158 



THE ESSENTIALS OF HISTOLOGY 



tions, their protoplasm is filled in the inner two-thirds with small 

 granules, but the outer third is left clear (fig. 192, A). After a period of 



FIG. 191. SECTION OF THE PANCREAS OF THE DOG. 



d, termination of a duct in the tubular alveoli, alv. 



a 



B. 



FIG. 19?. PART OF AN ALVEOLUS OF THE RABBIT'S PANCREAS, A, AT REST; 

 B, AFTER ACTIVE SECRETION. (Foster, after Kiihne and Lea.) 



a, the inner granular zone, which in A is larger and more closely studded with fine granules 

 than in B, in which the granules are fewer and coarser ; 6, the outer transparent zone, 

 small in A, larger in B, and in the latter marked with faint strias; c, the lumen, very 

 obvious in , but indistinct in A ; d, an indentation at the junction of two cells, only 

 seen in B. 



activity the clear part of the cell becomes larger, and the granular 

 part smaller (B). In stained sections the outer part is coloured more 

 deeply than the inner. 



In the centre of each acinus there may generally be seen some 

 spindle-shaped cells, the nature of which (whether epithelial or con- 

 nective tissue) has not been determined (centro-acinar cells of Lan- 

 gerhans). 



