THE DIGESTIVE SYSTEM 



99 



other comparatively simple products of protein digestion. Amy- 

 lopsin, or diastase, acts on the. starchy constituents of the food in 

 much the same way as does the ptyalin of the saliva, converting 

 them into dextrins and sugars. Steapsin, or lipase, derives its 

 name from the fact that it splits the fats by hydrolysis into 

 glycerin and their fatty acids. These fatty acids combine with 

 the alkaline salts to form a soapy emulsion (Fig. 30). 





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Fig. 30. — Four curves of the secretion of the pancreatic juice, the three in 

 black, from Walter, showing the secretion in dogs on different diets: (1) on 600 

 c.c. of milk; (2) on 250 grams bread; (3) on 100 grams of meat. The curve in red, 

 from Glaessner, shows the secretion in man on a mixed diet, soup, meat, and 

 bread. The figures, 1, 2, 3, etc., along the abscissa indicate hours after the 

 beginning of the meal. The figures along the ordinates indicate the quantity of 

 the secretion in cubic centimeters. (Howell's Physiology.) 



Intestinal juice is secreted by the glands in the intestinal walls, 

 so has been termed succus entericus. It is a light yellow 

 fluid, alkaline in reaction, and contains several enzymes of much 

 importance to the welfare of the animal. These enzymes include 

 erepsin, which is the last agent to act on the products of protein 

 digestion and to prepare them for absorption; diastase, which 

 converts starch into maltose; invertase, which has the power to 

 invert dextrose, maltose, and lactose into the simpler glucose — 



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