L7 
for the oxidases. Since then similar studies have been carried out 
with various other leuco compounds and chromogenic substances. 
The following are the more important results that have been reached 
in these investigations: 
Leuco-rosolic acid. — The oxidation of this compound by certain plant 
oxidases has been studied by G. F. Mason and myself. The former 
obtained this compound in the form of beautiful transparent, color- 
less needles. In order to test its conduct toward the plant oxidases, 
a small amount of it was dissolved in a slight excess of sodium hydrox- 
ide. Two tubes were then prepared: N o. 1 contained 1 cc. of the 
solution of leuco-rosolic acid, together with 5 cc. of a freshly prepared 
aqueous extract of the skin of the potato; No. 2, same as No. 1, except 
that the aqueous extract of the potato had been boiled and then cooled 
to room temperature before it was mixed with the reagent. After 
standing one hour at ordinary temperature, 0.15 cc. N 5 sodium 
hydroxide solution was added to each tube. No. 1 became dark pur- 
plish red immediately, whereas No. 2 showed no trace of pink or red 
color. It was also observed that the potato oxidase oxidizes leuco- 
rosolic acid most rapidly in faintly alkaline solutions. Acid solutions 
and more strong!}" alkaline solutions of the compound were scarcely 
oxidized at all. 
Ethyl phenolphthalin. — This compound was prepared by Mason 
according to Baevers directions. In order to test its conduct toward 
the oxidases, tubes were prepared containing 5 cc. of active and boiled 
aqueous extract of the skin of the potato, respectively. To these tubes 
small amounts of ethyl phenolphthalin were added. At the end of 30 
minutes the tube containing the active extract developed a purple-red 
coloration on the addition of the alkali, whereas the boiled control 
gave only a slight yellowish-brown coloration. Other tubes were 
allowed to stand 18 hours. These showed a still more marked differ- 
ence in color on the addition of alkali. 
EthyV tetvabromphenolphthalin. — This compound was also prepared 
by Mason according to the method of Baeyer. It was found to be far 
more difficult to oxidize than the ethyl ester of phenolphthalin. In 
fact, with potato oxidase we did not succeed in oxidizing it at all, 
whereas on standing with certain of the organic peroxides, such as 
benzoyl peroxide and benzoyl acetyl peroxide (acetozone), it was oxi- 
dized with the production of a bluish-green coloration, but only slowly. 
The presence of bromine in this compound seems in some way to 
inhibit its oxidation by plant oxidases. 
Aloin. — A solution of this substance in alcohol and in an aqueous 
solution of chloral hydrate together with ozonized turpentine or 
hydrogen peroxide has been employed by Klunge and later by Schaer 
as a blood test. It would also appear from the work of Schaer that 
this substance is a general reagent for the peroxidases. Whether 
19948— No. 26—06 a 
