21 
cent solution of hydrogen peroxide to some of the clear extract, and 
then aloin or guaiacum, a good test for peroxidase was obtained with 
both reagents. 
It was further showm by these experiments on the clear extract of 
Phytolacca decandra that better peroxidase reactions could be obtained 
with aloin by using very small amounts of hydrogen peroxide. In 
order to test this point more thoroughly five tubes were prepared, 
each containing 2 cc. of the aqueous extract of Phytolacca decandra. 
To (1) there was added no hydrogen peroxide, to (2) 0.1 cc. of hydro- 
gen peroxide, to (3) 0.2 cc., to (1) 0.3 cc., and to (5) 0.1 cc. of 3 per 
cent hydrogen peroxide. To each of these tubes there was then added 
0.5 cc. of a solution of aloin in 10 per cent chloral hydrate solution 
with the following results: 
1. Yellow in color. 
2. Very deep wine-red. 
3. Wine-red, lighter than (2). 
4. Red, lighter than (3). 
5. Light pink, lighter than (4). 
These experiments were repeated, using 3 per cent hydrogen perox- 
ide that had been diluted with ten volumes of water. With hydrogen 
peroxide of this dilution no great differences were observable in the 
color of the tubes, all of them except (1) being deep wine-red. These 
results go to show that the intensity of the aloin peroxidase reaction, 
as shown b} 7 Phytolacca decandra , is clearly dependent on the concen- 
tration of the hydrogen peroxide, and but little differences are observ- 
able in the intensity of the reaction, provided very small amounts of 
hydrogen peroxide are employed. It therefore seemed to be advis- 
able to repeat the work on the extract of the horse-radish, using 
hydrogen peroxide of greater dilution than had hitherto been 
emplo} 7 ed. Accordingly, a fresh aqueous extract of the root of the 
horse-radish was prepared. With this four tubes were prepared, 
each containing 2 cc. of the extract. To these the following amounts 
of 0.3 per cent hydrogen peroxide were added: To (1), none; to (2), 
0.1 cc. ; to (3), 0.2 cc. ; to (4), 0.3 cc. To each of these tubes there 
was then added 0.5 cc. of a solution of aloin in 10 per cent chloral 
hydrate, with the following results: 
(1) Yellow in color. 
(2) , (3), (4) became deep wine-red, in the order named. 
Similar experiments were carried out with an aqueous extract of 
the skin of the potato, which had stood several hours and which had 
lost the power to give the guaiacum reaction for oxidases. With this 
extract three tubes were prepared, using 2 cc. of the extract. To 
these the following amounts of 0.3 per cent hydrogen peroxide were 
added: To (1), none; to (2), 0.1 cc., and to (3), 0.2 cc. To each tube 
