70 University of California Publications in Zoology [Vol. 11 



tested with Million's reagent. Owing to the fact that the tyro- 

 sinase when i.solated by precipitation with alcohol or other agents, 

 is much less powerful than the original extract, in most of these 

 experiments no attempt was made to isolate the oxidase. Kastle 

 (1910, p. 63) has experienced the same difficulty and says, 

 "Inasmuch as we have no criterion for judging of the absolute 

 purity of a ferment, it is very doubtful whether much is gained 

 by the attempt to i.solate laccase and the other oxidases in pure 

 condition. ' ' 



Two series of experiments were made. In the first, the various 

 foods under investigation were cooked and ground and then 

 added to solutions of tyrosin and tyrosinase; in the second the 

 foods were digested in pancreatin and pepsin and the filtrates 

 used. 



Series A. Undigested Foods 



For these experiments 0.2 gm. of the food was weighed out 

 after it had been thoroughly cooked by boiling. This portion was 

 ground in a glass mortar with 10 ec. of distilled water and added 

 to the tyrosinase solution with or without tyrosin. The results 

 are more or less variable, but certain facts may be stated with 

 assurance to hold for all sorts of tyrosinase used. 



Albumen inhibits the action of the tyrosinase the least of 

 any of the foods. Yolk and liver inhibit the reaction more than 

 albumen — liver usually inhibiting more than yolk. Liver allowed 

 to spoil and then cooked inhibits the reaction completely, giving 

 a white precipitate and a clear, colorless liquid. Liver that has 

 been kept for several days, but cooked from time to time to 

 prevent its putrefaction, inhibits the reaction less than does the 

 fresh liver. Fresh and stale eggs inhibit the reaction equally. 

 Lecithin* inhibits the action of the tyrosinase markedly — the 

 color appearing slowly and only toward the surface of the liquid. 



* Lecithin was prepared as follows : Yolks of hen 's eggs were washed in 

 water without breaking the membrane. An equal volume of 10 per cent 

 sodium chloride solution was added and the mixture extracted in a separ- 

 atory funnel with two volumes of ether. To the ether fraction was added 

 an equal volume of acetone. The precipitated lecithin was dried in a 

 sulphuric acid dessicator. 



