DIGESTION. 183 



uniting with the splenic and gastric veins, forms the portal vein. The nerves 

 are derived from the lower part of the semi- lunar ganglia. The branches 

 follow the blood-vessels and become associated with two plexuses, one 

 (Auerbach's) lying between the muscle coats, the other (Meissner's) lying 

 in the submucous coat. To this nerve net, composed of nerve cells and 

 nerve processes, found in connection with the muscle coats of the stomach, 

 of the small and of the large intestine as well, the term myenteric plexus 

 has been given. The lymphatics, which originate in the mucous and muscle 

 coats, are very abundant. They unite to form those vessels seen in the 

 mesentery and empty into the thoracic duct. 



Intestinal Glands. The gland apparatus of the intestine by which 

 the intestinal juice is secreted consists of the duodenal (Brunner's) and the 

 intestinal (Lieberkiihn's) glands. 



The duodenal glands are situated beneath the mucous membrane and 

 open by a short wide duct on its free surface. They are racemose glands 

 lined by nucleated epithelium. The secretion of these glands is clear, 

 slightly viscid, and alkaline. Its chemic composition and functions are 

 unknown. 



The intestinal glands or follicles are distributed throughout the entire 

 mucous membrane in enormous numbers. They are formed mainly by 

 an inversion of the mucous membrane and hence open on its free surface. 

 Each tubule consists of a thin basement membrane lined by a layer of spheric 

 epithelial cells, some of which undergo distention by mucin and become 

 converted into mucous or goblet cells. The epithelial secreting cells consist 

 of granular protoplasm containing a well-defined nucleus. The intestinal 

 follicles constitute the apparatus which secretes the chief portion of the in- 

 testinal juice. 



Intestinal Juice. Owing to its admixture with other secretions and 

 to the profound disturbance of the digestive function caused by the establish- 

 ment of intestinal fistulae, this fluid has rarely been obtained in a state of 

 purity or in quantities sufficient for accurate analyses or for experimental 

 purposes. Its physiologic properties and functions are therefore imperfectly 

 known. Various attempts have been made by physiologists, by the employ- 

 ment of different methods, to obtain this secretion. The method usually 

 employed is that of Thiry and Vella. This consists in dividing the intestine 

 at two places, about eight or ten inches apart, restoring the continuity of the 

 intestine, and then uniting the two ends of the resected portion to the edges of 

 two openings in the abdominal walls. The resected portion, being supplied 

 with blood-vessels and nerves, maintains its nutrition and secretes a more or 

 less normal juice. 



When obtained from a dog under these circumstances the intestinal 

 juice is watery in consistence, slightly opalescent, light yellow in color, 

 alkaline in reaction, with a specific gravity of i.oio. Chemic analysis 

 reveals the presence of proteins, mucin, and sodium carbonate. 



The intestinal juice obtained by Tubbey and Manning from a small 

 portion of the human intestine (ileum) was opalescent, occasionally brownish 

 in color, alkaline, and had a specific gravity of 1.006. On the addition of 

 hydrochloric acid, carbonic acid was given off, showing the presence of 

 carbonates. It contained proteins and mucins. 



