Some very curious physiological facts bearing upon the presence or
absence of white colors in the higher animals have lately been adduced
by Dr. Ogle. It has been found that a colored or dark pigment in the
olfactory region of the nostrils is essential to perfect smell, and
this pigment is rarely deficient except when the whole animal is pure
white. In these cases the creature is almost without smell or taste.
This, Dr. Ogle believes, explains the curious case of the pigs in
Virginia adduced by Mr. Darwin, white pigs being poisoned by a
poisonous root which does not affect black pigs. Mr. Darwin imputed
this to a constitutional difference accompanying the dark color, which
rendered what was poisonous to the white colored animals quite
innocuous to the black. Dr. Ogle, however, observes that there is no
proof that the black pigs eat the root, and he believes the more
probable explanation to be that it is distasteful to them, while the
white pigs, being deficient in smell and taste, eat it, and are
killed. Analogous facts occur in several distinct families. White
sheep are killed in the Tarentino by eating _hypericum criscum_, while
black sheep escape; white rhinoceros are said to perish from eating
_euphorbia candelabrum_; and white horses are said to suffer from
poisonous food where colored ones escape. Now it is very improbable
that a constitutional immunity from poisoning by so many distinct
plants should, in the case of such widely different animals, be always
correlated with the same difference of color; but the facts are
readily understood if the senses of smell and taste are dependent on
the presence of a pigment which is deficient in wholly white animals.
The explanation has, however, been carried a step further by
experiments showing that the absorption of odors by dead matter, such
as clothing, is greatly affected by color, black being the most
powerful absorbent, then blue, red, yellow, and lastly white. We have
here a physical cause for the sense-inferiority of totally white
animals which may account for their rarity in nature. For few, if any,
wild animals are wholly white. The head, the face, or at least the
muzzle or the nose, are generally black. The ears and eyes are also
often black; and there is reason to believe that dark pigment is
essential to good hearing, as it certainly is to perfect vision. We
can therefore understand why white cats with blue eyes are so often
deaf--a peculiarity we notice more readily than their deficiency of
smell or taste.--_Dr. Wallace, British Association_, 1876.
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