DIGESTION 331 



acidity of the gastric juice when titrated against standard 

 alkali. The quantity of pancreatic juice secreted during the 

 twenty-four hours in an average man has been estimated at 

 500 to 800 c.c. from observations on cases of fistula. Probably 

 under perfectly normal conditions it is greater. A so-called 

 artificial pancreatic juice can be made by extracting the pancreas 

 with water or glycerin. Since better methods of obtaining the 

 natural juice have been developed, these extracts have lost some 

 of their importance. 



Fresh pancreatic juice contains four ferments : (i) The mother- 

 substance, trypsinogen, of a proteolytic or protein-digesting 

 ferment, trypsin ; (2) an amylolytic ferment, amylopsin ; (3) a 

 fat-splitting or lipolytic ferment, steapsin ; (4) a milk-curdling 

 ferment. It is doubtful whether the last is a different body 

 from the trypsin (see p. 326). In any case, it cannot be con- 

 sidered as taking any practical share in digestion, since it can 

 hardly ever happen that milk passes through the stomach with- 

 out being curdled. 



Trypsinogen has no action upon proteins, but in normal 

 digestion it is changed into active trypsin by the enterokinase 

 of the intestinal juice (p. 343). Pancreatic juice collected with- 

 out contact with intestinal contents or with the mucous mem- 

 brane of the intestine does not digest proteins. The same is 

 true of extracts of perfectly fresh pancreas, but if the pancreas is 

 allowed to stand for a time, the extracts contain active trypsin, 

 perhaps because some decomposition product has activated 

 the trypsinogen. Some writers, however, state that when con- 

 tamination of the gland with intestinal contents or contact with 

 the mucosa has been avoided in its removal from the body, such 

 extracts will remain inactive for months, although the trypsin- 

 ogen can at once be activated to trypsin by the addition of 

 enterokinase. 



Trypsin, to a certain extent, corresponds with pepsin in its 

 action on proteins. But it acts energetically in an alkaline as 

 well as in a not too acid medium (a very slight amount of diges- 

 tion may go on in distilled water) ; and its action, unlike that 

 of pepsin at least in digestions of moderate duration does not 

 stop mainly at the peptone stage, but goes on rapidly to the 

 production of the amino - acids, the basic substances arginin, 

 lysin, and histidin, known as the hexone bases, and most of 

 the other decomposition products obtained by boiling proteins 

 with dilute acids. The most important of these products, so far 

 as they have been isolated and identified, are enumerated in 

 the following table (see also pp. 1-3) : 



