These aberrations of animal sensibility then exist entirely in the brain; it is an irregularity, a derangement of perception; this irregularity presents phenomena analogous to the following; we often refer to the skin a sensation of heat, as we shall see, though caloric is not disengaged there in a greater quantity than usual. We know that oftentimes the sensations of hunger and that of thirst are purely sympathetic, and that the cause which produces them in a natural state does not then exist in the stomach or intestines. We know the illusions of vision, of hearing, of the smell even, &c. We have not studied sufficiently the irregularities of perception; those of the memory, the imagination, the judgment, &c. have been analysed. These, however, have been almost forgotten. They perform the greatest part in animal sensibility. 2d. Animal contractility supposes constantly nervous action, when it is put in exercise sympathetically. In fact we shall see that this property cannot be exerted without the triple action of the brain, of the nerves that go to the muscles that move, and of the muscles themselves. When a muscle of animal life is brought into action by the irritation of any distant organ, by the distension of the ligaments of the foot for example, this organ acts at first upon the brain, which then reacts by means of the nerves upon the voluntary muscles that are concerned in convulsions. The following is an experiment by which I satisfied myself of the cerebral and nervous influence in the sympathies that occupy us. I cut all the nerves of the inferior limb of one side, in different animals, and I afterwards irritated in a thousand different ways, very irritable parts, as the retina, the pituitary membrane, the marrow of the bones, &c. I produced in this way a number of sympathetic phenomena, sometimes of organic contractility, as vomiting, involuntary evacuations of urine, fecal matter, &c. sometimes of animal contractility in the muscles whose nerves remained untouched. But the muscles whose nerves were cut, were never brought into action. I have very frequently repeated these experiments, which would have certainly produced results, if the nervous communications could, without the intervention of the brain, make the muscles of animal life contract. I would observe upon this subject, that sufficient regard has not been paid in experiments upon sensibility, to the sympathetic phenomena. I do not know even that these phenomena have been the object of any experiments upon animals, before those of which I have here given the first results, and which I propose to multiply under other points of view. There are then two things in all sympathy of animal contractility, viz. 1st, the action upon the brain of the organ that suffers, by means, of which as yet we know but little; 2d, reaction of the brain upon the voluntary muscles. In this last period of sympathy, the nerves of animal life are the agents constantly necessary.