Chemistry of Coat-Colour in Animals. 



49 



namely, the enzyme and the chromogen. Gortner* has shown that in the 

 case of the Colorado Potato-beetle, the colour pattern of the elytron is due 

 to a restriction of the chromogen to the coloured areas, and that the enzyme 

 is secreted over the entire surface. This distribution of chromogen was 

 made evident by the fact that the pigmentation did not become general 

 when an unpigmented elytron was placed in a solution of tyrosinase, 

 whereas a solution of tyrosine caused the elytron to become pigmented 

 over its entire surface. But in the case of rabbits the distribution is, as 

 will be shown, different, the tyrosinase being restricted to the pigmented 

 areas, and entirely absent from the white areas. It was easy to demonstrate 

 the absence of a tyrosinase, but it was not so simple to do this in the case 

 of a chromogen, owing to the difficulty attending its extraction. An attempt 

 was therefore made, by means of a microscopical examination of a number 

 of white hairs, to discover whether an unoxidised chromogen was present in 

 any of them. 



2. On the Presence of Granules in Certain Wliite Hairs, and the Possibility 

 of their Chromogenic Nature. 



It was observed that the medullary cells of some white hairsf contained 

 groups of small granular bodies, which may be the same as the small, 

 conspicuously stained bodies in colourless hair, described by Nathusius,; 

 and believed by him to be structurally related to pigment granules. They 

 could be stained with hot aqueous solutions of methyl green or methyl 

 violet, bat these stains were not permanent. Much better results were 

 obtained by using Nissl's methylene blue diluted with four volumes of 

 water. The hairs were placed in this solution and heated in a water-bath 

 for 30-60 minutes, according to the coarseness of the hairs, after which 

 they were allowed to remain in xylol for about an hour, in order to 

 expel the air from the vacuoles and to remove the excess of stain. With 

 fine hairs, such as mouse hairs, it was found necessary to dilute the stain 

 twenty times to prevent the medullary cells from becoming stained too 

 deeply. Treated in this manner the granular bodies appeared exactly 

 like groups of bright blue pigment granules. They were about the same 

 size (l"5/i) as normal granules, and were situated in groups of the same 

 appearance and in the same position within the medullary cells. In the case 

 of white hairs from the belly of wild rabbits, in which a little pigment is 

 present, normal black pigment granules were found interspersed here and 



* Gortner, 'Arner. Nat.,' vol. 45, p. 743 (December, 1911). 

 t Onslow, 'Knowledge,' New Series, vol. 11, Part V, p. 161 (May, 1914). 

 I Nathusius, ' Archiv fur mikroskop. Anat.,' vol. 43, pp. 152, 153 (1894). 

 VOL. LXX'XIX. — B. E 



