THE PANCREATIC JUICE 751 



acid, viz. alkaline to such indicators as methyl orange, and acid to such 

 indicators as phenolphthalein. On investigating the action of trypsin out- 

 side the body, it is found that, at any rate as concerns its earlier stages, this 

 ferment is more active in the presence of sodium carbonate. It is usual to 

 make up an artificial digestive mixture by dissolving commercial trypsin in 

 0-2 to 0-3 per cent, sodium carbonate. The optimum amount of sodium 

 carbonate depends on the strength of the solution in trypsin : the more 

 trypsin present the higher is the optimum amount of sodium carbonate. It 

 is stated that, although an alkaline reaction is more advantageous for the 

 earlier stages of tryptic activity, the later stages take place best in a neutral 

 medium. This result is probably due to the fact that trypsin in alkaline 

 medium is extremely unstable so that, when prolonged digestions are carried 

 out, the trypsin would be rapidly destroyed if the medium were strongly 

 alkaline. The destructibility of trypsin, as well as its action, is largely 

 affected by the presence of proteins or their digestion products in solution. 

 Bayliss has adduced evidence to show that, when trypsin acts upon protein, 

 it enters into some form of combination with the protein molecule. This 

 combination protects the trypsin from the destructive action of alkali. The 

 velocity of the reaction, which takes place under the influence of trypsin, 

 gradually diminishes, owing probably to a combination of the trypsin with 

 the products of digestion, e.g. with the peptones or ammo-acids, and its 

 consequent removal from the sphere of action. If by any means the amino- 

 acids be removed the action of the trypsin is renewed. Destruction of the 

 ferment occurs in the intestine itself. If the intestinal contents be collected 

 by means of a fistula at the lower end of the ileum, they show little or no 

 proteolytic activity. Trypsin is therefore an extremely active ferment, 

 which carries out its function of protein hydrolysis at the upper part of the 

 gut and is destroyed before reaching the lower end. 



THE ACTIVATION OF PANCREATIC JUICE 



It was observed by Kiihne that extracts of the fresh pancreas did not 

 develop their full activity for some considerable time, the development 

 being aided by preliminary treatment with a weak acicL When a pancreatic 

 fistula is made according to Pawlow's method, the juice obtained always 

 presents some proteolytic activity. It was shown by Pawlow and Chepo- 

 walnikoff that the development of the activity of the juice was due to the 

 action of a constituent of the succus entericus which they named enteroJcinase, 

 and it has since been found that, if care be taken to avoid contact of the 

 juice with the mucous membrane surrounding the orifice of the duct, it is, 

 when secreted, entirely inactive. The enterokinase acts like a ferment 

 on a body, trypsinogen, present in the juice as secreted, converting this into 

 trypsin. Pawlow therefore called this body the * ferment of ferments.' 



This view of the action of enterokinase has been challenged, especially by Delezenne> 

 according to whom there is an actual combination between the enterokinase and the 

 trypsinogen, trypsin itself being a mixture or combination of the two ^bodies. He 

 compared the reaction to that of the hsemolysins, which, as is well known, involve in 



