347 



CHAPTER X. 



ABSORPTION. 



THE process of absorption lias, for one of its objects, the 

 introduction 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 taking away of parts of the body itself, when, having 

 fulfilled their office, or otherwise requiring removal, they 

 need to be renewed. In both these offices, i.e., in both 

 absorption from without and absorption from within, the 

 process manifests some variety, and a very wide range of 

 action ; and in both it is probable that two sets of vessels 

 are, or may be, concerned, namely, the blood-vessels, and 

 the lacteals or lymphatics, to which the term absorbents 

 has been especially applied. 



Structure and Office of the Lacteal and Lymphatic Vessels and 

 Glands. 



Besides the system of arteries and veins, with their inter- 

 mediate vessels, the capillaries, there is another system of 

 canals in man and other vertebrata, called the lymphatic 

 system, which contains a fluid called lymph. Both these 

 systems of vessels are concerned in absorption. 



The principal vessels of the lymphatic system are, in 

 structure and general appearance, like very small and thin- 

 walled veins, and like them are provided with valves. By 

 one extremity they commence by fine microscopic branches, 

 the lymphatic^ capillaries or lymph- capillaries , in the organs 

 and tissues of nearly every part of the body, and by their 

 other extremities they end directly or indirectly in two 

 trunks which open into the large veins near the heart (fig. 

 92). Their contents, the lymph and. chyle, unlike the blood, 



