A low specific gravity, 1015 or thereby, should lead to testing for albumin, not because the presence of albumin lowers the specific gravity, but because in albuminuria there is frequently a diminished quantity of the usual solids of the urine. A high specific gravity, 1030, 1035, &c., almost surely indicates diabetes. The acidity or alkalinity of the urine is de termined by the use of blue litmus paper, which remains blue if dipped into an alkaline fluid, but is changed to red if the fluid be acid. As already stated, healthy urine is feebly acid when passed. After a little it becomes more acid, and then, with decomposition, it becomes alka line. Urine may be affected in this direction by food and drugs, a diet rich in animal food kendering it highly acid, and one rich in vege table food or alkaline drugs (soda, potash, &c.) tending to make it alkaline. If there is no reason in the food for one condition or the other, further examination is necessary, lest the high degree of acidity indicate excess of uric acid in the system, as in gout or in the condition tending to the formation of uric acid stone, or lest, on the other hand, some affection of the bladder be causing premature decom position of the urine and its consequent alka linity, or lest some other serious condition of body be present.
The detection of albumin in the urine is of great importance. A small quantity of urine is heated to boiling in a test-tube over a gas or spirit-lamp flame, a few drops of acetic acid being added. If albumin be present in any quantity a white flaky precipitate appears, the thickened albumin. Anyone can imitate this test by mixing a small quantity of white of egg with water, placing it in a test-tube and boiling. In extreme cases the urine may become almost solid. A simple way of performing the test is to take some urine in a metal spoon, add a few drops of vinegar, and heat to boiling. If albu min be present in very small quantity this test is not delicate enough. A more satisfactory one is afforded by pouring the urine into a test tube to the depth of from 1 to 2 inches, inclin ing the test-tube to one side, and pouring down the side gently, and drop by drop, strong nitric acid to the extent of half the quantity of urine. Then gently raise the test-tube to the upright position, taking care not to shake the fluid. The nitric acid and urine will be found to form two layers distinct from one another, the heavy nitric acid at the bottom of the tube and the urine above it. If albumin be present a white cloud appears at the junction of the two fluids. The success of the test largely depends on the two fluids being kept from mixing.
To detect bile take a small quantity of urine in a test-tube, drop in a small morsel of lump sugar, incline the test-tube, and slowly pour down the side a quantity of strong sulphuric acid (oil of vitriol) equal to that of urine. The
acid forms a colourless layer at the bottom, urine is above it, and the piece of sugar is be tween the two. Raise the test-tube and watch the junction between the two layers, the fluids being kept from mixing by shaking being pre vented. The appearance of a deep-purple colour indicates the presence of bile. A dark-brown colour of burnt sugar, caused by the action of the acid on the sugar, must not be mistaken for the purple. Bile is present in the urine in jaundice and diseases of the liver, to which refer (pp. 272 to 274). Another method con sists in pouring some urine on a white porce lain plate and pouring beside it some drops of fuming nitric acid (nitric acid containing nitrous acid). At the junction of the fluids there ap pears a play of colours, beginning with green and going on to blue, violet, red, and ending in yellow. Both these tests give satisfactory results only in experienced hands.
To detect sugar in urine there are various tests. Fill a test-tube to one-third with urine, add an equal quantity of liquor potasste, and boil the top of the mixture by causing the flame of a spirit-lamp to play on the side of the tube. The appearance of a sherry-brown colour, deepening on continued boiling, indicates the presence of sugar. Another teat consists in adding a drop or two of solution of sulphate of copper to urine in a test - tube, then enough liquor potassue to give a clear dark-blue solution, then boiling the surface of the mixture. If sugar be present a red or orange coloured pre cipitate appears. The presence of sugar indi cates diabetes.
By examination with the microscope the presence of blood (see Hmmaturia, p. 409), matter, crystals of uric acid or oxalate of lime (see p. 403), cells from the kidneys or urinary passages, casts of the tubules of the kidney, produced by material capable of clotting being poured into the tubes as a result of inflamma tion (see Baleares DISEASE), and other unusual constituents may be detected. The urine is allowed to stand for some time in a conical glass. A glass tube drawn to a fine point is passed down to the bottom, and a few drops of the fluid are withdrawn. A drop is placed on the centre of a glass slide used for microscopical purposes, and covered with a cover-glass. The slide is placed on the stage of a microscope and examined with a lens magnifying by 300 dia meters. The forms of these various bodies are exhibited in Fig. 163.
Albuminurla is the condition in which albumin is found to exist in the urine. It is a symptom of disorder of the kidneys. (See