urinary tract, blood-corpuscles, pus-cells, and casts. Besides these, one may have multicellular structures from the kidneys or bladder, and parts of morbid growths in these organs, and lastly micro-organisms which have been taking part in infective processes

FIG. 46.-Tyrosin crystals (Ogden).

through the urinary tract or have been caught in the urine after it has been passed.

Epithelial Cells.-In every normal urine on careful examination will be found a certain number of cells derived from different portions of the genitourinary tract. These cells differ widely in size and shape, and a certain amount of reliance may be placed on the distinguishing features when a sufficient number of the cells of like form are found. This is especially the case where the pathological evidence is supported by clinical symptoms.

It must be remembered that a positive opinion cannot be formed as to the exact region whence the

cells come, as the changes which occur in the cells in a fluid like the urine are very great indeed. They cannot therefore be expected to appear as

FIG. 47.-Epithelium from various parts of the urinary tract: a, leukocyte (for comparison); b, renal cells; c, superficial pelvic cells; d, deep pelvic cells; e, cells from calices; f, cells from ureter; g, 8, 8, g, g, squamous epithelium from the bladder; h, h, neck-of-bladder cells; i, epithelium from prostatic urethra; k, urethral cells; 7, 1, scaly epithelium; m, m', cells from seminal passages; n, compound granule cells; o, fatty renal cell (Ogden).

they do in their normal position in the organ or tissue itself.

The epithelia from the uriniferous tubules are small and simulate pus-corpuscles closely. They are, as a rule, difficult to distinguish from the latter, but are, on the whole, somewhat larger in size.

The cells from the pelvis of the kidney are large, usually flattened and irregular in shape. They often present irregular ameba-like processes, which are somewhat characteristic.

The ureteral epithelium is always present in small amount in the urine, larger quantities being present in cases of renal colic. These cells are distinguished by their nearly spherical shape. They usually appear in association with cells from the pelvis of the kidney when the affection is renal colic.

The epithelia of the bladder are by far the most frequently occurring form in the urine, and their appearance is often of no pathological significance. They are the largest cells in the urinary tract. The number is enormously increased in cases of cystitis, due to whatever cause, and in this affection are always accompanied by pus-cells. The epithelia from the superficial layer of the bladder are flat, large, and highly irregular in outline. Several epithelia are often clustered together to form masses of cells.

The cuboidal and columnar epithelium from the deeper layers of the wall are found only in pathologic conditions. They are smaller than the cells from the superficial layer and are more regular in outline. The columnar cells will be found to be more or less spindle-shaped. The spindle-cells occur only where the lesion is a deep one in the bladder-wall.

Urethral Epithelium.-These cells are commonly found in inflammations of the lower urinary tract.

They differ widely in their form, owing to the great number of epithelia found from the opening of the bladder to the meatus urinarius. Hence great reliance cannot be placed on a microscopic examination to detect their origin. The occurrence of pus-cells with gonococci, in conjunction with a large number of epithelial cells, will lead one to suspect that the latter have their origin in the urethra, and not at a point higher up.

Vaginal Epithelium.-These cells occur in the urine of females, especially in cases in which an acute or chronic vaginitis exists. They may usually be recognized by their large size, and they contain as a rule both cocci and bacteria. They are frequently found in aggregates of from two to five cells.

Uterine Epithelium.-This form of cell is distinguished by the delicate cilia which are so characteristic. Even when the cilia are broken off by contact with the urine, the remnants of them may be seen as slight projecting points on one end of a somewhat prism-like cell.

Renal Casts.-In all cases of disease of the kidney, and particularly in those which have to do with an affection of the secreting epithelium, there will be found certain organized elements in the urinary sediment which are known as tube-casts. These are in the form of cylinders, which may be either approximately straight or convoluted, and correspond in size to about that of the uriniferous tubules. They may have as their basis either an insoluble albuminous material or amyloid substance, or urates or other salts.

The method of their formation is not known. It has been suggested that they are derived from the coagulation of the albumin and globulin directly from the blood, as a sequence of pathological change in the secreting epithelium itself, or that the cast is a portion of the protoplasm of the epithelium which has been excreted and solidified.

The number of casts present in the urinary sediment will vary widely with the case and the time at which the urine has been taken. In some cases they are so plentiful as to be found without difficulty, while in others it may be only after the most careful examination of several slides and repeated centrifuging that the elements will be made

out.

Care must also be taken not to confuse the casts with substances introduced from without into the urine, and for this reason the urine during sedimentation should be carefully covered, and all sides and cover-slips should be as free from lint and dust as possible.

The commonest forms of casts are: 1. Hyaline casts; 2. Granular casts; 3. Amyloid casts; 4. Epithelial casts; 5. Blood-casts; 6. Fatty casts; 7. Pus-casts; 8. Urate-casts; 9. Bacterial casts.

Hyaline Casts.-The nature of the ground-substance of these casts is unknown. They are the most difficult of all casts to detect in the urine on account of their refractive index being nearly the same as that of the fluid in which they float. It is only, therefore, by careful observation and focussing that they are detected. It is often well in looking