulum and thereby renders the peroxidase activity of the 
solution very unstable, as shown in table II. HasseLBRING and 
ALSBERG (5) found a similar condition in studies upon oxidases, 
and first concluded that it must be due to coagulable proteins. 
