94 NUTRITIONAL PHYSIOLOGY 



constructed. The simplest products of the tryptic process 

 are conveniently called amino-acids. 



The Intestinal Juice. This copious secretion was for- 

 merly regarded as having little to do with digestion. The 

 present disposition is to credit it with a very considerable 

 share. When the pancreatic juice is prevented from enter- 

 ing the intestine it remains possible to keep up the nutri- 

 tion of the animal, and one must conclude that the intes- 

 tinal juice is successfully preparing more than one kind 

 of food for absorption. Samples of the secretion have often 

 been obtained from loops of the intestine disconnected from 

 the remainder of the canal. Different workers give vary- 

 ing accounts of its properties. 



The feature of its digestive action concerning which there 

 is the most general agreement is the hydrolysis of the more 

 complex sugars, the disaccharids. Of these sugars, three 

 are commonly present, and there appear to be three en- 

 zymes adapted to act upon them. Maltose arises princi- 

 pally from the salivary and pancreatic digestion of starch. 

 It is hydrolyzed to dextrose (glucose) by an enzyme, which 

 is best called maltase. Lactose, or milk-sugar, is similarly 

 converted into equal parts of dextrose, and the less familiar 

 sugar galactose by the enzyme lactase. _Saccharose, or 

 cane-sugar, gives rise to dextrose, and a sugar of different 

 properties, levulose (fructose), under the influence of the 

 enzyme, invertase. 



When an extract is prepared from the thoroughly minced 

 lining of the small intestine it can be shown to have the 

 power to cause proteoses and peptones to undergo hydro- 

 lysis, though it is said not to act upon the original unmodi- 

 fied protein. This is equivalent to saying that such an 

 extract can parallel the later work of trypsin, though lack- 

 ing its power to initiate digestion. The enzyme implied 

 has been named erepsin. It is regarded as an open ques- 

 tion whether this enzyme normally enters the cavity of the 

 intestine or does its work within the confines of the cells 

 from which it can be extracted. We may conceive that 

 when an animal is deprived of its pancreatic secretion it is 



