PANCREATIC JUICE 135 



proteins. While capable, like pepsin, of acting upon the 

 native protein, trypsin differs from pepsin in that its 

 action is more complete, for within an hour of tryptic 

 digestion, amino-acids make their appearance. As the 

 result of the action of this ferment, therefore, superadded 

 to that of pepsin, proteins are converted into a mixture 

 of peptones, polypeptides and amino-acids. 



Accompanying the proteolytic action of trypsin, and 

 probably due to the same ferment, there is a transient 

 clotting of milk. 



It appears that trypsin is destroyed in an alkaline fluid 

 of the same degree of alkalinity as the contents of the 

 intestine, but that this destruction is prevented by the 

 products of its own activity. As these are removed by 

 absorption the ferment is killed. 



Amylase. — This enzyme resembles ptyahn in converting 

 starch through the dextrin stage to maltose. 



Lipase. — This ferment in the presence of alkaUes converts 

 fats into glycerine and soaps. It is indeed the principal 

 hpolytic ferment in the body. Since its action is materially 

 influenced by the bile, we shall dicuss it more fully later on. 



Maltase. — In neutral solutions pancreatic juice has some 

 power of converting maltose into dextrose. The degree to 

 which this occurs in the body will therefore depend upon 

 the extent to which the juice is neutrahsed by the acid 

 contents of the stomach. 



The Secretion of Pancreatic Juice 



Although the pancreas receives fibres, both from the 

 vagus and the sympathetic, the amount of secretion which 

 can be obtained by stimulation of either of these nerves 

 is small and uncertain. Shght secretion begins within two 

 minutes of the taking of food — evidently a nervous mechan- 

 ism. But the onset of a full secretion coincides with the 

 first appearance of food in the duodenum. It was shown 

 in Pavlov's laboratory that the actual stimulus was the 

 presence of HCl in that part of the gut, and that the effect 



