27. We distinguish only a kind of gelatinous juice intermediate to the corps papillaire and epidermis, and most commonly it is not even apparent; I have never been able to observe more with certainty. In examining the skin of a Negro with attention, the epidermis being detached, I have seen the external surface of the chorion tinged with black, and that was all. Further, whatever this corpus mucosum may be, it certainly does not exist in mucous membranes, since they do not participate in the colour of the integuments. The heat of the sun, which darkens these in white people, does not appear to act upon the commencement of these membranes, which are equally exposed with them to its influence, as is seen in the red borders of the lips, &c. Nevertheless, I have many times remarked on the palates of dogs, which have been the subjects of my experiments, similar spots to those which have marked their skin. 28. The sensibility of the skin is principally owing to the corps papillaire; that of the mucous membranes, exactly analogous to that of the skin, appears to me to arise from the same cause. The nervous papillæ of these membranes cannot be questioned: at their origin, where they dip into the cavities, even in the commencement of these cavities, as on the tongue, the palate, the internal surface of the alæ nasi, on the glans, in the fossa naviculare, on the inside of the lips, &c., inspection is sufficient to demonstrate them. But, we ask, do these papillæ exist also in those parts of mucous membranes which are more remote from the surface of the body? Analogy answers in the affirmative, since sensibility is the same there as at their origin; but inspection proves it in a no less certain manner. I believe, that the villosities with which we see them everywhere thickly furnished are nothing else than these papillæ.