ABSORPTION. 41 



by the efferent vessels and transmitted onward. The lymph corpuscles 

 which are washed out of the gland into the lymph stream are formed, most 

 probably, by division of pre-existing cells. 



The Thoracic Duct is the general trunk of the lymphatic system, into 

 which the vessels of the lower extremities, of the abdominal organs, of the 

 left side of the head and left arm empty their contents. It is about twenty 

 inches in length, arises in the abdomen, opposite the third lumbar vertebra, 

 by a dilatation, \ho. receptaculum chyli ; ascends along the vertebral column 

 to the seventh cervical vertebra, and terminates in the venous system at 

 the junction of the internal jugular and subclavian veins on the left side. 

 The lymphatics of the right side of the head, of the right arm and the right 

 side of the thorax, terminate in the right thoracic duct, about one inch in 

 length, which joins the venous system at the junction of the internal jugular 

 and subclavian on the right side. 



The general arrangement of the lymphatic vessels is shown in Fig. 5. 



The Blood Vessels which are concerned in the conduction of fresh 

 nutritive material from the alimentary canal, have their origin in the elaborate 

 capillary network in the mucous membrane. The small veins which emerge 

 from this network gradually unite, forming larger and larger trunks which 

 are known as the gastric, superior and inferior mesenteric veins. These 

 finally unite to form the portal vein, a short trunk about three inches in 

 length. The portal vein enters the liver at the transverse fissure, after 

 which it forms a fine capillary plexus ramifying throughout the substance 

 of the liver; from this plexus the hepatic veins take their origin, which 

 finally empty the blood into the vena cava inferior. (See Fig. 6.) 



Absorption of Food. Physiological experiments have demonstrated 

 that the agents concerned in the absorption of new materials from the ali- 

 mentary canal are: ist. The blood vessels of the entire canal, but more 

 particularly those uniting to form the portal vein. 2d. The lymphatics 

 coming from the small intestine which converge to empty into the thoracic 

 duct. As a result of the action of the digestive fluids upon the different 

 classes of food stuffs, albumins, sugars, starches and fats, there are formed, 

 peptones, glucose and fatty emulsion, which differ from the former, in being 

 highly diffusible, a condition essential to their absorption. In order that 

 these substances may get into the blood, they must pass through the layer of 

 cylindrical epithelial cells and the underlying basement membrane and into 

 the lymph spaces of the villi and sub-mucous tissue. The mechanism by 

 which the cells effect this passage of the food is but imperfectly understood. 

 D 



