224 URINE blance in different classes of animals, accom- panied by special variations in regard to par- ticular ingredients. In the human subject the urine is a light amber-colored fluid, of a watery consistency, a moderately acid reaction, and an average specific gravity of r024. Its aver- age daily quantity is 35 fluid ounces, or 2J pints ; but this amount varies, within certain limits, according to the quantity of fluid taken with the food and drink, and that lost by per- spiration or otherwise. If the amount of drink be unusually abundant, a part at least of the water so taken will pass off by the kidneys, and the urine will be increased in proportion. On the other hand, should the perspiration from any cause be unusually active, less fluid will be discharged by the kidneys, and the amount of urine will be consequently di- minished. These variations evidently depend simply upon the fluctuation of the watery in- gredients of the urine, while its solid constit- uents are comparatively unchanged in amount. Accordingly, its physical qualities, particularly its color, specific gravity, and acidity, vary un- der these circumstances in inverse ratio to its quantity. When the urine is abundant from excess of water, it is paler than usual, its acid reaction loss marked, and its specific gravity diminished. When it is lessened in amount from deficiency of water, it is more deeply col- ored, of a strongly acid reaction, and of a high specific gravity. Variations of this kind occur from day to day, owing to incidental causes, and are strictly within the limits of health ; since the solid ingredients of the excretion, representing the products of bodily metamor- phosis, are still discharged, in either case, in their duo proportion. Similar fluctuations in the density, color, and acidity of the urine take place naturally at various periods of the day ; that passed in the latter part of the day, during the night, and on first rising in the morning, being usually of a deep color, decidedly acid, and of a high specific gravity, often as much asl'028; while that passed during the fore- noon and middle of the day is comparatively pale, often neutral or but slightly acid, and of a specific gravity sometimes as low as 1-016 or T018. The specific gravity 1'02-i represents the average density of all the urine passed during 24 hours in a state of health. The average constitution of human urine is : i of soda i iof potassa V i of ammonia j Water gg^OO rea - 80-00 Creatme j .05 Creatinine Urate of soda Orate Urate of Biphosphate of soda.. . ' Phosphate of soda Phosphate of potassa.. L . l-'-iS Phosphate of lime Phosphate of magnesia Chloride of sodium ) Chloride of potassium.. ( 7' SO Sulphate of soda i Sulphate of potassa. ... if 6'90 Coloring matter and mucus -30 Total. 1000-00 Of these ingredients urea is the most charac- teristic and important. It is a nitrogenized crystallizable substance, freely soluble in wa- ter, and exists in very minute proportion in the healthy blood of man and mammals gen- erally. It represents one product of the phy- siological waste or retrograde metamorphosis of the- system, though it is not yet certain from what special set of tissues or organs it is derived. It ia increased by muscular exer- tion or by a diet of animal food, and dimin- ished by repose or by a diet consisting of vege- table and non-nitrogenous substances. It is constantly eliminated from the blood by the kidneys, during its circulation through their ves- sels ; and this explains the fact that, although it exists in healthy blood only in the propor- tion of (H6 part per thousand, it is found in the urine in the proportion of 30 parts per thousand. It is, in fact, constantly drained away from the blood and accumulated in the urine, to be thus discharged from the body. The average quantity in which urea is produced and discharged in man during health is 500 grains a day. If, from ligature of the renal arteries or disabling affections of the kidney, the urea is retained and allowed to accumulate in the blood, it becomes poisonous as soon as its quantity has increased to a certain point, and signs of disturbance of the nervous system and of nutrition generally come on, and be- come constantly aggravated until they termi- nate in death. This happens more particularly in both the acute and chronic form of Bright's disease. (See ALBUMINURIA.) Creatine and creatinine are also both nitrogenous crystalli- zable substances, products of disintegration. They are produced in the muscular tissue, from which they are absorbed by the blood, and thence in turn eliminated by the kidneys. The unites of soda, potassa, and ammonia are com- binations of these bases with a nitrogenous acid body of organic origin, namely, uric acid. Uric acid by itself is extremely insoluble in watery fluids, but its saline combinations with the above named alkaline bases are readily soluble in the proportions of water usually existing in the urine. They may however bo decomposed by the addition of a free acid to the urine, or by the development of such an acid in it from the changes of decomposi- tion. The new acid then combines with the alkaline bases, and the insoluble uric acid thus set free is deposited in the crystalline form. It is in this way that "uric acid gravel" is formed in the urine, or that calculi composed of uric acid increase in size. The quantity of urates ordinarily discharged by the urine in health is about 25 grains a day. The acid re- action of the urine is due to the presence of the biphosphate of soda, the solutions of which are acid to test paper. The alkaline phos- phates, that is, the phosphate of soda and the phosphate of potassa, are themselves soluble in water. The earthy phosphates, on the oth- er hand, that is, the phosphate of lime and the
