79 
comparisons. Recently, however, three quantitative methods for 
determining: the quantity of pigment resulting from the action of 
tyrosinase on tyrosin have been proposed. These are (1) a spectro- 
photometric method. (2 ) a sedimentation method, and (3 ) a volu- 
metric method by means of a 0.002X solution of potassium perman- 
ganate. The first two methods were proposed by Von Furth and 
Jerusalem ( 17S ). For details concerning these methods and the use of 
the instrument, with which the writer is not familiar, the original 
article may be consulted. Fu this connection see also Morner ( 307 ). 
The second method of Von Furth and Jerusalem ( 17S ) depends upon the 
sedimentation of the pigment by boiling with a small amount of cal- 
cium chloride. After boiling a short time the beakers or tubes con- 
taining the substances are allowed to stand, when ihe black pigment 
settles out, leaving the liquid clear. The clear supernatant liquid is 
then poured off and the residue washed with water and transferred 
to a graduated centrifuge tube by means of water, centrifueed and 
measured. The third method was first employed by Bach ( 23 ), and 
depends upon the fact that the brown pigment formed by the action 
of tyrosinase on tyrosin can be oxidized by a dilute acid solution of 
permanganate, 0.002X, to a colorless compound. Hence in order to 
determine the quantity of pigment produced in a given time by the 
action of tyrosinase on tyrosin. the black mixture is titrated with 
0.002X permanganate, after the addition of sulfuric acid, until the 
color of the titer disappears. 
Of the three methods, Bach's is the simplest and commends itself 
most strongly to chemists. It requires no special apparatus, and by 
its use he (Bach obtained far more regular and generally concordant 
results than Von Furth and Jerusalem were able to obtain with the 
spectrophotometric and sedimentation methods. See Bach 24 ). 
THE KINETICS OF MELANINE FORMATION BY TYROSINASE. 
The quantitative methods devised by Von Furth and Jerusalem ( 17S ) 
and by Bach f 23 ) have already been utilized by these observers and 
also by Chodat and Staub ( 117 ) in studying the kinetics of the tyro- 
sinase process. According to the latter the velocity of the reaction 
at small concentrations is proportional to the quantity of ferment 
present. At greater concentrations the rate of the reaction has been 
found equal to the algebraic expression, Kc — b, in which c is the con- 
centration. and K and b are constants. Von Furth and Jerusalem 
( supra 1 have investigated the effect of temperature, quantity of fer- 
ment, and the influence of hydrogen peroxide, alkalinity, and inor- 
ganic catalyzers on the kinetics of melanine formation by vegetable 
and animal tyrosinase. 
Von Furth and Schneider ( 17S ) found the tvrosinase of insect blood 
to be exceedmgly sensitive to the prolonged action of high tempera- 
