276 APPLIED PHYSIOLOGY 



These experiments have a very direct bearing on some 

 of the clinical phenomena of contracted kidney. 



The Normal Constituents of the Urine. 



Water. The amount of water excreted in the urine 

 varies greatly, for reasons already considered, and 

 depends also upon the amount of water drunk. In 

 health, however, the quantity in the urine is always 

 greater than that taken in by the mouth. Even although 

 the amount of solids and liquids in the diet be the same, 

 the amount of water excreted varies greatly in the same 

 individual in different circumstances and in different 

 individuals in the same circumstances. This is due to 

 the reciprocal action of the skin and kidneys ; for the 

 greater the amount of the insensible perspiration, the 

 less the amount of water excreted by the kidney, and 

 vice versa. In other words, some individuals have active 

 skins, and others active kidneys. The former excrete 

 a more concentrated urine, and are more prone to suffer 

 from gravel and stone ; the latter, one which is more 

 dilute, and are probably more subject to renal congestion 

 and inflammation. 



The rate at which water is excreted by the kidney 

 probably varies in different persons, but as a rule, if a 

 litre of it be swallowed, it has usually all reappeared in 

 the urine before the lapse of three hours. 



In health the volume of urine excreted by day is 

 much greater than that produced during the night; 

 but in cases of renal disease the quantity of day and 

 night urine is more nearly equal. The reason for this 



