DIGESTION. 291 



The thin pultaceous chyme, therefore, which, during the whole period 

 of gastric digestion, is being constantly squeezed or strained through 

 the pyloric orifice into the duodenum, consists of albuminous matter, 

 broken down, dissolving and half dissolved; fatty matter broken down 

 and melted, but not dissolved at all; starch very slowly in process of 

 conversion into sugar, and as it becomes sugar, also dissolving in the 

 fluids with which it is mixed; while, with these are mingled gastric fluid, 

 and fluid that has been swallowed, together with such portions of the 

 food as are not digestible, and will be finally expelled as part of the 

 faBces. 



On the entrance of the chyme into the duodenum, it is subjected 

 to the influence of the bile and pancreatic juice, which are then poured 

 out, and also to that of the succus entericus. All these secretions have 

 a more or less alkaline reaction, and by their admixture with the gastric 

 chyme, its acidity become less and less until at length, at about the 

 middle of the small intestine, the reaction becomes alkaline and con- 

 tinues so as far as the ileo-caecal valve. 



The special digestive functions of the small intestine may be taken in 

 the following order: 



(1.) One important duty of the small intestine is the alteration of 

 the fat in such a manner as to make it fit for absorption; and there is no 

 doubt that this change is chiefly effected in the upper part of the small 

 intestine. What is the exact share of the process, however, allotted re- 

 spectively to the bile, to the pancreatic secretion, and to the intestinal 

 juice, is still uncertain. The fat is changed in two ways, (a.) To a 

 slight extent it is chemically decomposed by the alkaline secretions with 

 which it is mingled, and a soap is the result, (b.) It is emulsionized, 

 i. e., its particles are minutely subdivided and diffused, so that the mix- 

 ture assumes the condition of a milky fluid or emulsion. As will be seen 

 in the next Chapter, most of the fat is absorbed by the lacteals of the 

 intestine, but a small part, which is saponified, is also absorbed by the 

 blood-vessels. 



(2.) The albuminous substances which have been partly dissolved in 

 the stomach, and have not been absorbed, are subjected to the action of 

 the pancreatic and intestinal secretions. The pepsin is rendered inert 

 by being precipitated together with the gastric peptones and parapep- 

 tones, as soon as the chyme meets with bile. By these means the pan- 

 creatic ferment trypsin is enabled to proceed with the further conversion 

 of the parapeptones into peptones, and of part of the peptones (hemipep- 

 tone, Kiihne) intoleucin and tyrosin. Albuminous substances, which are 

 chemically altered in the process of digestion (peptones) and gelatinous 

 matters similarly changed, are absorbed by the blood-vessels and lym- 

 phatics of the intestinal mucous membrane. Albuminous matters, in 

 state of solution, which have not undergone the peptonic change, are 



