21 
It may be added that ammonium oxalate (5 per cent) had no dele- 
terious effect upon oxidase after two days; but nicotine tartrate in a 5 
per cent solution, and quinine acetate in a 0.5 per vent solution, seemed 
to damage the oxidase after four days, although but very little. 
KILLING TEMPERATURE OF OXIDIZING ENZYMS. 
The temperatures thus far observed which render enzyms inactive 
are not constant under all conditions; the acidity of the plant juice, 
the degree of dilution, the duration of the heating, and the presence 
of certain salts have a modifying influence on the height of the tem- 
perature at which the change to the inactive modification takes place. 
It is to be regretted that authors have not always mentioned the con- 
ditions and the duration of the heating. The oxidase of the stalks of 
the sugar cane is killed at 60° C. (140° I.), the peroxidase of it at 95° C. 
(203° F.), according to Raciborski. Tyrosinase, an oxidase easily oxi- 
dizing tyrosine to a dark substance, is injured at 50° C. (122° F.) and 
killed below 70° C. (158° F.), according to Bertrand. Laccase, an oxi- 
dase of widespread occurrence, is killed at 63° C. (145.4° F.), Oenoxi- 
dase loses haif of its oxidizing power at 72° C. (161.6° F.) within four 
minutes, and at 55° C. (131° F.) in one and one-half hours. The oxi- 
dase of mammalia is killed at from 80° to 85° C. (Abelous and 
Biarnes.) 
The influence of the duration of the heating is shown by the follow- 
ing test. The killing temperature of the oxidase in the juice of the 
tobacco leaf was repeatedly found to be from 66° C. to 67° C. when 
the juice was diluted (one part dried ieaf to twenty parts of water) 
and the solution heated for three minutes. But in heating it for a 
second only a much higher temperature may be endured. Certain 
salts, as ammonium sulphate, and also traces of free ammonia, increase 
the resistance, while acids, even in smaili quantities, decrease it. The 
juice of the midrib contains less acid than that of the lamina, and con- 
sequently it takes a temperature several degrees higher to kill the 
oxidase in the former than in the latter, but on being neutralized the 
latter may be safely heated for a moment to 75° C. The addition of 
alcohol decreases the power of resistance. Thus an addition of 33 per 
cent of alcohol to a neutralized solution of oxidase will depress the 
killing temperature about 2° C. 
The following tests were made with peroxidase: Fresh tobacco leaves 
were ground, with the addition of some sand and a little water, and 
the pulp expressed. The residue was now left for some hours in con- 
tact with water to which 0.5 per cent acetic acid was added, and 
expressed again. The filtrate thus obtained was exactly neutralized 
with dilute caustic soda. It gave only avery faint reaction for oxidase, 
but an intense reaction for peroxidase. To one portion (20 ¢. c.) was 
added one-half its volume of absolute alcohol; to another 10 per cent 
of ammonium sulphate. Upon heating in a water bath it was found 
