20 
standing exposed to the air its alcoholic solutions become more sensi- 
tive to oxidation by plant extracts. This can be readily accounted for 
on the supposition that on standing exposed to the air alcoholic solu- 
tions, both of aloin (particularly those which had been shaken with 
zinc dust) and guaiacum, absorb small amounts of oxygen with forma- 
tion of peroxides of some description, and that in the presence of the 
latter peroxidases, as well as oxidases, react to form the coloring mat- 
ter when such old solutions are brought in contact with plant extracts. 
In support of this conception may be mentioned the fact that aqueous 
solutions of the horseradish give no blue color with fresh tincture of 
guaiacum alone, whereas, as pointed out by Bach, this plant is partic- 
ularly rich in peroxidases. Hence it is very important to employ 
fresh solutions of aloin if correct conclusions are to be reached as to 
the presence or absence of oxidases in the extracts of living tissues. 
With ordinary precautions, however, aloin is an excellent reagent for 
the oxidases. 
THE ALOIX PEROXIDASE REACTIOX. 
As stated above, aloin, together with ozonized turpentine or hyro- 
gen peroxide, has been employed by Klunge and also by Schaer as a 
test for blood. This reaction undoubtedly depends on the presence 
of a peroxidase in the blood. With a solution of aloin in chloral 
hydrate and a 3 per cent solution of commercial hydrogen peroxide 
small quantities of the blood of a guinea pig produce a deep, wine-red 
coloration, which remains permanent for a considerable time. From 
a few preliminary observations with plant extracts, however, it 
appeared that aloin and hydrogen peroxide did give the peroxidase 
reaction. In order to test this point more thoroughly the following 
experiments were carried out with aqueous extracts of the fresh 
root of the horse-radish, which, according to Bach, is particularly rich 
in peroxidase. 
The fresh aqueous extract of horse-radish gave no reaction with 
guaiacum. On the other hand, with 3 per cent hydrogen peroxide and 
guaiacum, it gave a deep blue coloration, but with aloin and some of 
the same hydrogen peroxide it gave no coloration at all. It therefore 
occurred to me to repeat the work of Schaer on the peroxidase reaction 
with aloin and hydrogen peroxide, as furnished by extracts of the poke, 
Phytolacca decandra. Accordingly some of the leaves of this plant 
were mascerated with water and filtered. To the filtrate chloroform 
was added and the solution allowed to stand overnight. On the fol- 
lowing morning it was again filtered, wherebv a clear, vellowish solu- 
tion was obtained. This solution gave no test for oxidases, either with 
guaiacum or with the aloin solutions that had been employed through- 
out this work. On the other hand, on adding a small amount of a 3 per 
