70. I have already examined many of the functions of mucous membranes. I have considered them (1) As one of the grand emunctories of the animal economy. (2) As performing the same functions with respect to heterogeneous bodies, which may be within our organs, as the skin does with regard to the bodies with which it may be in contact. (3) As facilitating the passage of foreign bodies by means of the mucous fluid by which they are lubricated. It remains for me to examine three questions much agitated at this time. (1) If the mucous membranes have any influence over the redness of the blood. (2) If they exhale. (3) If the absorbents arise from them; and if absorption consequently takes place there. 71. The remarkable redness of these membranes, the analogy of respiration, during which the blood becomes changed in colour through the mucous surface of the bronchi, the well-known experiment of a bladder filled with blood and placed in oxygen gas, by which this fluid becomes also changed in colour,--have led to the belief, that the blood, being separated from the atmospheric air merely by a very fine pellicle on certain mucous surfaces, as the pituitary membrane, the palatine, the glans, &c., would there also take a brighter red colour, either by parting with a portion of carbonic acid gas, or by combining with the oxygen of the atmosphere, and that these membranes thus fulfilled functions accessory to those of the lungs. The experiments of Jurine upon the cutaneous organ, experiments adopted by many celebrated physicians, appear also to favour the reality of that conjecture.