DIGESTION. 



99 



zones viz., an outer parietal zone, which is transparent and apparently homo- 

 geneous, staining rapidly with carmin; an inner zone, which borders the lumen, 

 and is distinctly granular and stains but slightly with carmin. These cells 

 undergo changes similar to those exhibited by the cells of the salivary glands 

 during and after active secretion. As soon as the secretory activity of the 

 pancreas is established, the granules disappear, and the inner granular layer 

 becomes reduced to a very narrow border, while the outer zone increases 

 in size and occupies nearly the entire cell. During the intervals of secre- 

 tion, however, the granular layer reappears and increases in size until the 

 outer zone is reduced to a minimum. It would seem that the granular 

 matter is formed by the nutritive processes occurring in the gland during 

 rest, and is discharged during secretory activity into the ducts, and takes part 

 in the formation of the pancreatic secretion. 



Towards the outer extremity of the pancreas there are found among the 

 acini collections of globular cells arranged in rods or columns separated by 

 connective tissue. They have been termed after their discoverer, the Islands 

 of Langerhans. It is believed they produce an internal secretion which 

 in some way regulates sugar metabolism. 



The pancreatic juice is transparent, colorless, strongly alkaline, and viscid, 

 and has a specific gravity of 1040. It is one of the most important of the 

 digestive fluids, as it exerts a transforming influence upon all classes of 

 alimentary principles, and has been shown to contain at least three distinct 

 ferments. It has the following composition: 



COMPOSITION OF PANCREATIC JUICE. 



Water 900.76 



Protein material 90 .44 



Inorganic salts 8 . 80 



1,000.00 



The pancreatic juice is characterized by its action: 



1. Upon starch. When starch is subjected to the action of the juice, it is 

 at once transformed into maltose; the change takes place more rapidly 

 than when saliva is added. This action is caused by the presence of a 

 special ferment, amylopsin. 



2. Upon protein. The protein bodies which escape digestion in the stomach 

 are converted into peptones by the action of the alkali and ferment. 

 The first effect of the alkali is to change the protein into an alkali-protein, 

 a fact which indicates that in the digestion of protein by pancreatic juice, 

 the first stage is alkalinization. This having been accomplished, the fer- 

 ment trypsin transforms the alkali-albumin into peptone. For the same 



