88 ELEMENTARY PHYSIOLOGY. 



being worked over in a manner not well understood, 

 they are capable of further use in the body. Thus 

 we see a wise economy in allowing nothing to go to 

 waste which can in any way be put to further use. 

 This reminds us of the economy practiced in sifting 

 coal ashes taken from our stoves and furnaces, sav- 

 ing therefrom such partly burned coal as may be 

 capable of giving off more heat if put into the fire 

 again. 



The vessels which carry the lymph just 

 lymphatics described are called lymphatics. They 



are more delicate in their structure than 

 the veins and arteries and permeate every part of the 

 body. Wherever blood capillaries are found, there 

 lymph capillaries are also found, though on account 

 of their minute size they can not be seen until injected 

 with mercury or some colored fluid. They vary in 

 number with the variation of the number of blood 

 vessels. 



The functions of the lymphatics of the 



system may be regarded as similar 



m of to those of tiles, or drain pipes, which 

 farmers so frequently lay in wet, 

 swampy lands for the purpose of carrying off the 

 surplus water. The water soaks into these tiles, 

 which carry it off under ground, thus drying the field. 

 Likewise the surplus fluids which collect in all parts 

 of the body are absorbed by the lymphatics the 

 drain pipes of the body which unite, forming 

 larger vessel s, which empty into the thoracic duct, with 

 the contents of which the lymph reaches the heart. 



