188 THE HUMAN BODY 



ent places. But, receiving in its passage through one re- 

 gion what it loses in another, its average composition is 

 kept pretty constant; and, through interchange with it, the 

 average composition of the lymph also. 



The Lymphatic Vessels or Absorbents. The blood, on 

 the whole, loses more liquid to the lymph through the cap- 

 illary walls than it receives back at the same time. This de- 

 pends mainly on the fact that the pressure on the blood in- 

 side the vessels is greater than that on the lymph outside, 

 and so a certain amount of filtration of liquid from within 

 out occurs through the vascular wall, in addition to the 

 dialysis. The excess is* collected from the various organs 

 of the body into a set of lymphatic vessels, which carry it 

 directly back into some of the larger blood-vessels near 

 where these empty into the heart; and as fast as this on- 

 ward flow of the lymph occurs under pressure from behind, 

 it is renewed in the different organs, fresh liquid filtering 

 through the capillaries to take its place as fast as the old is 

 drained off. 



Since the lymphatic vessels may be said to take up or 

 absorb the excess of liquid drained from the blood and also 

 the effete matters of the various organs, they are frequently 

 called the absorbents. 



Lacteals we have already learned to be only another 

 name for the absorbents of the small intestine (p. 147). 



How is the average composition of the blood maintained? How 

 that of the lymph? 



Give another name for the lymphatic vessels. Does the blood on 

 the whole gain or lose liquid to the lymph as it flows through the cap- 

 illaries ? Explain why. What becomes of the excess of liquid 

 drained off from the blood ? 



Where do the lymphatic vessels convey it? What produces the 

 onward flow of lymph? How is the lymph thus drained off replaced? 

 Why are the lymphatics called absorbents? 



What is meant by the lacteals? 



