THE DIGESTIVE SYSTEM 



289 



In sections of the gland there are seen within the lumina of many 

 of the secreting tubules one or more small cells of which little but the 

 nucleus can usually be made out. These cells lie in contact with the 

 secreting cells, and resemble the flat cells which line the intermediate 



•a 



£. 



FiG. igo. — Sections of Alveoli from Rabbit's Pancreas. (Foster, after Kiihne and 

 Lea.) A, Resting alveolus, the inner zone (a), containing zj'mogen granules, occupying 

 a little more of the cell than the outer clear zone (b); c, indistinct lumen. B, Active 

 alveolus, granules coarser, fewer, and confined to inner ends of the cell (a), the outer 

 clear zone (b) being much larger; outlines of cells and of- lumen much more distinct. 



tubule. They are known as the centra- acinar {centro-tuhular) cells of 

 Langerhans (Fig. 189, c). Their significance is not definitely known. 

 Langerhans beheved that they were derived from the intermediate 

 tubule, the epithelium of which, instead of directly joining that of 



Fig. iqi. — Sections through Alveoli of Human Pancreas — Golgi Method — (Dogiel), 

 to show intracellular secretory tubules, a, Intermediate tubule giving off several 

 terminal tubules, from which pass off minute intracellular secretory tubules; b, gland 

 cells hning terminal tubules. 



the terminal tubule as in the submaxillary gland, was continued over 

 into the lumen of the terminal tubule (Fig. 189). This interpretation 

 has been quite generally accepted. 



Cells which differ from the secreting cells are frequently found 



19 



