238 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



D. INTESTINAL DIGESTION. 



After the food has passed through the pyloric orifice of the stomach and has 

 entered the small intestine it undergoes its most profound digestive changes. 

 Intestinal digestion is carried out mainly while the food is passing through 

 the small intestine, although, as we shall see, the process is completed during 

 the slower passage through the large intestine. Intestinal digestion is effected 

 through the combined action of three secretions namely, the pancreatic juice, 

 the bile, and the intestinal juice. The three secretions act together upon the 

 food, but for the sake of clearness it is advisable to consider each one separately 

 as to its properties and its digestive action. 



Composition of Pancreatic Juice. Pancreatic juice is the secretion of 

 the pancreatic gland. In man the main duct of the gland opens into the 

 duodenum, in common with the bile-duct, about 8 to 10 cm. below the opening 

 of the pylorus. In some of the other mammals the arrangement is different : 

 in dogs, for example, there are two ducts, one opening into the duodenum, 

 together with the bile-duct, about 3 to 5 cm. below the opening of the 

 pylorus, and one some 3 to 5 cm. farther down. In rabbits the principal 

 duct opens separately into the duodenum about 35 cm. below the opening 

 of the bile-duct. For details as to the act of secretion, its time-relations to 

 the ingestion of food, its quantity, etc., the reader is referred to the section on 

 Secretion. Most of our exact knowledge of the properties of the pancreatic 

 secretion has been obtained either from experiments upon lower animals, 

 especially the dog and the rabbit, in which it is possible to establish a pan- 

 creatic fistula and to collect the normal juice, or from experiments with arti- 

 ficial pancreatic juice prepared from extracts of the gland. Various methods 

 have been used in making pancreatic fistulae : usually the main duct of the 

 gland, which in the two animals named is separate from the bile-duct, is 

 exposed and a canula is inserted. A better method, devised by Heidenhain, 

 consists in cutting out the piece of duodenum into which the main duct opens 

 and sewing this isolated piece to the abdominal wall so as to make a permanent 

 fistula, the continuity of the intestinal tract in this case being re-established, 

 of course, by sutures. A simple method of obtaining normal pancreatic juice 

 from the rabbit is described by Ratchford. 1 In his method the portion of 

 the duodenum into which the main duct opens is resected and cut open along 

 the border opposite to the mesenteric attachment. The mouth of the duct is 

 seen as a small papilla projecting from the surface of the mucous membrane. 

 Through the papilla a small glass canula may be passed into the duct, and the 

 secretion, which flows slowly, may be collected for several hours. The total 

 quantity obtainable by this means from a rabbit is small about 1 c.c. but it 

 is sufficient for the demonstration of some of the important properties of pan- 

 creatic juice, especially its action upon fats. As obtained by these methods, 

 the secretion is found to be a clear, colorless, alkaline liquid. The secretion 

 obtained from dogs is thick and glairy, and forms a coagulum upon standing, 

 1 Journal of Physiology, vol. xii., 1891, p. 72. 



