56 



Mr. H. Onslow. 



sight to be opposed to this view. When, however, purified samples of the 

 pigment were used, I was quite unable to detect any such difference. 



In order to put this hypothesis to a further test, a rougli experiment was 

 devised as follows : — A few decigrams of pigment were prepared from black, 

 chocolate, and yellow rabbits, by treating the hair according to Gortner's* 

 method of extracting melanin, with a 0'2-per-cent. sodium hydroxide 

 solution. The three amorphous black preparations resulting appeared 

 identical, and their solubilities were found to be similar, that is to say, 

 they were easily soluble in alkalies, slightly less soluble in dilute acids 

 (N/20 HC1) and insoluble in strong acids and saturated ammonium sulphate 

 solution ; 10 mgrm. of each of the purified preparations were then dissolved 

 in 10 c.c. of 5-per-cent. sodium hydroxide, and the solutions compared in a 

 Dubosq colorimeter. To the eye these solutions appeared a fairly uniform 

 yellow colour, and colorimetrically the average difference between yellow 

 and chocolate and between chocolate and black was not more than 18 per 

 cent. This difference can be partly accounted for by the slight variation 

 in the colour of the solutions and the consequent difficulty of comparison, 

 and partly by the admittedly unsatisfactory method of extracting the 

 pigment. The similarity in the colour of the solutions is the more striking 

 in view of the contrast in the appearance of bright yellow and of black 

 rabbits, a difference which cannot be less than several hundred per cent. 

 On the other hand, it is conceivable that during extraction the yellow and 

 chocolate pigments may have been decomposed by the dilute alkali and 

 converted into black pigment. 



There is one other class of colours among rabbits which deserves attention, 

 namely, the so-called dilute colours, such as blue, which is the dilute form 

 of black. The pigment which gives rise to this colour is identical in 

 appearance with that of the black rabbit, both microscopically and in 

 solution. The tyrosinase which it is possible to extract also behaves like 

 that of the black rabbits. To account for this difference in colour it has 

 been suggested that the pigment granules are deposited far less abundantly 

 in the blue hair than in the black.f A number of careful microscopical 

 examinations have, however, convinced me that the amount of pigment 

 deposited in the distal portion of the hairs is not appreciably less in blue 

 and other dilute animals than it is in black.} The basal portions, on the 

 other hand, contain very few granules, but the colour of an animal is given 

 by the distal portion of the hair alone, since this is the only part of the 



* Gortner, ' Jour. Biol. Chemistry,' vol. 8, No. 4, p. 342 (1910). 



t Bateson, ' Mendel's Principles of Heredity,' p. 83. 



I Onslow, ' Knowledge,' New Series, vol. 11, Part V, p. 161 (May, 1914). 



