80 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



Granules indicating the presence of a zymogen which is called 

 trypsinogen (that is, the precursor of trypsin, the most important 

 ferment of the pancreatic juice) crowd the cells before secretion : 

 these are discharged during secretion, so that in an animal whose 

 pancreas has been powerfully stimulated to secrete, as by the ad- 

 ministration of pilocarpine, the granules are seen only at the free 

 border of the cells (see fig. 21). 



As in the case of gastric juice, experiments on the pancreatic 

 secretion are usually performed with an artificial juice, made by 

 mixing a weak alkaline solution (1-per-cent. sodium carbonate) with 

 an extract of pancreas. The pancreas should be kept some time 

 before the extract is made, so as to ensure that the transformation 

 of trypsinogen into trypsin has taken place. 



FIG. 21. Part of an alveolus of the rabbit's pancreas : A, before discharge; B, after. 

 (From Foster, after Ktthne and Lea.) 



Quantitative analysis of human pancreatic juice gives the following 

 results : 



Water .... 97'6 per cent. 

 Organic solids . . . 1'8 



Inorganic salts . . . 0'6 



Dog's pancreatic juice is considerably richer in solids. 

 The organic substances in pancreatic juice are : 



(a) Ferments. These are the most important both quantitatively 

 and functionally. They are four in number : 



i. Trypsin, a proteolytic ferment. 



ii. Amylopsin or pancreatic diastase, an amylolytic ferment. 



iii. Steapsin, a fat-splitting ferment. 



iv. A milk-curdling ferment. 



(b) A small amount of protein matter, coagulable by heat. 



(c) Traces of leucine, tyrosine, xanthine, and soaps. 



