INTESTINAL DIGESTION. 357 



CHAPTER IX. 



INTESTINAL DIGESTION. DEF^HC A TION. 



Physiological anatomy of the small intestine Glands of Brunner Intestinal tubules, or follicles ot Lieberkuhn 

 Solitary glands, or follicles, and the patches of Peyer Intestinal juice General properties of the intestinal 

 juiee Action of the intestinal juice in digestion Pancreatic juice Action of the pancreatic juice in digestion 

 Destruction of the pancreas Cases of fatty diarrhoea Action of the pancreatic juice upon starchy, saccharine, 

 and nitrogenized principles Action of the bile in digestion Biliary fistula General constitution of the bile 

 Variations in the flow of bile Movements of the small intestine Peristaltic and antiperistaltic movements 

 Function of the gases in the small intestine Influence of the nervous system upon the peristaltic movements 

 Physiological anatomy of the large intestine Digestion in the large intestine Contents of the large intestine- 

 Composition of the faeces Excretine and excretoleic acid Stercorine Movements of the large intestine Defse- 

 cation Gases found in the alimentary canal. 



Physiological Anatomy of the Small Intestine. 



THE small intestine, so called on account of its small size as compared with the rest 

 of the intestinal tract, is the long, cylindrical tuhe which occupies the greatest part of 

 the abdominal cavity. This must now be regarded as the most important division of the 

 digestive system ; and its physiological anatomy, together with that of the great glands 

 which discharge their secretions into its cavity, is indispensable as an introduction to 

 the study of intestinal digestion. As it is in the small intestine that the final elaboration 

 of most of the alimentary principles takes place, and here, also, that these principles are 

 taken into the circulating fluid, we shall find, in our study of its anatomy, certain parts 

 which are concerned in digestion, and others which, as far as we know, are connected 

 only with the function of absorption. It will be most convenient, however, to consider, 

 in this connection, all the structures found in the small intestine which possess physio- 

 logical interest. 



The small intestine, extending from the pyloric extremity of the stomach to the ileo- 

 cccal valve, is held to the spinal column by a double fold of serous membrane, called the 

 mesentery. As the peritoneum which lines the cavity of the abdomen passes from 

 either side to the spinal column it comes together in a double fold just in front of the 

 great vessels along the spine, and, passing forward, splits again into two layers, which 

 become continuous with each other and enclose the intestine, forming its external coat. 

 The width of the mesentery is usually from three to four inches; but, at the commence- 

 ment and the termination of the small intestine, it suddenly becomes shorter, binding the 

 duodenum and that portion of the intestine which opens into the caput coli closely to the 

 subjacent parts. The mesentery thus keeps the intestine in place but allows of a certain 

 amount of motion, so that the tube may become convoluted, accommodating itself to the 

 size and form of the abdominal cavity. The form of these convolutions is irregular and 

 is continually changing. * 



The length of the small intestine, in situ, is probably from fifteen to eighteen feet 

 (Sappey) ; but the canal is very distensible, and its dimensions are subject to constant 

 variations. When separated from the mesentery and measured without stretching, its 

 length has been found to be, on an average, about twenty feet. Its diameter is about 

 one and a quarter inch. 



The small intestine has been divided into three portions, which present anatomical 

 : and physiological peculiarities, more or less marked. These are the duodenum, the jeju- 

 num, and the ileum. 



The duodenum has received its name from the fact that it is about the length of the 

 breadth of twelve fingers, or from eight to ten inches. This portion of the intestine is 

 considerably wider than the constricted, pyloric end of the stomach, with which it is con- 

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