PANCREATIC DIGESTION 61 



activity reveals changes comparable to those akeady described in the 

 case of salivary and gastric cells. Granules indicating the presence of 

 a zymogen which is called trypsinogen (that is, the precui-sor 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 administration 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 



Fig. 21.— Part of an alveolus of the rabbit's pancreas : A, before discbarge ; B, after. 

 (From Foster, after Kiihne and Lea.) 



before the extract is made, or treated with dilute acid so as to ensure 

 that the transformation of tr}^sinogen into trypsin has taken place. 



Quantitative analysis of human pancreatic juice gives the following 

 results : — 



Water .... 976 per cent. 

 Organic soHds . . . 1-8 „ 

 Inorganic salts . . . 06 „ 



Dog's pancreatic juice is considerably richer in solids. 



The organic substances in pancreatic juice are — 



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

 and functionally. They are four in number : — 



i. Trypsin, a proteol}i)ic ferment. 



ii. Amylopsin or pancreatic diastase, an amylolytic ferment. 



iii. Steapsin, a fat-splitting ferment. 



iv. A milk-curdling ferment. 



(&) k small amount of proteid matter, coagulable by heat. 



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



