All sanguineous animals, then, have skin; but not all such animals
have hair, save only under the circumstances described above. The hair
changes its colour as animals grow old, and in man it turns white or
grey. With animals, in general, the change takes place, but not very
obviously, or not so obviously as in the case of the horse. Hair turns
grey from the point backwards to the roots. But, in the majority of
cases, grey hairs are white from the beginning; and this is a proof
that greyness of hair does not, as some believe to be the case,
imply withering or decrepitude, for no part is brought into
existence in a withered or decrepit condition.