THE EXCRETORY SYSTEM. 97 



plainly shown by the Anatomical Aid (manikin of 

 the body). These dark-colored little glands have a 

 very important function to perform. They cannot 

 delegate their work to any other organ of the body, 

 as is the case with some of the other glands. They 

 alone can perform the work assigned them. Hence, 

 when diseased, their work is not done, and sickness 

 ensues. 



The particular and only work of the 



Work of the i i P 111 



Kidneys. kidneys is to separate from the blood 

 brought to them, a substance called 

 urea. This is a very poisonous matter, which, if 

 not removed from the body by the healthy action of 

 the kidneys, will accumulate, and finally cause 

 death. 



The renal arteries (g) constantly carry 



The Kidneys . , . .. V / , , i 



at work. to the kidneys a portion of the blood, 

 which passes through the capillaries of 

 the kidneys, as seen by turning back the first sec- 

 tion of the right kidney of the manikin. The 

 blood is again collected by the veins, and conveyed 

 through the renal vein (h) to the large veins lead- 

 ing to the heart. In the capillaries of the kidneys 

 the blood loses its watery part, which carries, in so- 

 lution, impurities called urea. This watery fluid 

 soaks through the thin capillary walls, is collected 

 and conveyed by two tubes (56), called ureters, to 

 the bladder (57), whence it is expelled from the 

 body. 



