312 THE ANIMALS AND MAN 



The liver. — This is the largest gland in the body. It 

 lies (fig. 159 Li) beneath the diaphragm, its lobes partly over- 

 lapping the stomach. Its cells, called hepatic cells, secrete 

 bile. Its duct opens into the small intestine near the pyloric 

 end. Unused bile is stored in a small sac or gall bladder con- 

 nected by a duct with the bile duct near its distal end. 



The pancreas (fig. 156). — This gland lies along the 

 curvature of the stomach. Its cells secrete pancreatic 

 juice. Its duct joins the bile duct near its opening into the 

 intestine, so that bile and pancreatic juice intermingle while 

 entering the intestines. 



Digestion in the small intestine. — This is due to the 

 combined action of the three digestive fluids mentioned, 

 intestinal juice, pancreatic juice and hile. 



The intestinal juice furnishes an enzyme that acts upon 

 starches and sugars and upon fats. The pancreatic juice 

 furnishes three enzymes, trypsin, amylopsin, and steapsin. 

 Trypsin, like ptyalin, acts in an alkaline medium. Like 

 pepsin it acts upon proteid converting it into peptone. 

 Amylopsin (diastase), like ptyalin, acts upon starch, con- 

 verting it into sugar. Steapsin (lipase) acts upon fat. Fat 

 is chemically composed of fatty acid and glycerine. This 

 combination must be broken up before fat can be made di- 

 gestible. When once broken up, the fatty acids unite with 

 the alkali present and form a soap which is soluble. This 

 process is saponification. Fat must also be broken up into 

 tiny droplets. This is emulsification. These two processes 

 are accomplished by intestinal juice and steapsin. 



Bile is alkaline and hence serves to neutralize the acid 

 chyme and prepare it for the action of the intestinal and 

 pancreatic juices. It also aids in emulsifying and saponi- 

 fying fats. 



Digestion may be artificially demonstrated as follows. Procure from 

 a druggist some dry pancreatic extract. Dissolve 15 grs. of this in 

 2 oz. of warm water, (i) Half fill a test tube with this artificial digest- 



