51. As respects the other hollow organs, it is difficult to examine the circulation of their adjacent viscera during their plenitude or vacuity; for their vessels are not superficial, as in the omentum, or insulated, as in the spleen; therefore, to decide this question concerning them, we can only observe the state of the mucous membranes upon their internal surface. Now they have always appeared to me as red during the contraction as during the dilatation of the organs. Finally, I give this only as a fact, without pretending to draw any inference from it opposed to the common opinion. It is, in fact, possible, that though the quantity of blood be always nearly the same, the rapidity of the circulation may increase; and consequently, in a given time, more of this fluid will be sent there during the plenitude of the viscera. This appears to be necessary for the secretion of the mucous fluids, which are then more abundant.
OF THE VARIATIONS IN THE ORGANIZATION OF MUCOUS MEMBRANES IN DIFFERENT REGIONS.
52. The assemblage of the epidermis, corps papillaire, chorion, glands, and vessels, constitutes in the mucous membranes their intimate organization, which presents very considerable variations in the different regions in which they are examined. I shall point out only the principal of them; for in no different parts do these membranes present the same appearance, and in order to describe all their differences they should all be examined.
53. One of these variations is that which the aspect of mucous membranes presents at their origin, when compared with their appearance in the more remote parts of the organs. Compare, for instance, the surface of the glans, the inner surface of the lips, the orifice of the urethra, &c., with any portion of the inner surfaces of the stomach, intestines, &c. In the first the corps papillaire will be seen slightly marked, and offering no villous character, the epidermis thick, very distinct, and easily separated, the chorion very evident, the vessels rather less superficial, the mucous glands numerous and very large, more especially in the mouth; in the other characters almost opposite will be observed; we should say, that the mucous membranes have at their origin a structure of a middle kind between the skin and their deeper portions.