or mineral waters containing them, appear long quadrilateral tables of basic magnesium phosphate, Mg,(PO4)2 +17H2O, two opposite angles of which have been truncated. If we allow a drop of a solution of commercial ammonium carbonate, in five parts of water, to flow over these crystals beneath the cover-glass, they become opaque, and appear like rough leather gnawed on the edges.

Calcium phosphate does not become opaque, and is more slowly affected by such treatment. Triple phosphates are not altered.

This sediment is very rare, and can only develop in urine which is strongly concentrated and is originally neutral or alkaline. If the urine becomes alkaline from the urea decomposition, there is naturally no magnesium phosphate, but we have ammonio-magnesium phosphate.

10. Triple Phosphates.

These appear as large, clear, refracting crystals, with distinct smooth surfaces and sharp edges. Among the many combinations of the rhombic and very frequently partially amorphous shapes, the coffin-lid crystals are the most common. (Pl. III., B.) They might be confused only with sodium chloride or calcium oxalate; but sodium chloride only appears as crystals in evaporated urine. From calcium oxalate they may be distin guished by adding a drop of acetic acid; if the sediment dissolves, it is triple phosphates; if it remains unchanged, it is calcium oxalate. The conditions under

which these occur have been spoken of under earthy phosphates.

11. Calcium Carbonate.

The urine of most herbivora is already cloudy when evacuated. The turbidity arises from the mass of the excreted calcium carbonate. Only exceptionally is such a condition found in man, though it sometimes occurs a short time after the urine is evacuated. The causes of this are somewhat obscure.

This sediment does not come down by itself, but in connection with the earthy phosphates, forming a more or less fine grained powder, and sometimes dumb-bell crystals. (Pl. VI., B.) We can recognize this precipitate by its solubility with effervescence on addition of mineral acids. This may be observed under the microscope. If, by placing a thread or a hair under the coverglass, we allow a drop of HCl to reach the sediment, then we see gas bubbles of carbonic acid developed. This reaction is never observed with pure earthy phosphates. The sediment must be previously washed carefully with water on a filter to remove any ammonium carbonate (which with acids would also cause effervescence).

Organized Sediment.

1. Mucus.

Considerable mucus may be contained in the urine and not be noticed, because of its transparency, and the slight difference of its refractive power from that of the

urine. Only after long standing, when the urates begin to come down, when the urine contains more epithelium than usual, or when there is a rapid and considerable development of bacteria, does the mucus form the beforementioned nubecula.

If these conditions are not fulfilled, we color the urine.

If there is no albumen in the urine, we precipitate the mucus with alcohol to which some tincture of iodine

has been added, as a stringy mass. Or the mucus may be precipitated by acetic acid to which has been added a little of a solution of iodine dissolved in potassium iodide. The acetic acid causes a turbidity of the mucine in solution, which is not affected by an excess of this acid, but which vanishes upon addition of a couple of drops of HCl.

If the turbidity of the urine disappears by application of heat, we know it was not due to mucus, but to the urates. Mucus has no characteristic form under the microscope; we find only crystals of oxalate of lime and uric acid, as well as mucus-corpuscles (young cells) or bladder epithelium which have been held in suspension by the mucus.

Mucus coagulated by acetic acid, however, shows under the microscope a granulated mass, for the most part striated bundles, sometimes simulating casts and cylinders.

In women we generally find a much greater nubecula, because the urine is usually mixed with a great quantity of vaginal mucus, especially with fluor albus.

Since mucine only swells in water and undergoes no real solution, we may separate it from the urine by filtration. The mucus remains on the filter, and appears there when dry as a glistening varnish. Urines containing much mucus filter badly, for the reason that the pores of the paper are stopped.

2. Epithelium.

We have already mentioned the young cells as mucus-corpuscles. Other cells appear in the urine which serve as an epithelial covering for the mucous membrane of the urinary apparatus, or as the proper glandular tissue of the kidneys.

Manifold as the forms of the epithelial cells appear, if we examine the various parts of the urinary apparatus, we do not find all these forms represented in the urine. The urine, as a fluid containing various salts in solution, works a change upon the epithelial cells. Three forms may with certainty be distinguished: 1. Round cells; 2. Conical and caudate cells; 3. Flat cells.

1. The round cells arise from the tubules of the kidney, and from the deeper layers of the mucous membrane of the kidney-pelvis. In their original form they are more or less oppositely flattened, corresponding to their position beside one another. (Pl. I., A, 1.) Under the influence of the urine they swell and become globular. They have a clearly defined nucleus, and are by this easily distinguished from the pus-corpuscles which also appear in the sediment. The pus-cells are

uniformly granulated, and show their nuclei with distinctness upon addition of acetic acid. The epithelial cells contain but one nucleus, the pus-cells two, three, and sometimes more; besides, the epithelial cells are larger.

In acid urine the epithelial cells are preserved a long time, but if the urine is neutral or alkaline they appear greatly swollen, nearly hyaline, the granular protoplasm entirely surrounding the nucleus; after a time they become wholly dissolved. The epithelium of the male urethra is very similar to the kidney epithelium, so that it is difficult to distinguish one from the other under the microscope. (Pl. I., B, 1.) The distinction is usually based upon the chemical constitu tion of the urine. If the urine contains albumen, the round cells are due to a desquamation from the urinary tubules. If albumen is not present, the round cells are probably from the urethra.

The epithelium of the prostate, Cowper's, and Littre's glands is similar to that of the urethra, and can not be distinguished from it microscopically. With mucus and pus the epithelium forms the so-called gonorrhoeal threads. (Pl. VI., A, 2.)

2. The conical and caudate cells have their origin in most cases in the pelvis of the kidney. Very delicate cylindrical cells come also from the accessory organs of the male urinary apparatus, though they are of rare occurrence. The cells are generally twice as long as broad, and are smaller at one end than at the other. The caudate cells may have a prolongation on one end