264 SCIENCE PROGRESS. 



up the blackening. Nor will simple oxidising agents bring 

 it about. That it is an oxidation process due to the presence 

 of a special oxidase is asserted by Bertrand, who has named 

 the oxidase in question tyrosinase (15). 



If to a solution of tyrosin a little of the cold water 

 extract of Russula nigricans is added, the mixture becomes 

 at first red, and then later assumes an inky blackness, while 

 finally a black amorphous precipitate settles out. If this is 

 carried out in a glass vessel without agitation, the colour 

 first appears at the surface of the liquid. If it is conducted 

 in a closed vessel from which air is excluded the change of 

 colour does not take place. Nor is the change induced if 

 the extract of the fungus is boiled before being added to the 

 solution of tyrosin. In a closed vessel in the presence of 

 air, the absorption of oxygen can be measured coincidently 

 with the blackening of the liquid. 



Tyrosinase can be extracted not only from Russula 

 but from the dahlia and the beet root. It is immaterial 

 which of the three serves as the source of the oxidase, 

 as the effect upon the tyrosin is the same in all cases. 

 Russula appears to contain it in greatest quantity. The 

 same mode of extraction can be employed with either 

 material. 



In some species of Russula the two oxidases so far dis- 

 cussed exist side by side. Bertrand has separated them by 

 the following treatment (5) : One and a half kilogramme of 

 freshly gathered Russula delica Fries, was reduced to pulp 

 and macerated for half an hour with its own weight of 

 chloroform water at the ordinary temperature. On pressing 

 it, about two litres of a mucilaginous fluid were obtained, to 

 which three litres of 95 per cent, alcohol were added. A 

 precipitate fell which was filtered off. The liquid was con- 

 centrated to half a litre by distillation at 50° C. in vacuo, and 

 when so obtained was found capable of acting with con- 

 siderable energy on pyrogallol and hydroquinone, but to 

 have no effect on tyrosin ; it contained therefore only 

 laccase. 



The precipitate was washed with 200 cc. of chloroform 

 water and when it was well swollen up, forming a semi- 



