9 8 



HUMAN PHYSIOLOGY. 



intestine the mucous membrane contains an enormous number of tubular 

 glands (Lieberkiihn's), formed by an inversion of the basement membrane 

 and lined by epithelial cells. The common secretion of these intestinal 

 glands forms the intestinal juice. This is a thin, opalescent, slightly yellow- 

 ish fluid, alkaline in reaction, and contains water, salts and proteid matter. 



The function of the intestinal juice is but incompletely known. It appears 

 to have the power of converting starch into dextrose. It is doubtful whether 

 it is capable of digesting either proteins or fats. Its most distinctive action is 

 the inversion of saccharose into dextrose and levulose, maltose into dextrose, 

 and lactose into dextrose and galactose, thus preparing them for absorption. 

 This change is dependent on the presence of three ferment bodies known 

 as saccharase, maltase and lactose. 



By reason of the presence of the enzyme erepsin, the peptones, the final 

 products of the digestion of proteins by the gastric and pancreatic juices, 

 are still further reduced to the condition of ammo acids. 



The pancreatic juice is secreted by the pancreas, a flattened gland, about 

 six inches long, running transversely across the posterior wall of the abdomen 

 behind the stomach; its duct opens into the duodenum. 



FIG. 14. ONE SACCULE OP THE PANCREAS OP THE RABBIT IN DIFFERENT STATES OF 



ACTIVITY. (After Kiihne and Lea.) 



A. After a period of rest, in which case the outlines of the cells are indistinct and 

 the inner zone i.e., the part of the cells (a) next the lumen (c) is broad and filled 

 with fine granules. B. After the gland has poured out its secretion, when the cell 

 outlined (d) are clearer, the granular zone (a) is smaller, and the clear outer zone is 

 wider. 



The pancreas is similar in structure to the salivary glands, and consists 

 of the system of ducts terminating in acini. The acini are tubular or flask- 

 shaped, and consist of a basement membrane lined by a layer of cylindric, 

 conic cells, which encroach upon the lumen of the acini. The cells exhibit 

 a difference in their structure (Fig. 14), and may be said to consist of two 



