332 



FOOD AND DIGESTION 



The Pancreas. The pancreas is situated within the curve formed 

 by the duodenum; and its main duct opens into that part of the small intestine 

 through a duct common to it and to the liver and about two and a half inches 

 from the pylorus. 



The pancreas bears some resemblence in structure to the salivary glands. 

 Its capsule and septa, as well as the blood-vessels and lymphatics, are similarly 

 distributed. It is, however, looser, the lobes and lobules being less compactly 

 arranged. 



Heidenhain has observed that the alveolar cells in the pancreas of a fasting 

 dog consist of two zones, an inner or central zone which is finely granular, 



FIG. 266. Section of the Pancreas of Armadillo, Showing the Two Kinds of Gland- structure. 



(V. D. Harris.) 



and which stains feebly, and a smaller parietal zone of finely striated proto- 

 plasm which stains easily. The nucleus is partly in one, partly in the other 

 zone. During secretion it is found that the outer zone increases in size, and 

 the central granular zone diminishes, as in the case of the salivary glands. 

 The pancreatic cell itself becomes smaller from the discharge of the secretion. 

 During a period of rest the granular zone again increases in size and the 

 outlines of the cells become full and indistinct. The granules, as in the sali- 

 vary cells, are the material from which, under certain conditions, the ferments 

 of the gland are developed, and which are therefore a Zymogen. In addition to 

 the ordinary alveoli of the pancreas there are distributed irregularly in the 

 gland other collections of cells of a different character, the Islands oj Lan- 

 gerhans. These cells are considerably smaller, their protoplasm is more 



