PRELIMINARY OPERATIONS.
It is the practice of some physicians to direct the patient to preserve all the urine passed in twenty-four hours, and to forward this in one bottle for analysis. Others, again, merely send a small sample of "morning" and "evening" urine in separate phials, desiring only a comparative report. In the former case the volume should be accurately measured, and the quantity noted either in fluid ounces or cubic centimeters before commencing the analysis. This need not be done if small samples only are received. The color should be noted. It varies greatly, through every shade of yellow and amber to dark brown, with a tinge of green or red, if the coloring matter of bile or blood is present. Also note relative transparency or cloudiness, specific gravity, and reaction, as all these observations are useful in diagnosis. Odor is not quite so important. The specific gravity should be taken at about 60° F. in an ordinary specific gravity bottle, or more conveniently by means of a good urinometer. In the latter case it is very important to have an instrument of known accuracy, many of those in the market being valueless. Urinometers of glass, though fragile, are decidedly more cleanly and less liable to get out of order than the gilded brass instruments carried in the pocket by many physicians. Mr. J.J. Hicks, of 8 Hatton Garden, E.C., manufactures a very creditable "patent urinometer" at an extremely low cost. Healthy urine has a density of from 1.015 to 1.025; but variations from this range are common.
A fair quantity of the urine, after shaking, should be placed in a tall conical glass vessel, to allow easy collection of the precipitate for subsequent, microscopical examination. If an abundant amorphous deposit of a fawn or pink—from uroerythrin—color slowly settles and is readily diffused, urates in excess can be anticipated. Their presence is proved by the readiness with which they dissolve on warming with the supernatant urine to about the temperature of the blood. No difficulty is experienced if small quantities of albumen are present, as that body is not coagulated until the temperature rises much higher. A sandy precipitate of free uric acid will not dissolve on warming the urine, and its identity can further be determined by means of the microscope, or by applying a well-known color-reaction. A grain or so is oxidized into reddish alloxan and alloxantin by carefuly evaporating with a few drops of strong nitric acid on a piece of porcelain. A little ammonia is then added, when the fine purple murexide stain will be produced.
It is always advisable to mention the reaction to test papers of all samples received. Urine is normally acid, but there are certain diseases which render fluid neutral or alkaline. The urea of acid urine on standing is changed by a putrefactive ferment into ammonic carbonate, but this decomposition in a state of health should not take place for at least twenty-four hours. Alkalies, or organic salts of alkaline metals, when taken as medicine render the urine alkaline, and the indication is then not of much moment; but if none of these causes exist, the condition is of serious diagnostic import. Where it is desired to determine the degree of acidity of the urine voided, say, by a gouty patient, a dilute volumetric solution of caustic soda should be employed, using a few drops of an alcoholic solution of phenolphthalein as an indicator, and reporting in terms of oxalic acid. The soda solution may conveniently contain the equivalent of one milligramme of recrystallized oxalic acid (H2C2O4.2H2O) in each cubic centimeter.