Chemistry of Coat-Colour in Animals. 



51 



from recessive white mice, which were tested with an active tyrosinase 

 procured from black mice of the same age, as well as with that from black 

 rabbits. These extracts behaved in every way like those from the recessive 

 white rabbits. The method of preparing the extracts was similar to that 

 already described, except that the mice, on account of their relative 

 immaturity at birth, were kept till they were more than a week old, and 

 their skins were chopped with a knife instead of being passed through a 

 machine. 



Before ascertaining the absence of tyrosinase in recessive whites, it was 

 necessary first to show experimentally what has already been concluded 

 logically, namely, that no tyrosinase inhibitor can be present in recessive 

 whites. This was clearly shown to be the case by the following experiment. 



2. Distribution of Tyrosinase. 



Experiment V : The Absence of a Tyrosinase- Inhibitor in Recessive White 

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

 from black rabbits was added to each tube. 







Appearance after 12 hours. 



No. 



Substances added. 











Without H 2 2 . 



With H 2 2 . 



1 







+ + 



2 



Tyrosine + 2 c.c. of the extract from recessive 













+ 



3 







+ 



4 



^-cresol + 4 c.c. extract from recessive white 











+ 



+ 



+ + indicates strong reaction. 

 + indicates positive reaction. 

 — indicates no change. 



As much as 50 per cent, of the extract from recessive whites was powerless 

 to prevent darkening, though as little as 20 per cent, of the extract from 

 English rabbits was sufficient to inhibit the reaction completely. 



No. 3 was prepared as a control by substituting normal saline for the 

 recessive white extract, in order to indicate the effect of dilution upon the 

 ferment fluid. 



The absence of an inhibitor was confirmed by using the more delicate 

 reagent p-cresol in a solution of ferment diluted with two volumes of 

 recessive white extract, and also by testing the precipitates formed by 

 saturation with ammonium sulphate and by the addition of an excess of 



