Chemistry of Coat-Colour in Animals. 



53 



T>1 1 A 1 A 

 JTIlCHOl aGCleCl. 



Appearance after 12 hours. 



Without H 2 2 . 



With Hj0 3 . 



None 





+ + ' 



Phloroglucin 



+ + 



+ 





+ 



+ 





+ 



+ 



Phenol 







+ + indicates strong reaction. 

 + indicates positive reaction. 

 — indicates no change. 



In every case in which a di-phenol was added, the ring that appeared 

 after 12 hours was coloured more or less deeply yellow. This result 

 suggested either that tyrosinase oxidises these di-phenols yellow, or that the 

 di-phenols inhibit tyrosinase, and are themseves acted upon by a specific 

 ferment or some other agent present in the solution. To prove that the 

 oxidation was not due to tyrosinase, the skin extracts from both dominant 

 and recessive white rabbits were tested with phloroglucin, etc., and in both 

 cases the results were similar to those given by the coloured skins, as is 

 shown by the following experiment. 



Experiment VIII : The Effect of the Extracts from Dominant and Recessive 

 White Rabbits upon Dihydroxyphenols. — The extracts were prepared as before, 

 and to each tube was added the phenol to be tested. 



Extract. 



Phenol added. 



Appearance after 

 12 hours. 



Black rabbits 



Recessive white rabbits 

 English rabbits 



?> jj • " 



» ? i j> •■■ ■ 



Recessive white rabbits 



Phloroglucin 



jj 



Orcin 



Resorcin 



Hydroquinone (reaction neutral) 



Pyrogallol (reaction neutral) 



Phenol 



+ 

 + 



+ 

 + 

 + 



+ + 

 + + 



+ indicates a yellow ring. 

 + + indicates a brown ring. 

 — indicates no change. 



The fact that the recessive white extract, containing no tyrosinase, behaves 

 in a way similar to that from black rabbits, proves that the effect on phloro- 

 glucin cannot be attributed to a tyrosinase. The reaction must be due, 

 therefore, either to an enzyme which is specific for poly-phenols, but which 

 has no action on tyrosine, or else to the presence of organic colloidal material 



