THE DIGESTIVE JUICES 81 



The inorganic substances in pancreatic juice are : 

 Sodium chloride, which is the most abundant, and smaller quanti- 

 ties of potassium chloride, and phosphates of sodium, calcium, and 

 magnesium. The alkalinity of the juice is due to phosphates and 

 carbonates, especially of sodium. 



ACTION OF PANCREATIC JUICE 



The action of pancreatic juice, which is the most powerful and 

 important of all the digestive juices, may be described under the 

 headings of its four ferments. 



1. Action of Trypsin. Trypsin acts like pepsin, but with certain 

 differences, which are as follows : 



(a) It acts in an alkaline, pepsin in an acid medium. 



(b) It acts more rapidly than pepsin ; deutero-proteoses can be 

 detected as intermediate products in the formation of peptone. 

 Primary (i.e. proto- and hetero-) proteoses have not been found ; the 

 action is apparently too rapid to admit of their detection. 



(c) The first degradation product is alkali-albumin in place of the 

 acid-albumin of gastric digestion. 



(d) It acts more powerfully on certain proteins (such as elastin) 

 which are difficult of digestion in gastric juice. Collagen, however, 

 is not digested. 



(e) Acting on solid proteins like fibrin, it eats them away from 

 the surface to the interior ; there is no preliminary swelling as in 

 gastric digestion. 



(/) Trypsin acts further than pepsin, decomposing peptone into 

 simpler products, of which the most familiar are leucine and tyrosine. 



Besides leucine and tyrosine, other amino-acids such as aspartic 

 acid, glutamic acid, lysine, arginine, and tryptophan and ammonia 

 are also formed. A more complete list of the cleavage products with 

 their chemical constitution is given on pp. 31-35. 



We know that the action of proteolytic enzymes is, by the 

 process of hydrolysis, to split the heavy protein molecule into 

 smaller and smaller molecules ; first we get proteoses, then peptones, 

 and finally after prolonged action simple substances like leucine and 

 tyrosine. 



This cleavage is more easily performed by the more powerful 

 tryptic enzyme than by the comparatively feeble agent, pepsin- 

 hydrochloric acid. Still we have already seen that by the very pro- 

 longed action of the latter, leucine, tyrosine, and other amino-acids 



G 



