282 EXPERIMENTAL GENERAL SCIENCE 



appear to be formed in the liver and left for the kidneys to 

 remove from the blood. The most abundant substance 

 excreted by the kidneys is of course water, but with it are 

 excreted salt, urea, and other substances which are dissolved 

 in it. A single tube, the ureter, leads from each kidney to the 

 bladder where the material is stored until expelled from the 

 body. The ureter leaves the kidney from the concave side 

 and here also enters and leaves the blood supply to these 

 organs. The refuse from the food taken into the alimentary 

 canal cannot properly be considered an excretion. Its reten- 

 tion in the body, however, may be as harmful as the reten- 

 tion of any of the substances ordinarily excreted, since it 

 forms an ideal breeding place for bacteria which of themselves 

 may produce poisons very harmful when absorbed. 



243. Conditions Affecting Excretion. When the kidneys 

 function properly, the nitrogenous waste is excreted as fast as 

 made in the body, but the amount of water excreted depends 

 somewhat upon the temperature to which the body is sub- 

 jected, the amount of moisture in the air, and sometimes on 

 the condition of the nervous system. In warm weather, a 

 large part of the water taken into the body is evaporated 

 from the skin as perspiration, but in winter a larger propor- 

 tion is excreted by way of the kidneys. Since meats and other 

 nitrogenous foods result in wastes that must be eliminated by 

 the kidneys, those suffering from diseases of these organs 

 find it desirable to greatly reduce the proteins in their diet. 

 Since the salts and other wastes excreted by the kidneys are 

 dissolved in water, the need for drinking sufficient water to 

 keep the kidneys flushed out is apparent. 



Practical Exercises 



1. Why do people suffering from kidney trouble find a warm climate 

 desirable? 



