CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 405 



normal state, capable of secreting vigorously. It is possible under 

 these circumstances to observe even minutely the appearances 

 presented by the gland when at rest and loaded, and to watch the 

 changes which take place during secretion. 



When the animal has not been digesting for some little time, 

 and the gland is therefore " loaded," the outlines of the individual 

 cells, as we have already said, 220, are very indistinct, the lumen 

 of the alveolus is invisible or very inconspicuous, and each cell is 

 crowded with small, refractive spherical granules, forming an 

 irregular granular mass which hides the nucleus and leaves only 

 a very narrow clear outer zone next to the basement membrane, or 

 it may be hardly any such zone at all. Fig. 63 A. 



The blood-supply moreover is scanty, the small arteries being 

 constricted and the capillaries imperfectly filled with corpuscles. 



If, however, the same pancreas be examined while it is in a 

 state of activity, either from the presence of food in the stomach, 

 or from the injection of some stimulating drug, such as pilocarpin, 

 a very different state of things is seen. The individual cells 

 (Fig. 63 B) have become smaller and much more distinct in 



E. 



FIG. 63. 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. 



outline, and the contour of the alveolus which previously was even 

 is now wavy, the basement membrane being indented at the 

 junctions of the cells; also the lumen of the alveolus is now wider 

 and more conspicuous. In each cell the granules have become 

 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 



