168 MANUAL OF PHYSIOLOGY. 



granular zone of the cells is, the richer in ferment is the glycerin 

 extract made from the gland. But it has been found that if a 

 glycerin extract be rapidly made from an actively secreting ab- 

 solutely fresh gland, i. e., removed from the dead animal while 

 still warm, the extract is found to be quite inert toward proteids, 

 while an extract made from a portion of the same pancreas which 

 has been kept some hours after death is very active ; and a por- 

 tion of the fresh pancreas pounded in a mortar with a little weak 

 acid so as to develop the trypsin in it, acts in an alkaline solu- 

 tion and forms peptone energetically. 



We must therefore conclude that the special proteolytic fer- 

 ment of the pancreas does not exist prior to the period at which 

 the secretion is poured out from the gland cells. 



Although a definite relation seems to exist between the amount 

 of granules in the active cells and the degree of efficacy of the 

 secretion, the ferment does not appear in full force for some time 

 after that the height of the gland activity has been established, 

 and it is likely that the presence of an acid helps in the birth of 

 the ferment. 



It has therefore been assumed that the granules of the gland 

 cells give rise, not to the proteolytic ferment, but to a ferment- 

 producing substance which is called Zymogen. 



So that if we trace the history of the pancreatic proteolytic 

 ferment, we shall find that, so far as this trypsin is concerned, 

 there can be no question as to whether it pre-exists in the blood 

 and is removed thence by the gland or not, because by studying 

 the process we find that the final elaboration of the secretion 

 takes place after it has got into the ducts or the intestinal cavity. 

 Thus the blood gives to the protoplasm of the gland cells nutri- 

 ment. The protoplasm of the cells, by its intrinsic chemical 

 processes, manufactures peculiar granules. These granules give 

 rise, among other things, to zymogen, which in the presence of 

 an acid begets trypsin. 



Pancreatic Digestion. The pancreatic juice is, of all the 

 digestive fluids, the most general solvent. It acts upon the three 

 great classes of food stuffs which require modification to enable 

 them to pass through the barrier that intervenes between the in- 



