Tube casts are especially indicative of nephritis and exudation into the uriniferous tubes. They are much firmer than the mucous cylinders and have smoother and more even margins. If relatively thick and straight they probably come from the straight tubes; if sinuous or twisted, from the convoluted tubes. With a similar basis substance they often enclose different solid bodies and have been named accordingly:—epithelial casts when containing cylindroid, or polyhedral cells may be unhesitatingly referred to the uriniferous tubules:—granular casts in which the homogeneous cast is impregnated with granular cells and free granules of proteid, fatty, or mineral matter, point directly to inflammation affecting the uriniferous tubules and their epithelial lining:—blood casts enclosing red blood globules imply hemorrhage, or congestion or inflammation of the tubules, with blood extravasation or diapedesis:—casts containing leucocytes and pus cells bespeak suppurative inflammation of the tubules:—calcareous casts entangle numerous crystals and granules, mainly of lime carbonate, and effervesce with acetic acid:—hyaline casts are homogeneous, clear, so transparent that it is sometimes necessary to stain them with iodine or aniline to make them distinct; they are found in nephritis and especially in the chronic forms:—colloid casts or waxy casts, or amyloid casts may designate a class of firmer cylinders, clear, homogeneous and refractive, and often bearing fatty or blood globules, crystals or fungi. They may have a yellow color, or they may give the amyloid mahogany reaction with the iodo-potassic iodide solution (even in the absence of amyloid degeneration of the kidney; Jaksch).
Progress. Acute nephritis may advance for three days or more and then terminate in resolution, or go on to complete anuria with coma, to suppuration, gangrene or chronic nephritis.
Resolution is marked by general improvement of pulse, breathing and expression, clearing of the urine, and return of appetite. The urine may remain albuminous for eight days longer.
Complete suppression of urine has persisted five days in cattle (Funk), and seven days in horses (Friedberger), accompanied by intense fever, dullness, stupor and coma ending in death from uræmia.
Purulent urine is white, milky, albuminous, granular, with epithelial cells and casts and pus cells, showing their double nuclei with acetic acid. There are usually rigor, hyperthermia (106° F.), thirst, intermittent colics, diarrhœa, perspiration, uncertain walk, and stocked legs. Convulsions have been noticed in the horse (Didie), cow (Pflug) and bitch (Trasbot). The horse may turn in a circle (Friedberger) or have amaurosis (Didie). Death usually occurs in two weeks.
Gangrene is likely to prove fatal. Berger has seen death occur in three days in the horse, and Trasbot in four days in a cow, after a large cantharides blister.
Pathological Anatomy. The kidney is enlarged, soft, friable, dark red, yellow with red spots, or having areas of hemorrhage. When fatty it is marbled, pale yellow or white and red. The capsule is easily detached. On section it is bloody, oozing or even dropping blood, or a pale creamy fluid. The pelvis contains urine, thick, gelatinoid, bloody or purulent. The latter condition must not be confounded with the thick pus-like mucus which normally occupies the renal pelvis in the horse.
The lesions of the secreting portions of the kidney will vary with the concentration of the inflammation in one or other of the separate tissues.
In glomerulitis from toxic irritants, the capsules enclose an albuminous liquid exudate, the capillaries are overdistended, their walls thickened and cloudy, and thrombi with an excess of red globules and leucocytes block them at intervals. This capillary obstruction extends to the plexus surrounding the convoluted tubules.
In tubular nephritis there is congestion of the plexus covering the convoluted tubes, and the epithelium shows cloudy swelling, with fatty granules and hyalin droplets in the desquamating cells.