It is evident, therefore, that in brutes the interior sense differs in nothing from the exterior but in the property of retaining the impressions it has received, a property by which alone all the actions of animals may be explained, and some idea obtained of what passes within them; a property which likewise demonstrates the essential and infinite difference which subsists between them and us, and from which may be distinguished in what respects they are similar. The degrees of excellence in the senses do not follow the same order in the brute as in the human species. The sense which has the strongest affinity to thought, is the touch. This is enjoyed by man in greater perfection than by animals. That which has the strongest affinity to instinct and appetite, is that of smelling; a sense in which man must acknowledge an infinite inferiority. Man, then, has the greatest tendency to knowledge, and the brute to appetite. In the former, the sense first in point of excellence, is the touch, and smelling the last; and this difference corresponds with the nature of each. The sense of seeing is at best uncertain, without the aid of the touch, and therefore less capable of perfection in the brute than in man. The ear, though perhaps as perfect in the former as in the latter, is of much less use to the animal, from the want of speech, which in man is an appendage to the sense of hearing, an organ of communication which renders it an active sense; whereas in the other hearing is a sense almost entirely passive. Man, then, enjoys the senses of feeling, seeing, and hearing, more perfect, and the sense of smelling more imperfectly than other animals; and as the taste is an inferior smell, and has also a stronger relation to appetite than any of the other senses, there is a sufficient probability to suppose that animals enjoy it in a more exquisite degree than man. Of this a proof might be adduced from the repugnance which animals have to certain kinds of food, and from their natural appetite for such as are proper for them; while man, unless informed of the difference, would eat the fruit of one tree for that of another, and even hemlock for parsley. The excellence of the senses proceeds from Nature; but art and habit may render them still more perfect. A painter sees, at the first glance, numbers of shades and differences, which another person will pass over unnoticed. A musician, always habituated to harmony, receives a lively sensation of pain from discord. In like manner are the senses, and even appetites of animals rendered more perfect. Birds may be taught to repeat words, and imitate tunes; and the ardour of a dog for the chace may be increased by accustoming him to a certain reward.