CHAPTER XVII. 

 THE KIDNEYS AND THEIR FUNCTION. 



1. Why the Kidneys are Needed. We have seen how 

 the body gets rid of one of its chief waste matters, 

 namely, carbonic acid. Another waste substance is 

 formed in it every day in large quantity, and if not car- 

 ried out would do just as much harm as carbonic acid. 

 This waste substance is named urea. It is solid, and so 

 cannot be separated by the lungs, which can pass out 

 gases and vapors. The urea is removed by the kidneys, 

 along with a great deal of water in which it is dissolved; 

 it is thus passed out in a liquid form. 



Urea contains nitrogen, and is produced when albu- 

 mens are oxidized (p. 83), or used up, in doing their 

 work in the body. 



2. The Renal Organs include not merely the kidneys, 

 but the apparatus by which their secretion is carried to 

 the outside of the body and expelled from it. They are: 



(1) the kidneys, two large glands placed in the abdomen; 



(2) the ureters, or the ducts (p. 66), of the kidneys, which 

 carry the secretion to (3) a reservoir, the bladder, where 

 it collects. The bladder is a muscular bag. It contracts 



1. What is urea? Why can it not be separated by the lungs? 

 What organs remove it ? In what form ? What does urea contain ? 

 How is it produced ? 



2. What do the renal organs include? Name them. Function of 

 ureters? Of bladder? Of urethra? When do the kidneys work ? 



