80 
tures. Thus a long exposure to 30° C. is sufficient to inhibit the action 
of the ferment. In order to determine the effect of temperature on 
the action of vegetable tyrosinase (from Agaricus melleus) Yon Furth 
and Jerusalem prepared four tubes, each of which contained 4 c. c. 
of the tyrosinase solution, 60 c. c. of an alkaline solution of tyrosin, 
and 2 c. c. of 3 per cent hydrogen peroxide. These tubes were labeled 
a, b, c, and d; a was kept at 5°-7° C., b at room temperature, c at 40° 
C., and d at 55° C. At the end of half an hour a and b were not 
noticeably altered in appearance; c was darker, and d was the darkest 
in color. The next morning a and b were colored black, c was lighter, 
and d was the lightest in color. The quantities of melanine in the 
four tubes as determined by the spectrophotometric method were 
found to stand in the following ratio: 
a = 1.29; b = 0.55; c = 0.42; and d = 0.22. 
These authors conclude, therefore, that so far as the influence of tem- 
perature on the production of melanine by the action of tyrosinase 
is concerned, two opposing processes are at work, viz, the accelerat- 
ing effect of temperature common to all chemical reactions and the 
destructive action of temperature on the labile ferment. The result 
is that the process reaches an equilibrium between 30° to 50° C., and 
that between 60° and 65° C. the ferment ceases to act on the tyrosin. 
The effect of small amounts of hydrogen peroxide is to increase the 
quantity of melanine produced by tyrosinase in a given time, whereas 
larger quantities of the peroxide exert a retarding effect on the proc- 
ess. Roughly, the quantity of melanine formed by the action of a 
given amount of the ferment acting under the same conditions was 
found to be proportional to the concentration of the tyrosin. Within 
narrow limits of concentration (0 to 10 c. c. of 0.04 per cent sodium 
carbonate solution in a total dilution of 27 c. c.) the effect of alkali 
was found to be practically negligible. Within certain limits the 
quantity of melanine formed increases with increase in the concen- 
tration of the fungus tyrosinase. Thus the effect of doubling the 
quantity of ferment was to cause an increase in the production of 
melanine from 1.0 to 1.4. On the other hand, the addition of further 
amounts of the ferment caused no increase in the production of mel- 
anine; in fact, a slight diminution in the quantity of melanine oc- 
curred, indicating that increasing quantities of the ferment above 
certain limits cause a retardation of the process. 
With animal tyrosinase (from the hemolymph of Deiciphila euphor- 
biae ) the rate of melanine formation was considerably increased by 
an increase in the quantity of hydrogen peroxide present, but in 
the end very nearly the same amounts of melanine were produced in 
all cases. Acids, even the weakest, were found to prevent the action 
