50 



Mr. H. Onslow. 



there among the blue granules, as if now and then one of them had become 

 oxidised. In other hairs, such as those of white mice, the medullary cells 

 appeared bright blue and entirely devoid of granules. Whether or not 

 these bodies represent an unoxidised chromogen there is not sufficient 

 evidence to say. Their presence or absence was not correlated either to 

 dominant or recessive whiteness, but their occurrence seemed rather to 

 be specific in nature, as may be seen from the following Table: — 



White hairs containing granular 

 bodies. 



White hairs lacking granular 

 bodies. 



Albino rabbit. 



Dutch rabbit. 



Angora rabbit. 



English rabbit. 



Himalayan rabbit. 



Agouti rabbit (belly). 



Mountain hare (winter coat). 



White cat. 



Border terrier 



White foxhound. 



Tricolor foxhound. 



Arctic fox (winter coat). 



Albino mouse. 

 Piebald mouse. 

 Mus sylvaticus (belly). 

 Piebald rat. 

 Agouti rat (belly). 

 Bed squirrel (belly). 

 Ermine (winter coat). 

 Albino guinea-pig. 

 Piebald guinea-pig. 

 White sheep. 



White hairs from a white horse, a white goat, a white Pomeranian, and 

 an albino wolf were also examined. It was very difficult to determine 

 whether they contained any granules, for although a number of particles 

 were plainly visible within the medulla, they did not group themselves in the 

 form of pigment granules, and their shape and distribution were irregular. 



VI. The Absence of Tvkosinase-Inhibitor and of Tyrosinase in the 

 Skins of Eecessive White Rabbits and Mice. 



1. Materials and Methods. 



Owing to some difficulty in obtaining albino and black rabbits simul- 

 taneously, preliminary experiments were made upon a variety of rabbits 

 known as Black Dutch. These rabbits have the hindquarters pigmented 

 and the forequarters white, patches of pigment on the head and ears, and 

 pigmented eyes. The special convenience of such half-black, half -white 

 animals was that the black portions of the skin, when removed from the 

 white, could be used to procure an active tyrosinase with which to test for 

 the presence of an inhibitor in the white portions. Eecessive white rabbits - 

 with pink eyes were also tested on several occasions to make sure that 

 absence of colour was caused, in their case as well as in that of the piebalds, 

 by the lack of tyrosinase. Further, experiments were made with extracts 



