Chemistry of Coat-Colour in Animals. 



47 



plant juices. Lastly, Gortner* claims to have modified the pigmentation of 

 the larvae of Spelerpes bilineatus, by subjecting the eggs to a dilute solution 

 of orcin, and to have increased the pigmentation by subjecting them to a 

 dilute solution of tyrosine. Moreover, the Mendelian explanation of 

 dominant whiteness, involving the existence of a factor which inhibits 

 pigment-formation, even in the presence of the full pigment-producing 

 mechanism, is sufficiently convincing to give great support to the chemical 

 evidence available. 



IV. The Tyrosinase-Inhibitoe. 



1. The Presence of the Inhibitor in the Skins of English Rabbits. 



Experiment IV: The Effect of the Inhibitor in English Rabbit Skins. — 

 2 c.c. of the ferment fluid (prepared as previously, see pp. 40 and 41), tyrosine, 

 and hydrogen peroxide were added to each tube. 



No. 



Substance added. 



Appearance after 

 12 hours. 



1 





+ 



2 







3 



] c.c. English extract (boiled) 



+ 



4 



Precipitate obtained from half saturation of 1 c.c. English extract 









+ 



5 







6 



Precipitate obtained from full saturation of 1 c.c. English extract 











7 



Filtrate from precipitate in No. 6 



+ 



+ indicates positive reaction. 

 — indicates no change. 



The English extract alone had no action on tyrosine, either before or after 

 the addition of hydrogen peroxide. 



As little as 20 per cent, of the English extract was found to be sufficient 

 completely to inhibit the oxidation due to the tyrosinase. 



It is seen that the inhibitor cannot be precipitated by half saturation with 

 ammonium sulphate, but that it can be precipitated by full saturation. 



In Nos. 4 and 6 the precipitate was dissolved in the same volume of water 

 as that of the extract taken. 



The fact that ammonium sulphate alone is not the cause of the inhibition 

 is shown by the result of No. 7. 



Attempts further to purify the inhibitor obtained from the ammonium 

 sulphate precipitate have so far failed. The chief cause of this is the inherent 



* Gortner, 'Ohio Nat.,' vol. 13, No. 3, p. 49 (1913). 



