THE EXCRETORY SYSTEM. 93 



THE EXCRETORY SYSTEM. 



It will be remembered that the material collected 

 by the lymphatics is principally such as is capable 

 of being worked over in the little workshops, the 

 lymphatic glands, and used again as building mate- 

 rial of the body. 



There is, however, much waste matter which can 

 not be thus elaborated for further use in tissue- 

 building; and yet some of this material is taken 

 from the blood by organs adapted to this particular 

 purpose, and converted into substances essential to 

 some of the vital processes. Other parts are fit for 

 nothing whatever, and must be expelled from the 

 system, because, if allowed to remain in the blood, 

 they would not only be useless, but an actual poison 

 to the system. 



The organs whose function it is to take 



The Excre- 



tory from the blood such substances as can 



^^ ^ Q utilized again in the body -build- 

 ing process, but which must either be changed into 

 some other substance, or expelled from the body, 

 are the lungs, liver, kidneys and skin. Each of 

 these is suited to take from the blood its own kind 

 of impurities, and either elaborate them into some 

 usable substance or start them in their course lead- 

 ing from the body . 



