358 



FOOD AND DIGESTION 



larly 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 fast- 

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

 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. 



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

 structure. (V. D. Harris.) 



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 fer- 

 ments of the gland are developed, and which are therefore a zymogen. In 

 addition to the ordinary alveoli of the pancreas there are distributed irregu- 

 larly in the gland other collections of cells of a different character, the islands 

 of Langerhans. These cells are considerably smaller, their protoplasm is 

 more granular and less easily stained with hematoxylin, and their nuclei are 

 small and stain deeply. The collections of cells vary in size and shape. 

 The islands of Langerhans' cells are not concerned with the production of 

 the pancreatic juice. The special form of nerve terminations, called 

 Pacinian corpuscles, are often found in the pancreas. 



