46 



Mr. H. Onslow. 



experiments the percentage yield from the dominant and the recessive whites 

 was so similar, Gortner concluded that dominant whites do not possess a 

 "white melanin" which is lacking in recessive whites; and, further, that 

 the greyish brown substance derived from the feathers was not a pigment 

 body at all, but merely a decomposition product of the keratin. The mere 

 fact that the percentage of the grey substance was no larger in the dominant 

 than in the recessive white feathers does not seem in itself to be a very 

 strong argument in favour of the absence of the white piginent body. If this 

 existed it might easily have been hydrolysed by the strong alkali used 

 (10 per cent). 



But Gortner is undoubtedly correct in denying the pigment nature of the 

 greyish brown substance. I have obtained it by Spiegler's methods from 

 the hair of albino rabbits and white sheep, and find it to be an admixture of 

 cholesterine and cholesterine esters from the surface of the hair and a 

 substance resembling meta-protein derived from the hydrolysis of the 

 keratin. The properties of this substance will be dealt with in a separate 

 communication. 



2. The Inhibitor Theory. 



Having discarded the theory of a " white melanin," Gortner* suggested that 

 an inhibitor might be present. He assumed that normal pigment formation 

 is due to the oxidation of a chromogen (tyrosine) induced by the action of an 

 enzyme (tyrosinase), and suggested that the tyrosine gives rise to (or is 

 replaced by) a closely related substance which acts as an inhibitor or anti- 

 tyrosinase. This substance is deposited in the epithelial cells of the skin, 

 and the potentiality to reproduce it is transmitted to all the offspring. In 

 support of this theory he was able to show that certain dihydroxyphenols 

 which carry the hydroxyl groups in the meta-position to each other, such as 

 orcin and phloroglucin, inhibit the action of certain tyrosinases upon tyrosine 

 and other compounds. Later, Keeble and Armstrong^ were of the opinion 

 that the dominant white variety of P. sinensis contains an inhibitor, after the 

 destruction of which by hydrogen cyanide the petals give strong oxidase 

 reactions with suitable reagents. Miss Wheldale* also regards the pale 

 shades of certain flowers which are dominant over the deeper shades as due 

 to the presence in the petals of deoxidising substances such as tannin or 

 sugar, and Atkins§ has observed and precipitated anti-oxidases in numerous 



* Gortner, 'Jour. Biol. Chemistry,' vol. 10, No. 2, p. 113 (1911). 



t Keeble and Armstrong, ' Journal of Genetics, 1 vol. 2, p. 277, No. 3 (November, 1912). 



\ Wheldale, 'Progressus Rei Botanicre,' vol. 3, p. 457 (1910). 



§ Atkins, ' Sci. Proc. Roy. Dublin Soc.,' vol. 14, Nos. 7 and 8 (1913). 



