CHAPTER VIII. 



ABSORPTION. 



THE process of Absorption has, for one of its objects, the introduc- 

 tion into the blood of fresh materials from the food and air, and of 

 whatever comes into contact with the external or internal surfaces of the 

 body; and, for another, the gradual removal of parts of the body itself, 

 when they need to be renewed. In absorption from without and absorp- 

 tion from within, the process manifests some variety, and a very wide 

 range of action; and in both two sets of vessels are, or may be, con- 

 cerned, namely, the Blood-vessels, and the Lymph-vessels or Lymphatics 

 to which the term Absorbents has been specially applied. 



Lymphatic Vessels. 



Distribution. The principal vessels of the lymphatic system are, in 

 structure and general appearance, like very small and thin-walled veins. 

 They are provided with valves."* They commence in fine microscopic 

 lymph-capillaries, in the organs and tissues of the body, and they end 

 directly or indirectly in two trunks which open into the large veins near 

 the heart (Fig. 314). The lymph and chyle which they contain, unlike 

 the blood, pass only in one direction, namely, from the fine branches to 

 the trunk and so to the large veins, on entering which they are mingled 

 with the stream of blood, and form part of its constituents. Kemem- 

 bering the course of the fluid in the lymphatic vessels, viz.* its passage 

 in the direction only towards the large veins in the neighborhood of the 

 heart, it will readily be seen from Fig. 214 that the greater part of the 

 contents of the lymphatic system of vessels passes through a compara- 

 tively large trunk called the thoracic duct, which finally empties its 

 contents into the blood-stream, at the junction of the internal jugular 

 and subclavian veins of the left side. There is a smaller duct on the 

 right side. The lymphatic vessels of the intestinal canal are called lac- 

 teals, because during digestion, the fluid contained in them resembles 

 milk in appearance; and the lymph in the lacteals during the period of 

 digestion is called chyle. There is no essential distinction, however, 

 between lacteals and lymphatics. In some parts of their course all 

 lymphatic vessels pass through certain bodies called lymphatic glands. 



