19 
by the oxidation of the aloin is much more stable than the blue com- 
pound produced by the oxidation of the guaiacum. Secondly, the 
red coloring matter resulting from the oxidation of the aloin is soluble 
in water and in aqueous extracts containing the oxidases. It has been 
found, therefore, that alcoholic aloin is a very delicate reagent for 
oxidases, especially when it is poured into the tube containing the 
aqueous extract of the plant in such a way as to prevent the mixing of 
the two liquids. 
Under these circumstances the aloin takes on a red color at the zone 
of contact of the two solutions, and in this manner it has been found 
possible to recognize very small amounts of oxidases, such small 
amounts indeed that their presence in the solution would have been 
doubtless overlooked by the ordinary methods employed in testing for 
these substances. On the other hand, as a reagent for the oxidases, 
aloin also possesses certain disadvantages; especially is this true of 
the alcoholic solution that has been treated with zinc dust. While 
such solutions become very sensitive after a short exposure to the air, 
after several days’ exposure they seem to lose their power of reacting 
with the oxidases altogether. That such is the case is evident from 
the conduct of the following aloin solutions toward fresh aqueous 
extracts of the horse-radish, Nasturtium armoracia: 
(1) Freshl} 7 prepared alcoholic aloin. 
(2) Same as (1), except that it had been shaken with zinc dust and 
filtered. 
(3) Same as (2), except that it had been prepared several days before 
being used. 
0.5 cc. of solutions (1) and (2) and (3), respective^, were added to 
2 cc. of a freshly prepared aqueous extract of horseradish root with 
the following results: 
(1) Remained yellow after standing. 
(2) Light reddish-brown in color, lighter than (3). 
(3) Wine red. 
These results were duplicated in another extract. 
The activity of these solutions was also tested toward a fresh aqueous 
extract of potato oxidase, with the following results: 
(1) Color quite slow in developing — faint pink. 
(2) Deep wine-red, almost instantly. 
(3) Followed (2) in order of activity. 
Control experiments with the boiled extract of the potato gave only 
a slight pink with (2) on standing for some time. Finally an alcoholic 
solution of aloin that had stood at room temperature for two days, 
and which originally had been found to be very active toward oxi- 
dases, was found to have become reddish-brown in color and to have 
lost its ac^vity toward oxidases to a great extent. It would seem, 
therefore, that aloin is ver} 7 much like guaiacum, in the sense that on 
