54 



Mr. H. Onslow. 



in the fluid extract, which has no effect upon mono-phenols, but which 

 readily oxidises the more complex phenols. 



Now the extract was observed to be very thermostable, and this made it 

 doubtful whether a true enzyme were present. Bertrand* has, however, 

 described a laccase capable of oxidising phenols, but with no action on 

 tyrosine, which could be subjected to a temperature of 70° C. for 15 minutes 

 without losing its activity. Moreover, Gortnerf has described a similar 

 enzyme which he separated from tyrosinase by bringing the mixture to 

 boiling point, at which temperature the tyrosinase is destroyed and an active 

 enzyme remains which oxidises quinol. " This oxidase," he adds, " is much 

 more resistant to heat than tyrosinase, and may be heated at 100° C. for 

 some minutes without losing much , of its activity. Prolonged heating, 

 however, gradually causes it to lose its oxidising power." This enzyme was 

 obtained from meal-worms, but a similar one was also extracted from the 

 tissues of various vertebrates, and notably from the skin of albino rats. 



In order to test the effect of temperature on my skin extracts the following 

 experiment was made with recessive white rabbits. 



Experiment IX: The Effect of Temperature on the Oxidation of Phloro- 

 glucin by the Recessive White Extract. — The recessive white extract (prepared 

 as previously) was added to each tube, as well as phloroglucin. 



In each case the extract was heated for a period of 10 minutes at the 

 temperature stated. Before heating, the fluid was as usual made faintly 

 alkaline to litmus, so that little or no coagulation took place. 



No. 



Temperature. 



Appearance after 

 12 hours. 



1 



37° C. 



+ 



2 



78 



+ + 



3 



82 



+ + 



4 



90 



+ 



+ + indicates strong reaction. 

 + indicates positive reaction. 

 — indicates no change. 



The increase in the oxidation of Nos. 2 and 3 after a slight heating agrees 

 with Gortner's statement that <: long-continued boiling causes a gradual 

 loss in the oxidising power, although a very short heating seems to increase 

 the activity." In view of this great resistance to heat it seems extremely 

 doubtful whether an enzyme, as generally understood, can be responsible for 



* Bertrand, < Paris, C.E. Acad. Sci.,' vol. 123, p. 463 (1896). 

 t Gortner, 'Trans. Chem. Soc.,' vol. 97, p. 110 (1910). , 



