(unipolar), or they may have spindle-shaped prolongations on both (bipolar caudate cells). (Pl. I., A, 2.) The presence of these cells must not be regarded as an indication of a neoplastic growth, as is stated in the older writings.

3. The flat cells arise either from the bladder or the vagina. They are most irregular, polygonal with rounded corners, and have a sharply defined dark nucleus nearly in the centre. This nucleus bulges out, as may be seen when the cell is standing on its edge, making the cross-section appear like a spindle-cell. (Pl. I., B, 2.)

It is difficult sometimes to distinguish the bladder epithelium from that of the vagina. The bladder epithelium is more delicately formed, and generally appears singly; the epithelium of the vagina is somewhat coarser, has sometimes a warped surface, and is almost always cast off in great cohering shreds; frequently the scales are arranged in layers, an appearance never occurring in bladder epithelium. (Pl. I., B, 4.)

The yellow color of the nuclei of various epithelial cells with icterus is interesting. If we now allow a drop of fuming nitric acid to flow under the glass cover, we observe the nuclei to pass through the color changes of Gmelin's test (green, blue, violet, etc.) (Ultzmann).

3. Pus-corpuscles.

The pus-corpuscles of the urine are quite similar in appearance to those of a suppurating wound. They are

round cells twice as large as blood-corpuscles, with a uniformly granular exterior which surrounds the nuclei. The nuclei may be exhibited more distinctly by the addition of a drop of acetic acid under the cover-glass : the granulation vanishes, the corpuscle swells, and the several centrally placed nuclei become visible. Besides this usual form, there is another of rare occurrence, in which the corpuscles are not round, but have various prolongations which show amoeboid movement. VII., B.)

(Pl.

The pus-corpuscles are changed, especially in ammoniacal urine, under the influence of carbonate of ammonium. They swell up and coalesce, showing under the microscope a homogeneous mass, in which the nuclei alone are distinguishable. Such pus forms a vitreous, slimy mass, which on pouring flows out as a whole, like albumen when poured from one vessel to another.

This must be distinctly emphasized, lest the beginner fall into error in supposing that such a slimy mass is mucus or albumen. The latter does not form a sediment under any conditions, and mucus never forms a like cohering mass. If pus is in the urine, pus-serum and albumen must also be present. We may always obtain the albumen-test, which is not the case with mucus.

is

The amount of pus-corpuscles is various. Often the urine contains so few that they (forming no sediment) escape the unaided eye. In some urines so much pus present that a sediment several fingers high is formed of a yellowish or grayish white color.

A confusion with the urates is possible in acid

urines, and with the phosphates in alkaline. We have already described the tests for the urates. The phosphates disappear on addition of a few drops of acetic acid; pus does not.

Donné's test permits the distinction without the aid of the microscope. Pour the urine from the sediment, and add a little piece of caustic soda or potassa. If the sediment consist of pus, then it will lose its white color, becoming greenish and vitreous, first stringy, then thicker, until finally it forms a cohesive lump. It has in this manner taken on the appearance of pus in a strongly alkaline urine. Since no other body in the urine can give this reaction, it is a perfectly safe method of distinguishing pus. If the amount of pus is scanty, one can not expect to obtain the cohesive lump, but on the contrary the sediment disappears and the fluid becomes vitreous and stringy.

With the sediment are mixed broken-down pus-corpuscles (detritus), and frequently blood-corpuscles, epithelial cells, etc.

4. Blood-Corpuscles.

Blood-corpuscles in the urine may be distinctly recognized when present in but small amount. If the urine is tinged a brownish red, and the suspicion arises that blood-coloring matters or corpuscles are mixed with it, we allow it to stand for some time, in order that the light and sparingly present blood-corpuscles may form a sediment (often but a trace), which is colored a beautiful red.

In acid urine the blood-corpuscles retain their characteristic form for a long time. They exhibit small disks, which show a central shadow corresponding to the depression. If the blood-corpuscles stand on their edges, they appear bi-concave. They are always single (except in profuse hæmorrhages from the bladder, when they form rouleaux), and appear reddish with a slight greenish tinge.

This original form of the blood-corpuscle undergoes many changes, brought about by the nature of the menstruum in which the corpuscles are distributed. If the urine is very dilute, especially if it has begun to be ammoniacal, the corpuscles swell, the depression disappears, and they become spherical, appearing somewhat smaller than before. The central shadow vanishes with the depression, and instead the corpuscle has a peripheral shadow by which it is recognized as a sphere.

By longer exposure to the above influences, the corpuscle becomes more indistinct and appears as a delicate bubble, which then becomes but a mere shadow in the field, finally disappearing.

By treatment with a neutral-salt solution the bloodcorpuscles become smaller and jagged. These jagged forms are observed in the urine, often in connection with the normal. The corpuscles appear to have produced within themselves small crystals whose ends cause the limiting membrane to become distorted. Sometimes the corpuscles are not round but oval, and are of various sizes in the same urine; sometimes cup

shaped.

(Pl. V., A, 2.)

In hæmaturia which accompanies parenchymatous affections of the kidney and bladder, we find almost always spherical corpuscles of different sizes. Quite small, even dust-like blood-corpuscles (microcytes) occur in such cases with normal and greater forms (macrocytes).

No matter how small an amount of blood-corpuscles is present, it is always possible to prove the presence of albumen in connection.

If the blood-corpuscles have been dissolved in an ammoniacal urine, we may test for the coloring matters (hæmo- or methæmo-globine), as described on page 68.

Regarding the origin of blood-corpuscles in the urine, the subject is treated of in Chapter VIII.

5. Cylinders.

The identification of cylinders plays a most important part in the diagnosis of kidney diseases; for by their form they betray their place of origin in the urinary tubules. In the investigation of the urine, the greatest care must be taken that these be not overlooked. By their low specific gravity they remain for a long time suspended in the urine. To this may be added the circumstance that their appearance is generally accompanied with albuminuria, and in the albuminous fluid their precipitation is very slow.

The precautions necessary for the investigation of these forms are as follows: The urine must be permitted to stand for several hours, then carefully decanted,