1904.] Tyrosinases in the Skins of Pigmented Vertebrates. 311 



be obtained from the skins of these animals, pigmented substances 

 corresponding in colour to those of the animals taken, could be formed 

 by the action of the ferment upon tyrosin or allied bodies. 



I chose, for this purpose, the skins of young or foetal animals, 

 because these are in a condition of active pigment-formation. The 

 study of adult forms shows that the older animals moult gradually r 

 and that they would, therefore, in all probability, yield less material. 



As young mice are very small, I preferred to use new-born rabbits 

 and rats (of black or agouti origin) and foetal guinea-pigs (about 

 8 weeks). In the case of the guinea-pigs, the skins of the mothers 

 were also used for comparison. 



The skins, having been removed from the animals, were chopped in 

 a sausage-machine, and ground in an agate mortar with kieselguhr 

 and distilled water. The use of this mortar was kindly permitted to- 

 me by Professor Sims Wood head. The ground-up skins were then 

 pressed out as completely as possible. 



The expressed juice was red, and opaque in appearance. A portion 

 of it was placed in a test-tube with solid tyrosin, and a milligram of 

 ferrous sulphate was added as an activator. Toluol was then added 

 as an antiseptic, and the tube was closed with cotton-wool, and placed 

 in an incubator at 37 C. 



For comparison, a series of tubes were prepared, in order to control 

 the experiment. In the first tube boiled juice was placed, to which 

 tyrosin and ferrous sulphate were added. In the second tube juice only 

 was placed. The third tube contained juice, to which tyrosin was 

 added. The fourth tube contained the juice, with a milligram of 

 ferrous sulphate. The fifth tube contained no juice, but tyrosin in 

 distilled water, with ferrous sulphate. These tubes were all placed in 

 the incubator. 



A similar series of tubes was also prepared, and kept at the ordinary 

 temperature of the laboratory. A tube containing juice, tyrosin, and 

 ferrous sulphate was also prepared, and kept at the laboratory tem- 

 perature. In every case, toluol was used as an antiseptic. Cotton- 

 wool was used to close the tubes, on account of the action of iron 

 upon cork, which might introduce an error into the result. 



In 24 hours, the contents of the tube, which was incubated, 

 containing the juice, tyrosin, and ferrous sulphate showed a change in 

 appearance. The fluid had darkened and a black substance was 

 deposited; the amount of this substance increased as time went on. 

 In no case did any of the other tubes arranged to control the experi- 

 ment show any such change. 



In one case, when considerable juice had been obtained from a 

 number of young black rabbits, about 2 days old, a certain quantity of 

 the juice was kept, in order to test the effect of time upon it. After it 

 had been tested, it was kept standing for two days and fresh tubes 



