C. Specific Gravity

This is either above or below the normal standard. It is excessive in diabetes mellitus, and very low in diabetes insipidus. In the chronic form of Bright's disease it is diminished, as the proportion of urea and of the urinary salts is diminished, at the same time that the albumen increases; in the acute form it is not unfre-quently increased.

3. As regards the chemical composition of the urine, we find that the normal constituents exist in irregular proportions, or that there are new and unusual substances.

a. The watery portion of the urine is in excess in numerous affections of the nervous system, in hysteria, in diabetes insipidus, and according to Rayer and older observers, in advanced age; its quantity is too small in proportion to the solid constituents in the saturated urine of acute diseases, especially at the period at which critical discharges occur.

b. The urea does not, as was formerly believed, bear a direct relation to the coloring matter of the urine, a fact that has been distinctly proved by Prout in some cases of diabetes insipidus. It is more frequently morbidly diminished, as in diabetes mellitus, in Bright's disease, and numerous other diseases that have not as yet been clearly diagnosed, and in which, as the urea disappears, albumen is substituted.

Original deficiency of urea is to be carefully distinguished from that deficiency which results from its decomposition in consequence of stagnation in the urinary passages, from the influence of mucus, purulent secretion, and pus.

C. Uric Acid

Uric Acid, either free or combined with a base, and especially in the shape of urate of ammonia, is deposited in the form of small crystals, or of a yellow or lateritious powder. It is increased in quantity in rheumatism, gout, and inflammatory affections; in hysterical urine, in the urine voided during the cold stage of intermittent fever, and in numerous other diseases, it is diminished in quantity. If free acid is present in the urine it may be precipitated in the shape of gravel, though not itself in excess.

D. The Phosphates

The Phosphates (phosphate of lime, phosphate of magnesia, and triple phosphate of ammonia and magnesia) are often present in excess. Phosphate of lime is deposited in the absence of a free acid, and phosphate of ammonia and magnesia, as a basic salt; these form the phosphatic sediments. As the latter salt is formed in consequence of the development of ammonia, it occurs principally in urine containing much mucus, pus, seminal fluid, and other animal substances that are easily decomposed. The lithic acid is, at the same time, proportionally diminished, and the urine is neutral or alkaline.

e. The alkaline state of the urine is of extreme importance; in many cases that have not as yet met with a sufficient explanation, it appears to be the result of a morbid secretion, or it depends upon decomposition of the urine, and presents various degrees. The urine in this condition is commonly pale and turbid. It is particularly alkaline in chronic inflammation of the kidney, and in numerous diseases of the urinary passages; it is so sometimes in a slight degree, and temporarily, in Bright's disease. The alkaline state of the urine in diseases of the spinal cord, in paraplegia, has attracted some attention, and has given rise to the question, whether this alkalescence is the result of a simple derangement of the act of secretion, i. e. whether the urine is secreted as an alkaline fluid; or whether an acid urine becomes alkaline in consequence of decomposition, by means of the products of coexistent cystitis or nephritis. The question has not received a satisfactory reply. Post-mortem examinations have generally demonstrated the existence of the latter series of causes of alkaline urine; the examinations of the urine in living subjects have been either neglected in the class of cases that come under this head, or they have but little value, on account of the insufficient diagnosis of existing inflammation of the urinary passages and the kidneys. The only proofs in evidence of alkaline urine being secreted by the kidneys, are afforded by the vivisections of Krimer and others, in which, after the division of the spinal cord, urine of the appearance of pure water was secreted; and by the clear neutral or alkaline urine passed in hysterical or epileptic attacks. Rayer has found the urine acid in cases of recent paraplegia, unaccompanied by retention of urine.

The following substances are rarely found as constituents of the urine: a. Purpuric acid, a modification of lithic acid, produced by the presence of nitric acid, and purpurates (purpurates of ammonia and soda), which are said to give a red color to the urinary sediments (Prout).

3. Hippuric Acid (Liebig)

Hippuric Acid (Liebig), which has been found in children in the shape of hippurate of soda, and in diabetes.

y. Oxalic acid is, according to Prout, the result of a decomposition of lithic acid, and occurs as oxalate of lime, in the form of a greenish or blackish sediment, or of gravel or calculous concretion.

d. Benzoic, butyric, and cyanic acid, cyanurin and melanurin in blue and black urine, xanthic oxide (Marcet), and cystin (Wollaston).

e. Sugar, in varying proportions, in diabetes mellitus. C. Cholesterin.