176 ANATOMY FOE, NUKSES. [CHAP. XV. 



tive organs is taken by the portal vein to the liver, and the 

 products of digestion are modified by the action of the liver 

 before they are returned to the general circulation by the 

 hepatic veins. The hepatic veins pour their contents into the 

 inferior vena cava, and the blood, enriched with the products of 

 digestion, finally finds its way into the right side of the heart, 

 whence it is taken to the lungs for purification before being 

 sent to all parts of the body. 



During the passage of the blood through the liver, the liver- 

 cells not only take from it the material they need to form 

 the bile ; they also take from it material to form a starchy sub- 

 stance, called glycogen. This glycogen, stored in the liver-cells, 

 is gradually doled out, as it is needed, to the blood. It is not 

 doled out, however, in the form of glycogen, which closely 

 resembles starch, and is, therefore, insoluble, but in the form 

 of sugar or glucose. Thus the liver is a very complex organ 

 whose cells elaborate bile and glycogen, and by some fer- 

 ment-body, contained within themselves, convert the glycogen 

 into glucose. 



(2) Matters in solution can pass into the blood-vessels, but 

 some other provision is necessary for the absorption of the 

 emulsified fats. We find, accordingly, in the villi, which so 

 closely cover the internal surface of the small intestine, little 

 rootlets or beginnings of lymphatic vessels, which are set apart 

 for the absorption of the fatty products of digestion. 



These lymphatic rootlets or lacteals, as they are generally 

 called, occupy the centre of each villus. The emulsified fats 

 pass, probably aided by the bile, into the bodies of the columnar 

 cells on the surface of the villi, and from thence find their way 

 into the interior of the villus, and finally into the beginning of 

 the lacteal. 1 The lacteals carry this fatty matter or chyle to 

 the larger lymphatics in the mesentery, and these empty their 

 contents into the thoracic duct which opens into the great veins 

 on the right side of the neck. 



1 It is supposed that the fat gets into the interior of the lacteals mainly by 

 the action of the leucocytes or lymph corpuscles. First, the fat is taken up by 

 the epithelium cells on the surface of the villus, and, after passing through them, 

 is taken up by the leucocytes ; next, the leucocytes migrate, carrying the fat 

 particles by their amoeboid movements into the lacteal ; and finally, after enter- 

 ing the lacteal, they dissolve or break up and set the fat particles free. 



