712 



PHYSIOLOGY 



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 con- 



FIG. 341. Alveoli of dog's pancreas. (BABKIN, RUBASCHKIN and SAWITSCH. ) 

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



stituents of the pancreatic juice (Fig. 341). If the activity of the gland be 

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

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

 shows signs of fatigue, marked changes are observed both macroscopically 

 and under the microscope. The gland is now pink and transparent in appear- 

 ance, 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. 341 B). 



