THE KIDNEYS AND SKIN. 



433 



Normal urine consists, in 1000 parts, of about 960 water 

 and 40 solids. The latter are mainly crystalline nitrogenous 

 bodies (urea and uric acid], but small quantities of pigments 

 and of non-nitrogenous organic bodies are also present, and a 

 considerable quantity of mineral salts. The following table 

 gives approximately, in the first column, the average compo- 

 sition of the urine excreted in twenty-four hours expressed im 

 grams; in the second column the same expressed in grains. 

 The third column gives the composition of 1000 parts of 

 urine. 



The urine, however, even in health is subject to consid- 

 erable variation in composition; not only as regards the 

 amount of water in it, but also in respect to its solid con- 

 stituents; the latter are especially modified by the quantity 

 and nature of the food taken. 



The Crystalline Nitrogenous Constituents of the Urine 

 are of great interest as they represent the final result of the 

 breaking down in the Body of albuminous and gelatinaginous 

 substances, whether due to tissue waste or to the destruction 

 in the bodily liquids of proteids and albuminoids existing in 

 them in solution. Their chemical relationships tend to cast 

 some light on the structure of an albumen molecule and on 

 the metabolisms it undergoes in the living organism. 



