198 ANATOMY FOB, NURSES. [CHAP. XVI. 



There are two paths by means of which the products of diges- 

 tion find their way into the blood : (1) by the capillaries in the 

 walls of the stomach and intestines ; and (2) by the lymphatics 

 in the walls of the small intestine (the lacteals). 



(1) The network of capillary blood-vessels is spread, as we 

 have seen (page 168), immediately beneath the basement mem- 

 brane of the mucous coat lining the interior of the alimentary 

 canal, and matters in solution pass readily by diffusion or osmo- 

 sis from the interior of the stomach and intestines into the 

 blood-vessels in their walls. All the blood from the digestive 

 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 (dextrose or glucose). Thus the liver is a very com- 

 plex organ whose cells elaborate bile and glycogen, and by 

 some ferment-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 



