9.] [Footnote 59: In the _Medico-Chirurgical Transactions_, vol.liii.
(1870), Dr.Ogle has adduced some curious physiological facts bearing on the presence or absence of white colours in the higher animals.

He states that a dark pigment in the olfactory region of the nostrils is essential to perfect smell, and that this pigment is rarely deficient except when the whole animal is pure white, and the creature is then almost without smell or taste.

He observes that there is no proof that, in any of the cases given above, the black animals actually eat the poisonous root or plant; and that the facts are readily understood if the senses of smell and taste are dependent on a pigment which is absent in the white animals, who therefore eat what those gifted with normal senses avoid.

This explanation however hardly seems to cover the facts.
We cannot suppose that almost all the sheep in the world (which are mostly white) are without smell or taste.

The cutaneous disease on the white patches of hair on horses, the special liability of white terriers to distemper, of white chickens to the gapes, and of silkworms which produce yellow silk to the fungus, are not explained by it.