Normal urine is free from coagulable proteids, though it is admitted
that albumen may sometimes occur in the absence of disease. It is
always highly important, therefore, to determine accurately the
presence or absence of this body. In the relentless malady named after
Richard Bright, the urine always contains albumen, and if accompanied
by the "casts" of the uriniferous tubules your report may amount to a
sentence of certain death. The tests which we now describe are
accurate and easily applied; but reliance should never be placed on
any single reaction--at any rate until the operator has acquired
considerable experience.
Galippe's _picric acid test_ has within the last few years attracted
much attention, chiefly through the commendation it has received from
Dr. George Johnson. A saturated solution is prepared by dissolving 140
grains of recrystallized picric acid (carbazotic acid, or, more
correctly, trinitrophenol) in 1 pint of water with heat, and decanting
the clear solution. Some of the urine is rendered perfectly bright by
filtration--repeated, if necessary--through good filtering paper, and
to this an equal volume of the picric acid solution is added. In the
presence of albumen a more or less distinct haze is produced, which on
heating to the boiling point is rather intensified than otherwise.
Peptones, if present, yield a similar haze, and quinine or other
alkaloid a more or less crystalline precipitate; but in both these
cases the opalescence is completely dissipated by heat. Mucin, an
important constituent of some urines, is not affected by picric acid,
and the test is decidedly one of great value.
The _nitric acid test_. Heller's contact method, which can also be
used with the last-described reagent, is the best mode of applying the
old-fashioned and favorite test with nitric acid. To 5 volumes of a
filtered saturated solution of magnesic sulphate, prepared by
dissolving 10 parts of the salt in 13 parts of distilled water, add 1
volume of strong nitric acid, and label "Sir W. Roberts' nitric acid
reagent." A couple of drachms of bright filtered urine is allowed to
float on an equal quantity of this solution in a test tube; care being
taken that the contact line is sharply defined. In a period of time
varying from a few seconds to a quarter of an hour, according to the
amount of albumen present, a delicate opalescent zone forms at the
point of junction, and if mucin also is present, a more diffused haze
higher up in the urine. Special attention should be given to the
position of the opacity. In some concentrated urines a belt of urates
will appear at the line of demarkation; but these dissolve on warming.
Moreover, owing to the dilution necessary in the mode of applying
Galippe's picric acid test, they are not so readily shown by the
latter. A ½ oz. glass syringe can very conveniently be substituted for
a test tube in making analyses according to Heller's method. Some of
the urine should be drawn up, and then an equal volume of the reagent.
On setting aside, the albumen ring will rapidly develop.
The _boiling test_. This method also is very delicate and valuable. It
depends on the well-known property possessed by many proteids of
coagulating under the influence of heat. The urine should have an acid
reaction to test paper; if alkaline, it must be cautiously neutralized
with dilute acetic acid. In either case a single drop of strong acetic
acid should be added to about three drachms of the bright liquid. If
this precaution is omitted, there is danger of precipitating earthy
phosphates on heating; and should a great excess of acid be employed,
a non-coagulable form of albumen known as syntonin is formed, besides
increasing the likelihood of precipitating mucin. Place the prepared
urine in a narrow test-tube and hold it in a small flame so that the
upper part only of the liquid approaches the boiling point. By this
means very small traces of albumen are easily observed, the
opalescence produced contrasting strongly with the cold and clear
fluid beneath.
The _ferrocyanide test_. Hydroferrocyanic acid yields a precipitate
immediately in the presence of much albumen, and if traces only are
present, in the course of a few minutes. To apply the test, strongly
acidulate with acetic acid, and then add a few drops of recently
prepared potassic ferrocyanide solution. This is one of the most
delicate tests known.
It is often desirable that the percentage of albumen present should be
determined at frequent intervals, in order to note the success or
otherwise of the physician's treatment. These quantitative
determinations, being intended only for comparative purposes, do not
demand any very excessive degree of accuracy, such as would be
difficult to obtain in ordinary practice. The recent method of a
Continental worker. Dr. Esbach, affords indications sufficiently
precise for therapeutical requirements, and is at the same time
extremely easy of application. The filtered acid urine is poured into
the glass tube up to the mark U, and then the special reagent is added
till the level of the liquid stands at R.
[Illustration]
Mix the liquids thoroughly, without shaking, by reversing the tube a
dozen times, close with a cork, and allow it to stand upright for
twenty-four hours. The height at which the coagulum then stands, read
off on the scale, will indicate the number of parts per thousand, or
grammes of albumen in one liter. This divided by ten gives the
percentage. Dr. Esbach's test solution is prepared by dissolving 10
grammes of picric acid and 20 grammes of citric acid in 900 c.c. of
boiling distilled water, and then adding, when cold, sufficient water
to yield 1 liter. The citric acid is only employed for the purpose of
maintaining the acidity of the liquid, and is really not essential.