DIGESTION. 



99 



granules and the lumen is almost invisible. When active, the cells 

 first swell up and press outward against the basement membrane: 

 later they diminish in size as the granules pass out through tho 

 now opened lumen, and so leave a large, clear zone. The presence 

 of these numerous small granules marks the presence, in the cells, 

 of a zymogen, termed trypsinogen, which is the precursor of trypsin, 

 the active ferment of the pancreatic juice. In the interalveolar 

 tissue are islets of small cells permeated with a close network of 

 convoluted capillaries. These cells are also met with in the carotid 

 and coccygeal glands. In the pancreas they are called cells of 

 Langerhans, and are often degenerated in pancreatic diabetes. 



A B 



Fig. 26. Pancreas of Rabbit Observed During Life. (KuHNE and 

 LEA.) (From Tigerstedt's "Human Physiology," copyright, 1906, by D. 

 Appleton and Company. ) 



A, Resting gland. B, Secreting gland. 



The pancreatic blood-vessels are derived from the splenic and 

 branches of the hepatic and superior mesenteric. Its nervous supply 

 comprises networks of fibers from the splenic plexus. 



Pancreatic Secretion (Pawlow). 



Each kind of food determines the secretion of a definite quan- 

 tity of pancreatic juice, while the result as regards ferments is truly 

 striking. The greatest amount of proteid ferment is found in 

 "milk-juice," less in "bread-juice" and "flesh-juice." The most 

 amylolytic ferment occurs in "bread-juice," less in "milk-juice" and 

 "flesh-juice." On the other hand, "bread-juice" is extraordinarily 



