CHAPTEE XVII. 



THE URINE. 



THE urine is distinguished from all the other animal fluids by the fact 

 that it represents only the products of the waste or physiological disinte- 

 gration of the body. The living body, while in the active performance 

 of its functions, is the seat of various manifestations of force, such as 

 animal heat, sensibility, and motion, which are the indications of its 

 vitality. These manifestations of force, in the living organism, as well as 

 elsewhere, are only produced at the expense of its materials, and by their 

 change of state or metamorphosis in the internal process of nutrition. 

 It is accordingly an essential condition of the existence and activity of 

 the animal body that it should go through with an incessant transfor- 

 mation and renewal of its component parts. Every living being absorbs 

 more or less constantly certain nutritive materials from without, which 

 are modified by assimilation and converted into the natural ingredients 

 of its tissues. At the same time with this continuous process of growth 

 and supply, there goes on an equally continuous change, by which the 

 elements of the organized frame pass over into new forms of combi- 

 nation, destined to be expelled from the body as the products of its 

 disintegration. 



Certain substances, therefore, are constantly making their appearance 

 in the animal tissues and fluids, which were not introduced with the food, 

 but which have been produced in their interior b} r the process of con- 

 tinued metamorphosis. These substances result from the new combina- 

 tions taking place in the organized frame. They are the forms under 

 which those materials present themselves which have once made part 

 of the animal tissues, but which have become altered by the incessant 

 changes characteristic of living beings, and which are consequently no 

 longer capable of exhibiting vital properties, or of aiding in the per- 

 formance of the vital functions. The process of the elimination and 

 removal of these materials is called excretion, and the materials them- 

 selves are known as the excrementitious substances. 



These substances have peculiar characters by which they are distin- 

 guished from other ingredients of the living body. They are crystal- 

 lizable and for the most part soluble in water, at least in the form under 

 which they appear in the excreted fluids. They are formed in the blood 

 or in the substance of the tissues from which they are absorbed by 

 the blood, and are conveyed by the circulating fluid to the excretory 

 organs through which they are discharged. If their elimination from the 

 body be in any way arrested or impeded, their accumulation in the 

 system produces a disturbance of the vital functions, which is more or 

 (SU) 



