664 ELIMINATION OF WASTE PRODUCTS. [BOOK n. 



The lungs serve as the channel for the discharge of the greater 

 part of the carbonic acid, and a considerable quantity of water; 

 this discharge we have just studied. Through the skin there 

 leave the body a comparatively small quantity of salts, a little 

 carbonic acid, and a variable but on the whole large quantity 

 of water. 



The kidneys discharge all or nearly all the urea and allied 

 bodies, the greater portion of the salts, and a large amount of 

 water, with an insignificant quantity of carbonic acid. They are 

 especially important since by them practically all the nitrogenous 

 waste leaves the body, and to them we will turn first. 



