78 
the agency of the ferment. This view of the mode of action of tyro- 
sinase has recently been disproved by Bach ( 25 ), who has shown that 
tyrosinase does not produce black pigments from mixtures containing 
such substances as might be produced by the hydrolysis of tyrosin, 
such as phenol + d + 1 serin, liydroquinone + alanin, p-cresol + oxya- 
mino-acetic acid, and p-oxy-benzyl alcohol + glycocoll. 
Gonnermann’s hypothesis respecting the mode of action of tyrosi- 
nase has also been refuted by Chodat and Staub ( 117 ) . The results of 
their experiments in an atmosphere of carbon dioxide show clearly 
that oxygen is required for the process and that the action of the 
ferment is not simply the production of an easily oxidizable substance 
by the hydrolysis of tyrosin. 
We have seen that according to Gessard ( 181 > 189 ), the action of tyro- 
sinase on tyrosin consists of two distinct processes, first, the oxidation 
of tyrosin to a red substance, and, second, the condensation of the red 
substance to a black product (melanine). The oxidation can be 
accomplished either by tyrosinase in the presence of air, or by a chem- 
ical oxidizing agent such as Millon’s reagent, whereas, for the conden- 
sation of the red substance into the black pigment, the action of the 
mineral salts contained in the tyrosinase are necessary. This hypothe- 
sis respecting the mode of action of tyrosinase has recently been 
refuted by Bach ( 25 ). In order to throw further light on this subject, 
he prepared an active solution of tyrosinase and heated it to boiling. 
After cooling, tyrosin was added to the solution, and 20 c. c. portions 
of it were placed in four reagent glasses. To the first of these there 
was then added 5 c. c. of water, to the second 2 c. c. of 1 per cent 
hydrogen peroxide and 3 c. c. of water, to the third 2 c. c. of 1 per 
cent hydrogen peroxide solution, 2 c. c. of a peroxidase solution, and 
1 c. c. of water, and to the fourth a solution of an oxidase prepared 
by heating an extract of Lactarius vellereus to 75° C. to destroy the 
tyrosinase. These tests remained colorless for weeks, indicating that 
the oxidation of tyrosin by tyrosinase is not referable to the inor- 
ganic substances which it contains. Bach also sought in vain for a 
co-ferment of tyrosinase among plants. He concludes, therefore, that 
the oxidation of tyrosin only takes place through the action of perox- 
idases, hydrogen peroxide, plant juices, or ferment preparations when 
the preparation itself is active to tyrosin, that is, when it contains tyro- 
sinase. Indeed, it would seem from his most recent utterances on the 
subject that Bach (ibid.) is inclined to look upon the action of tyrosi- 
nase as completely different from that of the common oxidases (perox- 
idase + hydrogen peroxide) . Tyrosinase, he says, belongs to a peculiar 
class of oxidizing ferments, whose oxidizing action is exerted upon 
substances containing slightly labile hydrogen. 
Formerly all observations upon the action of tyrosinase were quali- 
tative in character, being confined to rather crude and indefinite color 
