DIGESTION. 



185 



tral and peripheral ends (Fig. 80). The central end, that bordering the 

 lumen of the acinus, is dark in appearance and filled with dark granules, 

 while the peripheral end is clear and homogeneous. The relative depth of 

 these two zones varies according to the functional activity of the gland. 

 During the intervals of digestion the granular layer is very deep and oc- 

 cupies almost the entire cell; after active digestion the granular layer is 

 very narrow, while the clear zone is largely increased in depth (Fig. 81.) 

 The blood-vessels of the pancreas are arranged around the acini in a 

 manner similar to that observed in the salivary glands. The ultimate ter- 

 minations of the nerves in the epithelium are probably by means of the 

 usual end-tufts. 



The Islands of Langerhans. Throughout the body of the pancreas and 

 especially in the outer extremity there are found between and among the 

 acini collections of globular cells arranged in the form or rods or columns, 

 separated from the acini and from one another by layers of connective 



FIG. 82. SECTION OF HUMAN 

 PANCREAS, INCLUDING SEVERAL ACINI 

 AND Two DUCTS. THE CELLS PRE- 

 SENT A CENTRAL GRANULAR AND A 

 PERIPHERAL CLEAR ZONE. (Piersol.) 



FIG. 83. SECTION OF HUMAN PAN- 

 CREAS SHOWING, a y a, ISLAND OF 

 LANGERHANS, AND b, THE USUAL ACINI. 

 (Piersol.} 



tissue in which ramify large tortuous capillary blood-vessels. These colum- 

 nar bodies, seen in cross-section in Fig. 83, have been named, after their 

 discoverer, the islands of Langerhans. 



Embryologic investigations have shown that these cells are outgrowths 

 from the primitive acini, to which they remain attached for some time by 

 means of a foot-stalk. This subsequently becomes constricted by the 

 connective tissue and the cells become completely detached. The cells 

 then assume the columnar arrangement, after which vascularization takes 

 place. ^ n 



From the fact that complete extirpation of the pancreas as well as its 

 various diseases is followed by serious disturbances of the carbohydrate 

 metabolism it has been suggested that the islands of Langerhans have a func- 

 tion separate and distinct from that of the glandular portion of the pancreas; 

 that they secrete a specific material which partakes of the nature of an 

 internal secretion which is absorbed by the blood circulating around them 

 and carried to different tissues. The effect on the metabolism of the body 



