76 
Miss Durham ( 155 ) found that after filtering off the pigment pro- 
duced by their action upon tyrosin, the preparations of animal tyro- 
sinase could act upon fresh portions of tyrosin. According to Ber- 
trand ( 59 ) tyrosinase is more easily destroyed by heat than laccase ; 
thus he found the former to be destroyed in twelve minutes at 
60-70° C., whereas laccase withstood this temperature for twenty 
hours. Gessard ( 182 ) found tyrosinase to be almost destroyed by 
heating to 65° C. for thirty seconds. Chodat and Staub ( 117 ) observed 
the activity of tyrosinase to increase with a rise of temperature to 
61° C., and to become inactive at 61° C. Advantage has been taken 
of this difference in the stability of tyrosinase and laccase toward 
heat in the separation of the two enzymes, and tends to show that 
these two oxidases are different ferments. Thus Russula delica con- 
tains both tyrosinase and laccase. If now, according to Bertrand ( 54 ) 
the fungus be macerated with its own weight of chloroform water and 
the liquid thus obtained be treated with alcohol in the proportion of 
three volumes of alcohol to two volumes of extract, a precipitate is 
obtained which gives the reactions of tyrosinase. If now the filtrate 
be evaporated at 50° C. to one-tenth of its original volume, it will be 
found to act energetically on hydroquinone and pyrogallol, but to be 
without action on tyrosin. In other words, the filtrate that has been 
subjected to a temperature of 50° C. for some time still contains 
laccase, but no tyrosinase. Similarly Bach ( 25 ) has obtained laccase 
free from tyrosinase from the fungus Lactarius vellereus by heating 
to 75° C. Miss Willcock ( 451 ) has shown that tyrosinase is not killed 
by the radium emanation. 
Kastle has observed that glycerin extracts of Lactarius piperatus 
and Lactarius volumen oxidize tyrosin strongly after having been 
kept four years in glass-stoppered bottles under ordinary laboratory 
conditions. 
Like many other enzymes, tyrosinase is sensitive to the action of 
acids, alkalies, salts, and certain poisons like hydrocyanic acid. 
Thus Wolff ( 459 ) finds that the tyrosinase from Russula delica is most 
active on tyrosin when the solutions are neutral to phenolphthalein. 
Similarly Abderhalden and Guggenheim (*) find that N/100 hydro- 
chloric acid inhibits the action of tyrosinase, and that N/100 sodium 
hydroxide retards it considerably. After treatment with acid or 
alkali, neutralization of the acid or alkali fails to restore it to its 
original activity, indicating that the ferment is actually destroyed 
under these conditions. Gessard ( 182 ) found that while salts of the 
metals promote the coagulation of the black pigment, they hinder 
the development of the initial coloration, the retardation being pro- 
portional to the quantity of salt present. Neutral salts were found 
to produce a retardation ranging from twenty-three minutes to nine 
days, and alkaline carbonates prevented the development of the ' 
