Besides it is difficult to decide the question by ocular observation. The delicacy of these elongations conceals their structure, even from our microscopical instruments, agents from which anatomy and physiology do not appear to me to have derived much assistance, because when we see obscurely, each sees in his own way and according to his own wishes. It is then the observation of vital properties that should especially guide us; now, it is evident to judge by them, that the villi have the nature I have attributed to them. The following experiment served to demonstrate to me the influence of the papillary body upon the cutaneous sensibility; it succeeds also upon the mucous membranes. Remove the epidermis in any part and irritate the papillary body with a sharp stilet; the animal is agitated, cries out and gives marks of acute pain. Slide afterwards, through a small opening made in the skin, a pointed stilet into the sub-cutaneous cellular texture, and irritate the internal surface of the corion; the animal remains quiet and makes no noise, unless some nervous filaments accidentally struck make him suffer. Hence it follows very evidently, that it is upon the external surface of the skin that its sensibility resides, that the nerves pass through the corion without contributing to its texture, and that their expansion takes place on the papillary body. It is precisely so with the mucous surfaces. Observe that this circumstance coincides very well with the functions of the two surfaces, which receive by their free portion the action of external bodies, to which they are foreign by their adhering portion. The papillæ exhibit very great varieties. On the tongue, in the small intestines, in the stomach and in the gall-bladder, they are remarkable for their length. The œsophagus, the large intestines, the bladder, all the excretory ducts have those that are less evident; these last especially and the urethra in particular, are almost smooth in their whole mucous surface. We can scarcely distinguish the papillæ in the frontal, sphenoidal, maxillary sinuses, &c. These small nervous eminences are sufficiently distinct and separate upon the tongue. In the nasal fossæ, the stomach and the intestines, they are so near together and at the same time so delicate, that the membrane has at first view an uniform and smooth appearance, though it is covered with these elongations. Each papilla is simple; no bifurcation is ever observed at its extremity. All appear to have a pyramidal form, if we can judge at least by those which are the most evident.