758 



PHYSIOLOGY 



present two well-marked zones, a narrow peripheral zone in which the 

 nucleus is embedded, which is strongly basophile, and a central part which 

 is turned towards the lumen, occupying two-thirds or three-quarters of the 

 cell, and is closely packed with highly refractive granules strongly acidophile 

 and presumably containing or composed of the precursors of the various 

 constituents of the pancreatic juice (Fig. 353). If the activity of the gland 

 be aroused by injection of secretin and the injection be continued until the 



B 



Fia. 353. Alveoli of dog's pancreas. (BABKIN, RTTBASCHKIN and SAWITSCH.) 

 A, resting ; B, after moderate secretion with discharge of granules. 



rate of secretion evoked by each injection diminishes considerably, i. e. the 

 gland shows signs of fatigue, marked changes are observed both macro- 

 scopically and under the microscope. The gland is now pink and trans- 

 parent in appearance, moist and soft in consistence. On section the lumen 

 of each alveolus is enlarged, the cells are shrunken, and the granules are 

 found to lie only along the border of the cell turned towards the lumen, the 

 rest of the cell, which is much reduced in size, being made up of the 

 basophile protoplasm. Similar effects are observed after long continued 

 stimulation of the vagus (Fig. 353 B). 



