178 PHYSIOLOGY. 



other veins, the portal vein divides and subdivides, forming 

 capillaries which ramify through the liver. The blood is 

 again collected by veins, forming the hepatic vein which 

 empties into the postcaval vein close to the diaphragm. 

 From the blood the liver manufactures at least two impor- 

 tant substances, the bile and liver starch, or glycogen. 



Functions of Bile. The bile is secreted all the time, 

 but more actively during digestion. The part made while 

 digestion is not going on is stored in the bile sac. The 

 functions of the bile are still poorly understood. But the 

 following are believed to be a part of its work : 



1. It is believed to aid in emulsifying the fats. 



2. It is supposed to aid in the absorption of fat. 



3. The bile, to a certain extent, is waste matter ; so the 

 liver is an organ of excretion as well as an organ of secretion. 



4. It is found that if, for any cause, the bile is prevented 

 from entering the intestine, constipation follows, and the 

 contents of the "large intestine have a much more fetid 

 odor than usual. The bile itself readily putrefies; hence 

 it is concluded that the bile has no positive antiseptic 

 properties, but in some indirect way retards putrefaction. 



The liver, from its size, ought certainly to be of great 

 importance in the body; it is the largest gland in the 

 body, and receives one fourth of the blood. 



The Work of the Pancreatic Juice. The pancreatic 

 juice acts on all the principal classes of foodstuffs : 



1. A ferment in it called amylopsin acts on starches, 

 changing them to sugar, even more energetically than the 

 ptyalin of the saliva. 



2. Another constituent of pancreatic juice is trypsin ; 

 like the pepsin of gastric juice, this ferment has the power 

 of changing proteids to peptones. 



