There are some persons who are of opinion that the fineness of the wit does not depend upon the thinness of the blood, but that animals are more or less stupid in proportion to the skin or other coverings of the body, as the oyster and the tortoise, for instance: that the hide of the ox and the bristles of the hog, in fact, offer a resistance to the fine and penetrating powers of the air, and leave no passage for its transmission in a pure and liquid state. The same, they say, is the case, too, with men, when the skin is very thick or callous, and so excludes the air. Just as if, indeed, the crocodile was not equally remarkable for the hardness of its skin and its extreme cunning.