52 ORGANS OF DIGESTION. 



yield very readily'to putrefaction, and are quickly reduced to a 

 pulpy state by the action of the mineral acids. Caustics of all 

 kinds act more promptly on them than on the skin, owing to the 

 protection of the latter by a dry epidermis ; Bichat states, that in 

 the practice of the Hotel Dieu, this effect is frequently exempli- 

 fied* by the administration of lunar caustic among the common 

 people for the purpose of poisoning. The nitric acid leaving the 

 silver, quickly applies itself to^the mucous membrane of the sto- 

 mach, and disorganizing it, forms a whitish eschar, which, if life 

 be preserved long enough, is finally detached in a membranous 

 form. 



One of the remarkable properties of the mucous surfaces of the 

 stomach and intestines is, that of coagulating milk. According 

 to the experiments of Spallanzani, the gastric juice, in the living 

 state, assists in this change ; but it is perfectly well known in do- 

 mestic affairs, that the dried stomach of a calf, where the juices 

 have been completely evaporated, is also productive of it. The 

 observations of the same author led him to conclude, that the 

 peritoneal and the muscular tunics of the stomach are insuffi- 

 cient to produce this effect. 



The internal surface of all the mucous membranes is furnished 

 with small projecting points or spiculas, called papillae or villi. 

 They are particularly conspicuous and numerous, as mentioned, 

 on the upper surface of the tongue and in the small intestine, 

 and bear an analogy of function and organization with the very 

 fine papilla? which are seen invariably on the surface of the 

 cutis vera. These papilla? are invariably furnished with ner- 

 vous filaments, giving them a high degree of sensibility ; and 

 with an abundance of blood vessels. The term papillas has been 

 more exclusively applied to the projections on the surface of the 

 tongue, from their greater size; they are there also more distinctly 

 covered with an epidermis, frequently called epithelium, or peri- 

 glottis. The villi, from their connexion with the process of di- 

 gestion, have been emphatically denominated the roots of ani- 

 mals. According to M. Beclard,* who has examined them upon 

 a plan of his own contrivance well suited to accurate microsco- 

 pic observations, .they are presented under a diversity of shapes. 

 Those of the pyloric half of the stomach, and of the duodenum 

 being broader than they are long, are composed of very small 



* Anat. Gen. p. 253. These notions are not, however, in unison with my own, 

 as just stated. SECT. III. 



