83. Why do polypi, a kind of affection peculiar to mucous membranes, seldom arise but at the origins of these membranes in the vicinity of the skin, as in the nose, pharynx, vagina, &c., and not in their more internal portions, as in the stomach, intestines, &c.? Does this arise from the peculiarity of the texture that I have shown mucous membranes to have in the vicinity of those places where they arise from the skin, or must we attribute this fact to the more numerous causes of irritation which act upon the origins of these cavities? 84. Are not aphthæ an isolated inflammatory affection of the glands of the mucous membranes, whilst catarrhs are characterized by a general inflammation of all the parts of these membranes? THE END. CHARLES WOOD, Printer, Poppin's Court, Fleet Street, London. FOOTNOTES: [A] The following questions have been much disputed: Is there a cystic and an hepatic bile? Is the one of a different nature from the other? Does their quantity increase or vary? &c. Contrary, and even opposite, opinions have been supported by numerous experiments made upon living animals, as Haller as well observed. These experiments, though at first sight contradictory, in reality are not so, as I have had the opportunity of convincing myself, by repeating them in the different stages of digestion, and during the abstinence of the animal, which previously had never been done with precision. The following are what I have observed in dogs that I have used in my experiments. (1) During abstinence, the stomach and the small intestines being empty, yellowish clear bile was found in the hepatic duct and ductus communis choledochus; the surface of the duodenum and jejunum were stained by a bile which had the same appearance; the gall bladder was very much distended by a greenish bitter bile, which was deeper in colour and more in quantity, according to the length of the abstinence. (2) During the gastric digestion, which may be prolonged for a sufficient length of time by giving the dog large pieces of meat, which he swallows without chewing, appearances were similar. (3) At the commencement of intestinal digestion, the bile in the hepatic duct was always found yellowish; that of the ductus communis choledochus deeper in colour; the gall bladder not so full, and its bile becoming already more clear. (4) Towards the end of digestion, and immediately after it, the bile of the hepatic duct, of the ductus communis choledochus, that contained in the gall bladder, and that which was spread over the duodenum, were exactly of the same colour as the common hepatic bile, a clear yellow, having but little bitterness. The gall bladder was but half full; it was not contracted, but flaccid.