188 



RESPIRATION AND EXCRETION 



Tubule 



Diagram of glomerulus, with 

 connected artery, vein, and end 

 of tubule. 



half inches wide, and one inch in thickness. Its color is dark red. 

 If the structure is examined under the compound microscope, it 

 will be seen to be composed of a vast number of tiny branched 



and twisted tubules. The outer end 

 of each of these tubules opens into the 

 pelvis, the space within the kidney ; the 

 inner end forms a tiny closed sac. In 

 each sac, the outer wall of the tube has 

 grown inward and carried with it a very 

 tiny artery. This artery breaks up 

 into a mass of capillaries. These capil- 

 laries, in turn, unite to form a small vein 

 as they leave the little sac. Each of 

 these sacs with its blood vessels is called 

 a glomer^ulus. 



Wastes given off by the Blood in the 

 Kidney. — In the glomeruli the blood 

 loses by osmosis, through the very thin walls of the capillaries, first 

 a considerable amount of water (amounting to nearly three pints 

 daily) ; second, a nitrogenous waste material known as u'rea; 

 third, salts and other waste organic substances. 



These waste products, together with the water containing them, 

 are known as urine. The total amount of nitrogenous waste leav- 

 ing the body each day is about twenty grams. It is passed through 

 the ure'ters to the u'rinary bladder; from this reservoir it is passed 

 out of the body, through a tube called the ure'thra. After the 

 blood has gone through the glomeruli of the kidneys it is purer 

 than in any other place in the body, because it has lost much of its 

 nitrogenous waste in them and before going to them it gave up 

 a large part of its carbon dioxide in the lungs. So dependent is 

 the body upon the excretion of its poisonous material that in cases 

 where the kidneys do not do their work properly, death may ensue 

 within a few hours. One should drink plenty of water between 

 meals, since urine normally consists of about 96 per cent water 

 and 4 per cent dissolved solids. 



Diet plays a very important part in the care of the kidneys. If 

 we overbalance our diet with too much protein food, we throw 

 increased work on these organs. The nitrogen in proteins cannot 



