DIGESTION 321 



certain part of the maltose into dextrose. It acts best in a 

 faintly acid medium. 



3rd A Lipase or Fat-splitthig Enzyme.— This is the 

 most easily destroyed and the most difficult to separate of 

 the enzymes. It breaks the fats into their component glycerol 

 and fatty acids. The fatty acids link with the alkalies which 

 are present to form soaps, and in this form, or dissolved as 

 free fatty acids in the bile, they are absorbed. 



But the formation of soaps also assists the digestion of 

 fats by reducing them to a state of finely divided particles, 

 an emulsion, upon which the lipase can act more freely. 

 This process of emulsitication is assisted by the presence of 

 proteins in the pancreatic juice and also by the presence of 

 bile. 



UJi. It is doubtful whether the pancreatic secretion 

 contains rennin apart from trypsin, although it produces a 

 modified clotting of milk, under certain conditions. 



That these enzymes are independent of one another is 

 shown by the facts that one may be present without the 

 other, e.g. diastase is absent in man in early childhood ; and 

 also that diastase may be in an active state while the trypsin 

 is in its inactive trypsinogen state. 



As to the mode of production of these enzymes, it is known 

 that trypsin is not formed as such in the cells, for the 

 secretion, direct from the acini, has no tryptic action. A 

 forerunner of trypsin — trypsinogen — is produced, and this 

 changes into trypsin after it is secreted. The intestinal 

 secretion contains a substance of the nature of an enzyme, 

 enterokinase, which has the power of bringing about this 

 change of trypsinogen to trypsin, thus activating it (fig. 154). 



3. Physiology of Pancreatic Secretion. — (a) Chemical 

 Control. — The secretion of pancreatic juice is not constant, 

 but is induced when the acid chyme passes into the duo- 

 denum. This occurs, even when all the nerves to the 

 intestine have been cut, and it appears, from the investiga- 

 tions of Bayliss and Starling, to be due to the formation of 

 a material, which has been called secretin, in the epithelium 

 21 



