288 



THE ORGANS 



189). The zymogen granules are quite large granules and as 

 they are highly refractive stand out distinctly even in the fresh, 

 unstained condition and under low magnification. The relative 



t2d> 



Fig. 188. — Section of Human Pancreas. X112. (KoUiker.) az), Alveoli; a, inter- 

 lobular duct surrounded by interlobular connective tissue; L, islands of Langerhans; v, 

 small vein. 



size of these zones depends upon whether the cell is in the 

 active or resting state (compare Fig. 190, A and B). During rest 

 (fasting) the two zones are of about equal size. During the early 



stages of activity (intestinal 

 digestion) the granules largely 

 disappear and the clear zone 

 occupies almost the entire cell. 

 During the height of digestion 

 the granules are increased in 

 number to such an extent that 

 they almost fill the cell, while 

 after prolonged secretion they 

 are again almost absent. The 

 cell now returns to the resting 

 state in which the two zones 

 are about equal. The in- 

 crease and disappearance of 

 the granules are marked by the appearance of the fluid secretion of 

 the gland in the lumen. It would thus seem probable that the 

 zymogen granules are the intracellular representatives of the secre- 

 tion of the gland. 



^t^ 







:^- — 



— a 



/^^l^" 



Fig. iSq. — From Section of Human Pancreas. 

 Xyoo. (Kolliker.) a, Gland cell; 6, basement 

 membrane; 5, intermediate tubule; c, centro- 

 acinar cells; sk, intracellular secretory tubule. 



