observe the formation of bubbles from the liberated ammonia. The urate of ammonia gives like the others the murexide test (p. 57).

3. Uric Acid.

The appearance of uric acid in the urine is in part dependent upon the same circumstances as the urates. Normally we find crystals of uric acid at the end of the so-called acid fermentation, also in concentrated urine, especially on summer days, when the higher temperature prevents the deposition of the urates. Finally, a pathological excess is found in those cases where the water and the alkalies do not suffice to retain it in solution.

The primary form of uric acid crystals is that of rhombic plates with blunt rounded corners. This shape is known as the whetstone crystal. The crystals may be small and singly developed. Sometimes rows of these crystals are deposited on accidental impurities, as threads or hairs, and thus form long cylinders. In other cases the single crystals are developed and joined to foreign matters, where they are arranged upon the edges (fan-shaped) or upon the faces (as tiles). Besides the whetstone crystals, we often find tub-shaped or long pointed crystals joined together in a rosette. (Pl. II., B.)

The rough and pointed forms of uric acid have a great practical significance, inasmuch as they are almost always an accompaniment of renal calculi.*

These forms occur only in strongly acid urine. If

* Ultzmann, "Ueber Harnsteinbildung," in "Wiener Klinik," 1875, 5. Heft.

the acid urine is neutralized by the internal administration of fixed alkalies, the forms of the crystals are changed, the pointed forms becoming the normal whetstone-shaped crystals.

The rough and pointed forms of the crystals occur in the urine sediment of pyelitis calculosa, and are fre quently accompanied by albuminuria (hyperæmia of the kidney) and hæmaturia. We also find these forms present without pyelitis or albuminuria. When this is the case, micturition is sometimes painful. In every case the uric acid is colored light yellow, brown-red, or dark brown by the accompanying coloring matters.

The crystals are generally formed so large that they appear on the bottom of the vessel as a glistening brickred sand, which may often be seen by the unaided eye. This sediment dissolves on heating with caustic alkali; partly because some urates are formed, while the remainder of the acid is deoxidized. The sediment gives finally a beautiful murexide reaction.

4. Calcium Oxalate.

Oxalic acid has a strong affinity for calcium. Since calcium salts are present in the urine, the oxalic acid. which is excreted by the kidney or forms in the urine is observed in combination as calcium oxalate. These crystals result, as already mentioned, from the acid fermentation together with uric acid. The shape of the calcium oxalate is very characteristic. The crystals are generally quadrilateral octahedrons which have a strong refractive power. Sometimes they appear as small but

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distinctly angular dots, and sometimes as rectangular plates whose angles are joined by diagonal lines, causing the envelope appearance. Some appear oblique. Besides these principal forms, we sometimes observe dumbbell crystals. (Pl. III., A.) As these crystals have a low specific gravity, they appear only after a long time in the sediment-from twelve to twenty-four hours; after this time has elapsed we must carefully decant and look for the small four-cornered dots.

The characteristic form of the crystals admits of no confusion. The only crystals with which they may be confounded are the triple phosphates. In the first place, however, the calcium-oxalate crystals are never as large. Secondly, calcium oxalate occurs in acid urine, triple phosphates appear in neutral or alkaline. Finally, acetic acid dissolves the triple phosphates, but has no action on the calcium oxalate.

5. Cystine.

Cystine forms regular hexagonal tables of varying size. These occur singly, or we find a large plate at the bottom, and smaller and smaller plates as the series ascends; we also observe a shingle-like series. Sometimes a large crystal breaks, showing the hexagonal cleavage to be still preserved. Small, imperfectly devel oped crystals form irregular lumps. Often the corners of the plates are rounded as if melted off. The crystals are always colorless. (Pl. VI., A.) These crystals can only be confounded with a pure, colorless, rarely occurring form of uric acid. This similarity is observed when

the cystine is precipitated by acetic acid; for, when uric acid is precipitated in the same manner, the forms are similar six-sided plates, but generally not as regular.

In order to ascertain if our crystals under the microscope are cystine, we carefully allow a drop of ammonia to flow under the cover-glass. Instantly the crystals of cystine vanish, while uric acid without the application of heat remains unchanged. As soon as the ammonia has evaporated, the cystine again crystallizes. The reprecipitation is assisted if we add a drop of acetic acid to the ammoniacal solution.

A second test consists in treating the cystine crystals with a drop of hydrochloric or oxalic acid. Cystine dissolves, while the uric acid will remain unchanged.

The form of the crystals and their insolubility in boiling water prevent cystine from being confounded with the urates.

Cystine is soluble in ammonia, but insoluble in carbonate of ammonia. In case the cystine is held in solution in the acid urine at the beginning of the alkaline fermentation, it is precipitated like an earthy phosphate by the carbonate of ammonia generated.

From the earthy phosphates and triple phosphates cystine is easily distinguished by chemical tests, and by the microscope, which shows the earthy phosphates as an amorphous powder, while the triple phosphate presents an entirely different form of crystals.

Acetic acid dissolves the earthy phosphates, but the cystine is unaltered by it. But, if it happens that by addition of acetic acid and heat the greater part of the

sediment dissolves and but a trace remains, this should be brought under the microscope; and, if hexagonal plates appear, they should be treated in the above described manner with ammonia and hydrochloric acid, to distinguish the cystine from uric acid.

If we dissolve cystine in KOH, warm, add water, and then a solution of nitro-prusside of sodium (Nay(CN)5(NO)Fe"), the mixture becomes violet. This reaction also will show albumen or any other compound containing sulphur in the dyad form.

The urine in which we find cystine is mostly pale. When putrefying it develops, besides the ammoniacal odor, that of hydrogen sulphide, which in all probability occurs as a decomposition product of the cystine. The sediment of cystine occurs in connection with cystine stone, and also independently of it. It appears white or dirty yellowish-gray, often with an abundance of triple phosphates and phosphate of calcium; in acid urine, with calcium oxalate.

This sediment seldom occurs with us, but it sometimes happens that many members of a family suffer from cystinuria.

6. Leucine and Tyrosine.

Both of these substances are usually found together in the urine, but mostly in solution. Simple evaporation serves to produce a sediment (p. 124). Tyrosine sometimes appears as a sediment without this treatment.

Under the microscope leucine appears as spheres of various sizes, more or less colored, and having the ap