PLATE VIII.

URATES.

Deposits of urates are usually bulky and tolerably dense, leaving a clear or more or less turbid supernatant fluid. The urate is almost invariably deposited after the Urine has left the bladder.

The colour of these deposits varies greatly. Rarely they are perfectly colourless, but usually have a yellowish or pale brown colour (lateritious and nut-brown sediment), sometimes they are pink, dark brown, or even bright red.

Urates are soluble in warm water and are usually dissolved in the Urine upon the application of warmth. They are readily dissolved by alkalies. By adding excess of acid to the alkaline solution uric acid is precipitated in a crystalline form. By being treated with nitric acid and subsequently with ammonia they give rise to the development of the beautiful purple colour, characteristic of murexide. Tables, § 17, b. 33.

Granular appearance. The deposit of urate usually appears granular, even when subjected to examination with very high powers. Not unfrequently by the pressure of the glass, the mass is made to form lines, as shown in fig. 1, in which case these must not be mistaken for granular casts, which they very closely resemble. Upon careful examination, however, the sharp, well-defined outline, characteristic of the cast is not to be found. Masses like those represented in fig. 2 are not uncommon in deposits of urates, especially after they have been allowed to stand for a considerable time.

The beautiful spherical crystals, delineated in fig. 5, are not uncommon in the Urine of children suffering from acute febrile complaints. I have only met with the curious crystals, delineated in fig. 6, in one case,

PLATE VIII.

URATES,

Fig. 1. Ordinary granular deposit, usually termed urate or lithate of ammonia, but consisting of urate of soda with small quantities of urates of ammonia, lime, and magnesia.

Fig. 2. Urate of soda, forming nearly spherical masses, from various parts of which project very minute acicular crystals of uric acid.

Fig. 3. Urate of ammonia prepared artificially.

Fig. 4. Urate of soda prepared artificially.

Fig. 5, Urate of soda in a globular form, commonly found in the Urine of children, This specimen is mounted in Canada balsam.

Fig. 6. Urate of soda in masses, from which irregular root-like processes project. This is a rare form of urate deposit. The specimen from which the figure is copied was obtained from the Urine of a case of peritonitis.

PLATE IX.

TRIPLE OR AMMONIACO-MAGNESIAN PHOSPHATE.

Triple phosphate always exists in healthy Urine in a state of solution, and may be precipitated by the addition of ammonia (fig. 2). The mere presence of the crystals in a deposit does not, therefore, necessarily indicate an excessive excretion of the salt from the organism, but merely shows that it exists in the Urine in an insoluble, instead of in a soluble condition. In some cases a large amount of phosphate exists in solution in the Urine, which the practitioner could estimate only by a careful chemical analysis.

Triple phosphate is insoluble in alkalies but soluble in weak acids. Urine may, however, exhibit a distinctly acid reaction although it contains an abundant deposit of triple phosphate. After having been dissolved by an acid, triple phosphate can always be reprecipitated by the subsequent addition of excess of ammonia.

This deposit, associated with amorphous granules of phosphate of lime, is very often present in cases in which the mucous membrane of the bladder is more or less diseased, and in cases of paraplegia and other conditions where the contractile power of the bladder is impaired and the Urine permitted to remain for a considerable time in the organ. The mucus acts as a ferment and decomposes the urea. Carbonate of ammonia is formed, which precipitates the phosphates in an insoluble form. When pus is formed, it is converted into a glairy mucuslike mass in which a number of brilliant sparkling crystals of triple phosphate are entangled.

Crystals of triple phosphate, when preserved as permanent objects for the microscope, must be kept in a dilute solution of muriate ammonia, in which the crystals are quite insoluble. In this solution they will preserve their brilliancy for a length of time.