DIGESTION. 243 DIGESTION. giderable portion of tlic albuminates ontors tlip duodenum in an undissolved stale, and wliieh will be explained when we consider the innt Fig. 4. The mn: . ,,f the stomach and liver, wliirli are raised tn sho« the iliHuli'iiniii nml imnrron.'s. St. stomach; p. its |i.vlori<- end: ;, liver; /.: i:iM-haMer ; d, duodenum. extendiuK from the jiyloric end "( the stom- ach to the front, where the superior mesenteric nrt<"r.v (sni) crosses the intestines; pa, pancreas: sp, spleen: a, abdo- minal aorta. which the intestinal juiec — the tluid seerctcd by the various elands lying in the mucous membrane of the small intestine — takes in the digestive process. On comparing the experiments made on dogs with those made on Catharine Kiitt, it ap- pears that in the human subject the gastric di- gestion of the albuminates is much more imper- fect than even in the dog. The process of gastric digestion is slow. -Ac- cording to Beatmiont's researches on Alexis Saint Martin, the mean time required for the digestion of ordinary animal food, such as butcher's meat, fowl, and "game, was from two hours and three- quarters to four hours. Frerichs and Bon- ders maintain that the absorption of the pep- tones commences in the stomach ; but the view generally adopted is, that the albuminates, etc., which are con- verted into peptones, I, are for the most part taken up by the lac- teals. The rapidity with which aqueous e sidutions of iodide of potassiimi, the alka- d line carbonates, lac- tates, citrates, etc., pass into the blood, and thence into the urine, saliva, etc., Fig 5. Vertical and loneitudi- j,,j^^^.g ^]^^^^ ^,,p .,^. nal section of thesinallniti'stme . t ii ■ i .„t InthelowerportoftUeHunum, sorption of Ihuds must BhoKinit the general arrange- take place verv short- ment of its coats. Iv after they are swal- a. villi: /), intestinal tubes or '. i ii • follicles of I^ieherkuhn: c. sub- lowed, and there is mncous nrefjlar tissue; <f,clrcu- little doubt that the lar n.u.scular Hhres: e. longltu- (.joodvessels (capilla- dlnal muscular fibres. . , , ~ ' , ries) of the stomach constitute the principal channel through which they pass out of the intestinal tract into the blood. As the veins of the stomach, which are formed by the union of these capillaries, con- tribute to form the portal vein (see C'lRrri.A- TION ) . the absorbed matters pass directly to the liver, anil probably stimulate it to increased se- cretion (Fig. 4). M>, ^ ((i) Wo must now follow the progress of the semi-fluid mass, known as the c/i,i/mc, from the stomach into the small intestine, and notice the changes which arc collectively impressed upon it, and are known as chjilif'icalion or intestinal di- gestion. lUit before we can satisfactorily do this, we must say a few words re- garding the intestinal mucous membrane, with its variims glands, etc., and on the changes which take place in it during digestion. The mucous membrane of the small inlestinc resembles that of the stomach in so far as it is of considerable thick- ness, and consists in a great measure of laterally grouped tubes. The reader is referred to Fig. 5. which exhibits a section of the mucous mem- brane of the small intestine in the dog. The tubes, which form the great mass of the middle portion of the section marked b. are commonly called the follicles of Liehcrhuhn, although they were first de- scribed by Bninner. They are p,o g Two villi, straight, nearlv uniform in denuded of epitheli- diameter throughout their en- ""'• ^i*!' *'!•■ lacteal ,. , ., '^i ,, , vessels in their inte- tire length, and are parallel rjor. to one another, and perpen- a. limitary mem- dicular to the inner surface brnne of the villus; . ,, ,,.... 1.1 ^, basis of the same; of the small intestine on which f. dilated blind ex- they open. Nothing is known tremity of the lac- of the exact nature of their teaU^rf, trunk of the •secretion ; but in association with the secretions of other glands, they com- bine to yield the intestinal juice whose charac- ters and uses will shortly come under our notice. The projecting bodies marked a in the figure are termed the villi : they are minute processes of the mucous membrane of the small intestine, and obviously serve to increase to a great extent the amount of absorbing mucous membrane. They first appear in the duodenum, where they seem to develop themselves as elongations of the partitions between the cells or pits into which the tubes open. Comparatively scanty in num- ber at first, they become very numerous (cover- ing the whole surface) in the further jiart of the duodenum and the rest of the small intestines, giving to the mucous membrane a velvet-like or pilous appearance; they finally cease at the ileocecal valve, which forms the boundary be- tween the small and large intestine. In man, they are conical in sha])e. and measure from one-forty-fifth to one-sixtieth of an inch in length. They vary much in .shape and size in the lower mammals and in birds. ( In carnivorous animals, as the dog, they are longer and more filiform than in man.) The structure of a villus (Fig. 6) is somewhat complicated, but we must endeavor to explain it, because, without tolerably accurate knowledge on this point, no one can understand how most of the essential elements of food (the albumi- nates and fatty matters) make their way from the intestine to the blood. Each villus is pro- vided with an abundant set of capillaries, which doubtless absorb fluid matters, which thus find their way directly from the bowels into the blood
