The vibrations which this sense undergoes, from the odoriferous particles, are communicated to the brain, which acting, in its turn, upon the nerves, the animal is stimulated to open its mouth, to obtain that sustenance of which it feels the want. The sense of appetite being less acute in man than in brutes, the infant at its birth feels only the desire of receiving nourishment, which it announces by its cries, but it cannot obtain it of itself; it receives no information from the smell, and is obliged to have its mouth put to the nipple, when the agitations, excited by the touch and smell, are communicated to the brain and nerves, and the child makes the necessary motions for sucking in its nourishment. Solely by the smell and taste, the senses of appetite, can the animal be informed of the presence of its food, and of the place where it is, as its eyes are still closed, and would, even if they were open, in no degree contribute towards the determination of motion. Vision has a greater relation to knowledge than to appetite, and in man the eye is open from the moment of his birth; in most animals it is shut for several days, but in whom the senses of appetite are far more expanded, and more perfect. The same remark is alike applicable to progressive motion, and to all the other exterior movements. A new-born infant can hardly move its members, and it is a long time before it attains strength sufficient to change its place, but in a very little time does a young animal acquire these faculties. In the animal these powers relate solely to the appetite, which is vehement, quickly developed, and the sole principle of motion; in man the appetite is weak, more slowly developed, and can have less influence than knowledge upon the determination of motion; man is necessarily, in this respect, more backward than the animal.