452 



THE URINE. 



From these proportions, however, most of the consti- 

 tuents are, even in health, liable to variations. Especially 

 the water is so. Its variations in different seasons, and 

 according to the quantity of drink and exercise, have 

 already been mentioned. It is also liable to be influenced 

 by the condition of the nervous system, being sometimes 

 greatly increased in hysteria, and some other nervous 

 affections; and at other times diminished. In some 

 diseases it is enormously increased ; and its increase may 

 be either attended with an augmented quantity of solid 

 matter, as in ordinary diabetes, or may be nearly the sole 

 change, as in the affection termed diabetes insipidus. In 

 other diseases, e.g., the various forms of albuminuria, the 

 quantity may be considerably diminished. A febrile con- 

 dition almost always diminishes the quantity of water; 

 and a like diminution is caused by any affection which 

 draws off a large quantity of fluid from the body through 

 any other channel than that of the kidneys, e.cj.^ the bowels 

 and the skin. 



Urea. Urea is the prin- 

 cipal solid constituent of the 

 urine, forming nearly one- 

 half of the whole quantity of 

 solid matter. It is also the 

 most important ingredient, 

 since it is the chief substance 

 by which the nitrogen of de- 

 composed tissue and super- 

 fluous food is excreted from 

 the body. For its removal, 

 the secretion of urine seems 



especially provided ; and by its retention in the blood the 

 most pernicious effects are produced. 



Urea, like the other solid constituents of the urine, 



126.= 



Fig. 126. Crystals of urea. 



