In these animals also the mucus covering the olfactory area of the nose is itself pigmented.
We have seen that human albinos are anosmic, and the same is probably true of animal albinos. But care is necessary in making observations on suspected albinos in animals, as even when they are altogether white a certain amount of black pigment remains about the face and nose.
The following reports, however, would lead us to conclude that as with man, so with the animals, a relative deficiency of pigment is associated with a dull olfactory sense.
It is by smell that the herbivora detect and avoid plants which are poisonous, and when poisoning does occur, it is usually a white animal that suffers. In some parts of Virginia the farmers will only rear black pigs, because, they say, the white ones eat and are poisoned by the roots of Lachtanthus tinctoria. For the same reason in the Tarentino only black sheep are reared.
Thirdly, the dark-skinned human races have a keener sense of smell than the lighter races.
Fourthly, the sense grows more acute as we get older, as we have already seen, and nasal pigmentation, it is said, also increases with age.
As to the function of the olfactory pigment, Ogle remarks first of all that odours are absorbed more readily by dark than by light materials.
Pigment is also present in the labyrinth of the
