3G 



A Contribution to our Knowledge of the Chemistry of Coat-Colour 

 in Animals and of Dominant and Recessive Whiteness. ' 

 By H. Onslow. 



(Communicated by Prof. F. G. Hopkins, F.R.S. Received January 30, 1915.) 



CONTENTS. 



PAGE 



I. — Introduction '. 36 



II. — The Mechanism of the Action of Tyrosinase in Coloured Animals 38 



1. Miss Durham's Experiments. 



2. The Peroxidase Present in the Skins of Coloured Rabbits and Mice. 



(«) Material. 



(b) Methods 



(c) Properties. 



(d) Distribution and Nature of the Oxidase in Rabbits of 



Different Colours. 



III. — The Cause of Dominant Whiteness 44 



1. The " White Melanin " Theory. 



2. The Inhibitor Theory. 



IV. — The Tyrosinase-Inhibitor 47 



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



2. Distribution of the Inhibitor in the Skins of Agouti and Yellow 



Rabbits. 



V. — The Cause of Recessive Whiteness 48 



1. The Distribution of Enzyme and Chromogen. 



2. On the Presence of Granules in certain White Hairs, and the 

 Possibility of their Chromogenic Nature. 

 VI. — The Absence of Tyrosinase-Inhibitor and of Tyrosinase in the Skins of 



Recessive White Rabbits and Mice 50 



1. Material and Methods. 



2. Distribution of Tyrosinase. 



3. The Effect upon the Skin Extracts of Dihydroxyphenols. 



VII. — A Possible Cause of Colour Variation 55 



VIII. — Summary and Conclusions 57 



I. Introduction, 



Our knowledge of the pigments which give rise to the coat-colour of animals 

 is very limited, and is chiefly confined to work on the melanins, an extensive 

 bibliography of which is to be found in a monograph by Robert* and also in a 

 paper by von Fiirth.-j- The dark bodies which remain as a cleavage residue 

 after the acid hydrolysis of proteins are sometimes also called melanins, as 

 well as the artificial products formed by the action of tyrosinase upon tyrosine. 



* Robert, 'Wiener Klinik,' vol. 27, No. 4 (1901). 



t Von Eiirth, ' Centralbl. fur allg. Path, und pathol. Anat.,' vol. 15, p. 617 (1904). 



