CONSTITUENTS NORMAL AND ADVENTITIOUS - THE URINE.
most important of the solid constituents of the urine is urea, of which a healthy adult excretes every day about 500 grains. While the specific gravity of the urine gives a general idea of the rela tive quantity of urea, yet there are sources of error. It is best to get the whole daily excretion of urea for several days by the hypobromite method. The principal importance of this is in determining the prognosis of cases of chronic nephritis. When the daily excretion of urea is much below the normal the prognosis is bad, although the patients may seem to be doing well.
Urates, Oxalates, and Phosphates. —The presence of an excess of uric acid, of the urates, of oxalate of lime, and of the phosphates is of importance, not because it indicates disease or disturbance of functions of the kidneys, but because it shows disordered digestion and an abnormal condition of the blood. There are many cases of kidney disease in which the treatment of these disturbances is of the • greatest importance.
Blood. —Hmaturia is an evidence of bleeding from some part of the genito-urivary tract. So far as the kidneys are concerned the blood comes from their pelves, or from the kidneys themselves. Bleed ing from the pelvis occurs with pyelitis, with calculi in the pelvis, and with new growths of the pelvis. Bleeding from the kidney itself is found with acute nephritis, with exacerbations of chronic nephritis, with tubercular nephritis, with the hemorrhagic forms of the infec tious diseases, and with malignant growths.
Hamiog/obiatbria. —There are morbid conditions in which a con siderable number of red blood cells are suddenly killed and the coloring-matter set free in the blood. This is followed by a dis charge of this coloriug-matter, with a considerable transudation of blood serum from the kidneys, in the urine. We find then a good deal of albumin and of red coloring-matter in the urine, but no red blood cells.
Casts.—There has been some difference of opinion as to the mode of formation of the little cylindrical bodies which are found in the urine and in the kidney tubules. The question has been whether they are all formed of substances coagulated from the blood plasma, or whether some are formed of substances derived from the renal epithelium.
Certainly most of them are formed from the blood plasma. They are composed of a transparent, homogeneous matter with which may be mixed renal epithelium, white and red blood-cells, and the granular matter, fat, and nuclei derived from degenerated epithelium. The presence of casts in the urine means, therefore, that there has been an exudation of blood serum into the kidney tubules and more or less de generation of the renal epithelium. The number of casts in the urine is usually an indication of the number formed in the kidneys, but not always; we may find but few casts in the urine during life and yet after death the kidneys are seen to contain a large number. Albumin and casts are usually present in proportionate quantities : if there is much albumin there are generally many casts, but albumin may be present in large quantities with very few casts. The centrifugal ma chines which are now in use are of great assistance in looking for casts.
Any one who wishes to understand casts and their mode of forma tion must look at them in kidney sections, as well as in the urine. It seems hardly necessary to warn against confounding cylindrical strings of mucus formed in the bladder, often having crystals im bedded in them, with casts formed in the kidney tubules, but the mistake is sometimes made.
Hyaline casts in small numbers, like albumin in quantities, are occasionally present without disease of the kidneys.
Acute congestion of the kidneys often gives hyaline casts, some times granular and nucleated casts.
Chronic congestion gives a few hyaline casts.
Acute degeneration gives casts according to its severity—hyaline casts only, or granular and nucleated casts, or epithelial and blood casts.
Chronic degeneration gives only a few hyaline casts, or none at all.
Acute exudative and acute diffuse nephritis give many casts of every kind.
Chronic nephritis with exudation gives many casts of all kinds, their number being much increased when there is an exacerbation of the nephritis.
Chronic nephritis without exudation gives a.few hyaline casts or none at all.
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