90 PHYSIOLOGY CHAP. 



Its most important constituents are the enzymes or soluble 

 ferments. These are usually three ; the diastatic enzyme 

 (amylopsiii), the proteolytic enzyme (trypsiri), and the lipolytic 

 enzyme (steapsin), to which a fourth, on which depends the 

 capacity of the pancreatic juice to coagulate milk (chymosin) 

 should perhaps be added. Pancreatic juice further contains a 

 substance which is precipitated by acetic acid (Halliburton) ; this 

 may be mucin or nucleo-protein. Besides these, xanthme, leucine, 

 fats, soaps, and salts, more especially alkaline chlorides, alkaline and 

 earthy carbonates and phosphates, have also been found. 



Pure trypsin is a protein of unknown composition which in the 

 free state is soluble in water and insoluble in alcohol and 

 anhydrous glycerol, in which, however, it dissolves if -not quite 

 pure. When dissolved in water, the solution being acidulated 

 and boiled, it splits into albumin and peptone (Kiihne). This 

 may, however, be not a true cleavage but a separation, as the 

 albumin may be considered an impurity (Loewi). When dissolved 

 in sodium carbonate and heated to 50 C. its proteolytic activity 

 is destroyed after five minutes : in a neutral solution it is destroyed 

 at 45 (J. ; it is also destroyed by the hydrochloric acid of the 

 gastric juice. Its digestive activity for proteins is best developed 

 in the presence of a 1 per cent solution of sodium carbonate, at a 

 temperature of 40 C. 



The formation of trypsin in the pancreas has been more 

 closely studied than that of any other enzyme. If from a dog 

 that has fasted for 24 hours a glycerol extract of half the 

 pancreas is made immediately after the death of the animal 

 (extract 1), and of the other half when it has been left 24 hours 

 in the air at a temperature of 40 C. (extract 2) taking in both 

 cases one part by weight of the pancreas (ground up with 

 powdered glass) and ten of glycerol, adding to both extracts a 

 1-2 per cent soda solution it is regularly found that the first 

 extract has little or no digestive action upon fibrin, while the 

 second extract has a marked action. This experiment shows 

 that the fresh pancreas contains little or no trypsin, but that it 

 does contain a substance that can be transformed into trypsin, 

 which Heidenhain termed trypsin -zymogen (also known as 

 trypsinogen or protrypsin). 



This zymogen is insoluble in water. Its conversion into 

 trypsin is arrested or greatly hindered by the addition of a 1-2 

 per cent soda solution. But if the glycerol extract containing 

 zymogen is dissolved in sodium carbonate (1-2 per cent), and 

 oxygen passed through it for ten minutes, it becomes strongly 

 active by conversion of the zymogen into the enzyme. Zymogen 

 dissolved in distilled water that has been previously boiled 

 remains inactive ; in unboiled distilled water it becomes active 

 owing to the contained oxygen. The same transformation occurs 



