322 
Journal of Agricultural Research 
Vol. XI, No. 7 
Next, in order to show whether the hydrocyanic acid destroys or com¬ 
bines with the enzym and exerts its effect even after the poison has been 
removed and when it is not present during the oxidase reaction, the 
following experiments were performed: 0.4 gm. of leaf powder on a watch 
glass was made into a paste with 1.0 c. c. of the hydrocyanic-acid solu¬ 
tion to be tested, covered with another watch glass and allowed to stand for 
varying lengths of time; then placed in a vacuum desiccator for 24 hours. 
After powdering it 
in a mortar it was 
sieved through No. 12 
silk bolting cloth and 
used for oxidase de¬ 
termination, as in the 
original powder. The 
results are shown in 
figure 2. The curves 
indicate that there is 
no permanent injury 
to the oxidase activity 
of these powders fol¬ 
lowing treatment with hydrocyanic acid, and that if there is any 
change at all it is a slightly increased activity. 
To show the effect of fumigation with hydrocyanic acid on the oxidases 
of tomato plants (Lycopersicon esculentum), a group of plants about 30 
cm. high was divided into two sets. One set was fumigated with 1.0 
gm. of potassium cyanid per cubic meter for one hour in the middle of 
the day; the other group was held as normal. At stated intervals before 
and after fumigation samples consisting of the upper three leaves of the 
plants (since the younger leaves always show effects of fumigations more 
Fig. i.—C urves showing in two samples of tomato leaves the effect on 
oxidase activity of the presence of hydrocyanic acid during the 
determination. 
— 
— D 
T- 
£ 
30 
I/O 
or //c/v 
Fig. 2.—Curves showing the oxidase activity of leaf powders treated with varying concentrations of hydro¬ 
cyanic-acid solution, the latter haying been removed before the determination was made: A, treated rs 
minutes before desiccation; B, C t D, E, treated 2 hours before desiccation. 
and contain the more active oxidases) were taken and prepared in the 
powder form for analysis. The data are shown in the upper curves of 
figure 3. There is a sudden and striking drop in oxidase activity exhib¬ 
ited by the fumigated group at the close of the fumigation. This is 
followed by a rapid recovery to normal within 13 hours. The experi¬ 
ment was repeated with a second group of plants with similar results, as 
shown in the lower curves of figure 3. In this case the recovery was even 
more rapid, being complete in two hours. 
