254 A MANUAL OF VETERINARY PHYSIOLOGY 



membrane of the intestinal canal. A ferment acting on a 

 ferment has been described as a kinase, and as this one is derived 

 from the bowel it is called enterokinase, a very small amount of 

 which is capable of converting inactive trypsinogen into active 

 trypsin. It is remarkable that of the three ferments secreted 

 by the pancreas, trypsin is the only one which is secreted in an 

 inactive condition. Pawlow considers this to be due to the fact 

 that if trypsin were active in the pancreatic juice, it would 

 destroy its fellow-ferments, but that in the bowel these ferments 

 are protected. 



The fact that extracts of pancreas, as obtained usually from a 

 slaughter-house, may be made more tryptically active by the 

 addition of a little dilute acetic acid, does not now imply that 

 the acid has converted the trypsinogen into trypsin, as has usually 

 been supposed. The pancreas used in the preparation of the 

 extracts is already contaminated with minute quantities of 

 enterokinase, whose activity is greatly increased by neutralising 

 the alkalinity of the extracts. If a pancreas be obtained under 

 conditions which insure the absence of any admixture with even 

 traces of enterokinase, extracts of such a pancreas cannot be 

 rendered more tryptically active by the addition of dilute acid 

 (Starling). It is now believed that the conversion of inactive 

 to active trypsin may be effected by salts of calcium and 

 magnesium, as well as by enterokinase. 



The action of trypsin on proteins is most interesting. The 

 protein molecule is very complex ; the use of trypsin is to split 

 it up into simpler products, with the object of facilitating its 

 absorption. As we shall point out later, no food substance is 

 taken up excepting in its simpler form, and the proteins of oats, 

 barley, hay, or flesh, have to be reconstructed in order to form 

 part of the tissues of the living animal. To enable this to be 

 done trypsin acts on the large protein molecule, and breaks it 

 down in the production of a number of simpler bodies of smaller 

 molecular weight ; on these the tissue-cells set to work, and by a 

 process of synthesis construct the form of protein needed by the 

 body. It can be easily shown that the action of trypsin on 

 protein is much more satisfactory and thorough if the latter has 

 previously been acted upon by pepsin. Trypsin, like pepsin, 

 produces albumose and peptones ; but the process does not stop 

 at peptone ; no peptone can be found in the blood, and none 

 remains after a prolonged pancreatic digestion. The action of 

 trypsin on proteins is nearly as complete as boiling protein with 

 acid. In each case the hydrolysis results in the production of a 

 large number of simpler end-products, chiefly of amino-bodies. 

 Yet it would appear clear that the products obtained by acid 

 hydrolysis are not quite the same as those produced by tryptic 



