92 NUTRITIONAL PHYSIOLOGY 



slight acidity which may exist in the intestine is not likely 

 to prevent this type of digestion from going on to com- 

 pletion. 



Beside acting on starches, the pancreatic juice continues 

 and greatly accelerates the hydrolysis of fats which has 

 been barely begun in the stomach. The enzyme concerned 

 is called steapsin in the older books, but by more recent 

 writers lipase. The immediate products are glycerin and 

 fatty acids. A secondary formation of soaps is a possibil- 

 ity already indicated. When an oil undergoes digestion 

 it breaks up at an early stage into microscopic drops and is 

 said to be emulsified. This subdivision clearly multiplies 

 the surface of contact between the food and the digestive 

 juice, and has an effect corresponding to that of mastication 

 upon solids. It is, thereftire, most helpful to digestion, 

 but it is not to be confused with digestion itself. 



The statement is commonly made that the pancreatic 

 juice continues the work of pepsin upon proteins by virtue 

 of an enzyme called trypsin. While this is approximately 

 true, it calls for a certain qualification. If the juice is 

 carefully collected as it comes from the main duct of the 

 pancreas without being allowed to mingle with other se- 

 cretions or even to touch the lining of the intestine, it is 

 reported that it is usually incapable of hydrolyzing pro- 

 teins. This power it gains in a striking degree when it has 

 been mixed with ever so little of the intestinal juice, the 

 succus entericus, as it is sometimes called. The interaction 

 of the two secretions is described as resulting in the 

 "activating" of the pancreatic juice. The natural infer- 

 ence is that the inactive fluid contains in solution a body, 

 not yet deserving the name of enzyme, but ready to be- 

 come one by a quick transformation. An inactive ante- 

 cedent body of this kind is termed ^.zymogen; in this specific 

 instance, trypsinogen. Acting on the assumption that 

 there is a definite substance in the intestinal juice capable 

 of changing trypsinogen to trypsin, physiologists have 

 given the name of enterokinase to the agent concerned. 



Tryptic digestion differs in characteristic ways from the 



