398 



STOMACH AND INTESTINE. 



and instantaneous character of this change, 

 which is only paralleled by the similar efficacy of 

 the pancreatic juice, quite distinguishes it from 

 that slower and less perfect metamorphosis 

 which other animal secretions and substances 

 are able to produce. The absence of the high 

 temperature, and the evident putrefaction, 

 which are generally associated with the action 

 of these latter, still further distinguish the 

 specific metamorphosis due to these secretions. 

 But the substance and secretion of any one 

 of the salivary structures, seems insufficient 

 for the production of this agent. The sub- 

 maxillary glands, and the mucous membrane 

 of the mouth can, however, together furnish it 

 without any aid from the parotid.* 



The mastication and insalivation of the 

 food is immediately followed by its deglutition, 

 which propels the pulpy or semifluid mass it 

 now forms into the stomach. 



On entering this organ, it is subjected to a 

 special act of gastric digestion. 



The energetic action of the mixed saliva 

 is not affected by the gastric juice secreted by 

 the stomach. Much of the starch of the food 

 is probably converted into sugar during the 

 short sojourn of the aliment in this cavity. 

 The sugar thus produced would seem to be 

 absorbed by the vessels of the gastric mucous 

 membrane with extraordinary rapidity. The 

 water, salts, and soluble organic compounds 

 of the food are similarly taken up. And the 

 gastric juice attacks and dissolves the pro- 

 tinous element of the food. The perfect- 

 ness of this process of solution depends on 

 the mechanical state of the substances con- 

 cerned, and the quantity and efficiency of the 

 active liquid. Of the resulting solution or 

 peptone, part is immediately absorbed by the 

 gastric vessels, while part passes on into the 

 duodenum, in company with portions of pro- 

 tein, which have not yet yielded to the solvent 

 process. Many of these portions ultimately 

 become dissolved, and with the peptone that 

 accompanies them, are taken up by the veins 

 of the intestine. 



The intestinal digestion of the food is a still 

 more complex act. The chyme that enters 

 the duodenum probably contains all the 

 alimentary principles originally present in the 

 food. But it includes them in very different 

 proportions compared with their original 

 quantities. And these proportions have very 

 diverse destinies in connection with the di- 

 gestive process. 



The watery ingredient of the food, and the 

 salts it introduces, probably have but to 

 complete their absorption. The soluble cal- 

 careous compounds appear, however, to de- 

 compose the bile ; and to combine with and 

 precipitate some of its acids in the shape of 

 insoluble salts of lime. 



* The experiment on which Bidder and Schmidt 

 (0/J. cit. p. 281) claim a similar efficacy for that of 

 the mucous membrane of the small intestine, appears 

 scarcely to warrant such a conclusion. Should its 

 accuracy be hereafter established, it would be inte- 

 resting to determine how far the glands of Brunn 

 were concerned in the process. 



The protein-compounds probably continue 

 their course through the intestine, still un- 

 dergoing (or rather completing) a gradual 

 process of solution under the action of the 

 gastric juice which accompanies them. 

 Whether any special intestinal juice* aids 

 this process, may at present be looked on as 

 doubtful. And whether the quantity of bile 

 usually added in the duodenum can really 

 hinder it, in the way in which Bidder and 

 Schmidt f have found that it suspends the 

 power of the gastric juice out of the body, 

 remains equally uncertain. 



The starch of the chyme would seem to 

 be converted into sugar, by the addition of a 

 further quantity of an agent, similar to that 

 which is furnished by the mixed secretions of 

 the salivary glands and mouth. At any rate, the 

 secretion of the pancreas, which is poured 

 out into the duodenum with the bile, is gifted 

 with the capacity of inducing this change just 

 as rapidly as the mixed saliva itself. 



The fatty constituents of the food are 

 probably absorbed by two channels, if not by 

 two processes. But the quantitative share 

 taken by each of these, remains at present 

 unknown. That a certain portion of the fat 

 contained in the food is taken up by the 

 vessels of the alimentary canal, seems evident 

 from the remarkable difference in the amount 

 of this substance, which is found in the organic 

 residuum of the portal blood, and that of the 

 ordinary systemic veins. | But the quantity 

 thus absorbed can scarcely be large. It ap- 

 pears to consist chiefly of the more fluid 

 elain. And hence there seem no valid grounds 

 for the supposition of much assistance being 

 given to its transudation from the digestive 

 canal into the veins, by means of a saponi- 

 fication with their alkaline blood. A much 

 greater quantity of the fatty matter of the 

 food is taken up by the lacteals of the villi, 

 and is conveyed from these vessels into the 

 thoracic duct. The microscopic details of 

 this process have already been mentioned. 

 Hence, it only remains for us to notice its 

 chemical relations to the various secretions 

 poured into the small intestine, in the lacteals 

 of which segment of the canal the white or 

 fatty chyle is chiefly found. 



The experiments and observations of 

 Claude Bernard would ascribe the formation 

 of chyle chiefly to the pancreatic juice. This 

 secretion appears to have the power of se- 

 parating fats into their acid and base. But 

 the fact, that such a saponification is pre- 

 vented by an admixture of gastric juice, or 

 any other acid, would justify us in doubting 

 whether the change really occurs in the 

 acid chyme of the living body. And all the 

 appearances of the chyle in the lacteals of the 

 villi concur in representing their fatty contents 

 as being not saponified, but merely in a state of 

 minute division. The production of this con- 

 dition, which closely corresponds to that of 



* Compare p. 349. 

 t Loc.cit. 



j See Heller's Archiv. vol. iii. p. 487. ; vol. iv. 

 pp. 1537. 97132. 



