CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 341 



much fewer in number and as it were have retreated to the inner 

 margin, so that the inner granular zone is much narrower and the 

 outer transparent zone much broader than before ; the latter too 

 is frequently marked at its inner part by delicate striae running 

 into the inner zone. At the same time the blood vessels are 



FIG. 77. A PORTION OF THE PANCREAS OF THE RABBIT. (Kiihne and Sheridan Lea). 

 A at rest, B in a state of activity. 



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. 



b the outer transparent zone, small in A, larger in B, and in the latter marked 

 with faint striae. 



c the lumen, very obvious in B, but indistinct in A. 



d an indentation at the junction of two cells, seen in B, but not occurring in A. 



largely dilated and the stream of blood through the capillaries is 

 full and rapid. 



With care the change from the one state of things to the other 

 may be watched under the microscope. The vascular changes can 

 of course be easily appreciated, but the granules may also be seen 

 to diminish in number. Those at the inner margin seem to be 

 discharged into the lumen, and those nearer the outer margin 

 to travel inwards through the cell-substance towards the lumen, 

 the faint striae spoken of above, apparently at all events, being the 

 marks of their paths. Obviously during secretion, the granules 

 with which the cell-substance was ' loaded ' are ' discharged * from 

 the cell into the lumen of the alveolus. What changes these 

 granules may undergo during the discharge we shall consider 

 presently. 



Sections of th, prepared and hardened pancreas of any animal 

 tell nearly the same tale as that thus told by the living pancreas 

 of the rabbit. In sections for instance of the pancreas of a dog 

 which has not been fed, and therefore has not been digesting, for 

 some hours (24 or 30), the cells are seen to be crowded with 

 granules (which however are usually shrunken and irregular owing 

 to the influence of the hardening agent), leaving a very narrow 

 outer zone. In similar sections of the pancreas of a dog which 

 has been recently fed, six hours before for example, and in which 



