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CHAPTEE X. 



ABSORPTION. 



THE process of absorption has, 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. Both these systems of vessels are concerned in 

 absorption. 



The 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 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. 90). 

 Their contents, the lymph and chyle, unlike the blood, pass 

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



