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.
[Illustration]
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 (H_{2}C_{2}O_{4}.2H_{2}O) in
each cubic centimeter.