DIGESTION. 242 DIGESTION. disproved the favorite tlieoiy of that period, which ascribed all the chan<;es which the food underwent in the stomach to a species of tritura- tion. The subject of artificial digcslioii, or di- gestion out of the body. has. sini.-e that period, iK'cn carefully investifiatcd hy many observers, and there is now no doubt that the changes which the food undcrjrocs in the stomach are essentially chemical, and not mechanical. Two years before Beaumont's experiments. Dr. Prout had ascertained not only that an acid fluid is secreted by the gastric mucous membrane of rabbits, hares, horses, dogs, etc., during diges- tion, but that the acid is the muriatic or hydro- chloric acid, and it was supposed that the .sol- vent action of tlie gastric juice was due to this source. But exi)eriments showed that the solvent action is not due simply to the acid of the gastric juice, and that the latter must contain some other ingredients which, either alone or in combination with the acid, can exercise this power. It was then discovered that the addition of a portion of the gastric mucous membrane to water acidified with hydrochloric acid produced a perfect digestive fluid, due attention licing paid to the temperature, which should be kept at about 100° F.. or about the normal tcmi)erature of the interior of the nnimnl body. Later observa- tions showed that we can obtain from the gastric mucous membrane the special organic matter on which its digestive power depends, and to this svibstance the name of pcpxin has been given. The two essential elements of the gastric juice are, then: (1) a free acid, which in some cases seems to he hydrochloric alnne. and in others a mixture of hydrochloric and lactic acids: and (2) an organic matter, which is found on analysis to be highly nitrogenous, and to he allied to the albiuninates, and which we term pepsin. The best analysis of human gastric juice is that made by Schmidt of Dorpat. who, in 18.i3, had an excel- lent and rare opportunity of examining it in the case of an Esthoninn peasant, Catharine Kiltt. aged thirty-five years, and weighing abmit ll.S pounds, in whom there had existed for three years a gastric fistula or opening, three or four lines in diameter, under the left breast, t)etween the cartilages oiF the ninth and tenth ribs. The in- troduction of drv peas and a little water into the stomach through the opening (even in the morning, on an emptv stomach) occasioned the secretion of from five to seven ounces of a dear limpid fluid with an acid reaction, which, however, was much less strong than Schmidt had observed in previous experiments on the gas- tric juice of dogs and sheep, in which he had artificiall.v established similar fistulous openings. The following table gives the mean of two anal- vses nf the gastric juice of Catharine Kiltt. with corresponding mean results of the same fluid in the sheep, a purely herbivorous animal, and in the dog, a purely carnivorous animal: Humnn KOstrlc Juice WBt»r Solid con«tltnent« FepHJn H,Tdrochlorlr nrM ' Chlorldwt of Rodlum, ft*-, i Pboephati^ ! 994.40 s.oo 320 11.20 'illK 0.12 Sheep's Kastrlc Jnlce see. IS 13.8S 4.20 i.se «.oo 3.09 Dok'b Biwtrlc Juico 971.17 28.83 17.61 2.70 B.S8 2.74 The only impurity that could affect these anal- yses is the saliva that possibly might have been swallowed. nie quantity of the gastric juice secreted in twenty- four hours was determined by Bidder and Schmidi (Die V' ;(/iji(i/Hi;.s'.v(i/'/r, etc. I in the sheep to be one-eighth, and in the dog one-tenth of the weight of the bod.v. If the latter ratio were true for men, a man nf 140 pounds' weight would secrete about H pounds of this iluid daily. In the case of Catharine Kiitt, the mean daily quantity amounted to no less tlian 31 pounds, or (o more than a fourth part of the weight of her bodv. On this calculation, a man of 140 pounds weight would daily secrete 37 pound.s of gastric juice. The u.ses of this fluid in reference to digestion are clear. It serves not onl.v to dissolve, but also to modify the nitrogenous elements of the food (such as albumen, fibrin, casein, and, in short, all animal food except fat, and the blood-forming portion of vegetable food), converting tliem into new substances, tenncd prploitr/i, which, al- though the.v coincide in their chemical composi- tion, and in many of their physical properties, with the subst;inccs from which they are derived, diflcr essentially from them in their more ready solubility in water, and in various chemical rela- tions. Thus, albumen is converted by the gastric juice into albumen-peptone, fibrin into fibrin- peptone, etc. According to the investigations of Meissner, the albuminates are simultaneously de- composed or broken up into peptones and sub- stances which he terms ptirapiptoiirs. which lat- ter are not further changed by the action of the gastric juice, but are converted into peptones by the actiim of the pancreatic juice, with which they come in contact in the duodenum. All the best observers agree that the ga.stric juice exerts no apparent action on the non-nitrog- enous articles of food — namely, the fats and the carbohydrates (sugar, starch, etc, I : as, how- ever, the fats exert a favorable infiuencc on the digestion of nitrogenous matters, it is probable that they undergo some slight, although not ap- preciable, modification. (Gelatin and the gelat- inous tissues arc as far as is known, the only nitrogenous articles of food which are not con- verted into peptones and parapeptones by the action of the gastric juice, .lthough the main object of the gastric juice is to dissolve the albuminates, etc. (e.g. the con- tents of the egg, fiesh. cheese, etc.), it appears from the exiieriments of I.ehmann, Sclmiidt, and others, that it cannot dissolve the (iiianlitv ne<'es- sarv for the due nutrition of the organism. .c- cording to I.ehmann, gastric juice can only dis- solve one-twentieth of its weight of coagulated albumen, whilf Schmidt makes the quantity as low as one-fort.v-fifth. Xow, since a dog secretes about one-tenth of its weight of gastric juice daily, it would onl.v be able — even taking Leh- mann's estimate, which is more than twice aa high as Schmidt's — to digest five i)arts of dry or coagulateil albumen for every 1000 parts of it.s weight; but a dog, in order to keep in condition on an exclusive flesh diet — and this is its natural food — should take M parts of flesh, containing 10 parts of dry albuminates, for every lOOn parts of its weight. Hence its gastric juice only suf- fices for the digestion of half (he albuminates necessary for nutrition — a result which is in accordance with the observed fact that a eon-
