URINE. — Lat. Urina ; Gr. ra oTpov ; French, l'Urine; Ital. l'Urina; Germ. das Hams.
The urine may be defined as that fluid which is eliminated by the kidneys in the dis charge of their excretory function.
The human urine being that of an omnivo rous feeder, differs materially from that which is excreted by animals purely carnivorous or herbivorous. In cases occasionally met with, however, where, either from congenital taste, want, or the indulgence of eccentricity or curiosity, vegetable food alone has been taken by human beings, the urine has been observed to undergo certain modifications as a conse quence.
The urine, it is obvious, must vary much in constitution, according to the conditions under which the organism is placed, both in respect to external and internal circumstances. Thus the state of the atmosphere, as respects heat and cold, dryness and moisture, will affect the quantity of water excreted, as a constituent of the urine, while the quality and quantity of the ingesta, the state of the chylo poietic organs, and the amount of exertion to which the body has been subjected, are all causes tending to modify the amount, and perhaps also the nature and quality, of the solid matters excreted by the kidneys.
When treating, therefore, of the chemistry of normal urine, it must be borne in mind that, in fixing a standard, we are but giving a result more or less approaching to the truth, and that the real method of obtaining a philo sophical view of its chemical constitution is, to regard the urine in its variations, in the hope of obtaining some fixed law whereon to base a knowledge of the peculiar influence of the several circumstances on which the varia tions depend.
The chemical analysis of this complex fluid was undertaken by Berzelius, who, with his accustomed accuracy, produced a result in which the various improvements and advances in chemistry have rendered it necessary to make but little change.
The number of constituents of healthy urine has been but little increased by discovery since Berzelius wrote, one or two only having to be added to his list.
It will be our object to enumerate these constituents, and describe such as may require especial notice, before proceeding to consider the quantitative analysis of the urine.
The following, then, may be regarded as a list of the constituents of healthy urine :— Other acids, peculiar to urine, have been described by authors, but their qualities are not sufficiently determined to admit of their being yet classified as constituents.
Urea. — This constituent of the urine has been supposed by some to form during the evaporations necessary for its extraction. This, however, is not the case, as I have been able to obtain it by agitating the officinal rectified ether with urine in the natural state, and then allowing the ethereal solution, which separates above the urine, to evaporate spontaneously. The urea so obtained is free from lactic acid, showing that the view of MM. Cass and Henry, who consider urea to exist in urine in the form of lactate, is in all probability erroneous.
Urea possesses the following ultimate con stitution:— C2, N2, H4, 02.
Its chemical properties are as When heated on platinum foil it fuses, and on the heat being urged, it yields fumes of carbonate of ammonia. It is very soluble in both cold and warm water.
A concentrated solution of urea will bear a heat of 212° Fehr. without decomposition, but it quickly decomposes at that temperature when in dilute solution.
Alcohol of specific gravity 0.816 dissolves one-fifth of its weight of urea at 60° Fahr. ; boiling alcohol dissolves nearly its own weight.
Urea is slightly soluble in ether.
The caustic alkalies boiled with urea de compose it into carbonate of ammonia.
The nitric and oxalic acids combine with urea, forming more or less insoluble salts, and on this fact the processes for the extraction of urea, from its combinations, chiefly de pend.