31. However, it is difficult to decide the question by ocular observation; the tenuity of these prolongations conceals their structure even from our microscopic instruments, a kind of agents by which physiology and anatomy do not appear to me in other respects ever to have obtained great assistance, because when parts are so viewed each person sees in his own way, and is impressed accordingly. It is therefore the observing of the vital functions that should above all guide us. Now by judging of the villosities in this way it appears evident, that they have the nature which I have attributed to them. The following experiment will serve to demonstrate the influence of the corps papillaire upon the cutaneous sensibility: it succeeds also with mucous membranes. If we remove any part of the epidermis, and irritate the corps papillaire with a pointed instrument, the animal writhes, cries, and gives signs of acute pain. If afterwards the cutis be pierced, and with the instrument the internal surface of the chorion be irritated, the animal will not appear to suffer pain, unless by accident some nervous filaments should be touched. Thence it follows very evidently, that the sensibility of the skin resides in its external surface, that the nerves pass through the chorion without being interwoven with its texture, and that their diffusion only takes place on the corps papillaire. It is the same in mucous surfaces. 32. The length and form of the villosities vary in the different mucous surfaces. Their appearance is not the same in the stomach, the intestines, the bladder, the gall bladder, on the glans, &c.; which variation exactly coincides with the sensibility peculiar to each organ, a sensibility proved by numerous observations since Bordeu, who was the first to direct the attention of physiologists to the particular modifications that this property undergoes in the different parts. 33. Like the skin, the mucous membranes have their chorion: it is thick on the palate, gums, and pituitary membrane, delicate in the stomach and intestines, not very distinct in the bladder, gall bladder, and excretory ducts. It appears to be formed of condensed cellular strata, strongly united, as in the skin. Maceration develops this texture in a very sensible manner. There is nevertheless this difference, that in dropsy the cutaneous chorion rises and resolves itself into distinct cellules, that become filled with water, whilst no such change takes place in the mucous chorion under similar circumstances. Does this difference in the morbid state suppose a dissimilarity of structure? Certainly not; for the synovial membrane is evidently of the same nature as the serous membranes; and nevertheless it does not participate in the hydropic diathesis which often affects them universally. It would be curious to expose mucous membranes to the action of tan, to see if they would present the same phenomena as the skin. SECTION IV. OF THE GLANDS OF MUCOUS MEMBRANES.