The mucous corion is very various as to thickness; it differs in this respect in each organ. That of the gums and the palate is the thickest of all. Then come those of the nasal fossæ and the stomach, then those of the small intestines and the gall-bladder, then those of the large intestines, of the urinary bladder, the urethra and the other excretories, until it begins at length to become so fine as to appear transparent like a serous surface when it is removed with care. Finally, the finest and most delicate is that of the sinuses of the face and the interior of the ear; the arachnoides is often coarser. I have called the texture within the ear mucous, though all anatomists call the membrane of the cavities of this organ periosteum. In fact, 1st, we see it evidently continued with the pituitary membrane, by means of the elongation of the Eustachian tube. 2d. We find it constantly moistened by a mucous fluid which this canal serves to convey out, a character foreign to the periosteum, which, like the fibrous membranes, always adheres by both its surfaces. 3d. No fibre can be distinguished in it. 4th. Its fungous appearance, though white and soft, and the ease with which it is torn, are evident attributes of the mucous membranes. Every thing proves that the membrane of the tympanum, that of the meatus, &c. belong to the system of which we are treating. Thus in catarrhs of the pituitary membrane, and of that of the fauces, we most often find that the ear is affected; thus the ear is, like the mucous surfaces, the seat of hemorrhage, thus polypi arise in it, as in the nose and on the surface of the womb. We consider as a sign of deposition of pus in the ear, every purulent discharge coming from that cavity. But how can we conceive of a purulent collection in a part in which there is hardly any cellular texture, in a part wholly osseous? Besides the fibrous system, to which the periosteum of the tympanum belongs, hardly ever suppurates, as we know. Every thing then induces us to believe that these discharges are only the effect of a catarrh of the ear, a catarrh which is sometimes acute and sometimes chronic. I have moreover a recent and decisive fact upon this point; the body of a man subject to these discharges during life exhibited a remarkable thickness and redness of the membrane of the tympanum, but without the least trace of erosion. The ear suppurates like the urethra, the vagina, &c. it is not a new fluid which is formed by suppuration; it is that which naturally comes from the meatus which increases in quantity and comes through a preternatural opening of the membrane of the tympanum.