Causes. It may be determined by local irritation caused by the passage of the bacteria and toxins of infectious diseases such as influenza or contagious pneumonia. In the same way irritant diuretics, medicinal, alimentary and toxic, operate. Diuretic balls and condition powders given recklessly by stablemen and grooms, saltpeter, resin, oleo resins, turpentine, rue, savin, colchicum, squill, anemone nemorosa, adonis, cynanchum vincetoxicum and other species of ascelepias, hellebore, mercurialis annua and bryony are examples. The young shoots of the coniferous plants, fir, balsam fir, pine, white and yellow, and hemlock, are at times injurious.
In the same way, damp moldy oats or fodder produce renal congestion and excessive polyuria, also corrupt, stagnant water and that of marshes which often contains complex toxic products of fermentation. Water of ponds in which cantharides or potato beetles have been drowned, is dangerous. The cantharides, euphorbium or oil of turpentine applied too extensively to the skin as a counter-irritant, is another factor.
Even the rich aqueous grasses of spring succeeding to the dry winter diet, stimulate the kidneys, determining an active congestion with polyuria and in bad cases hæmaturia. In many such cases there are superadded the acrid diuretic plants already referred to. In Denmark where onions are grown on a large scale, the tops fed to animals have produced renal congestion.
There appears to be an extra susceptibility in spring when the winter coat is being shed, and at this time especially, but also independently of this and at other seasons, exposure to cold and the occurrence of chills tend to induce an attack. Exposure to cold storms of rain or sleet when perspiring or fatigued, standing tied out of doors in zero weather without a blanket, wading or swimming deep rivers in cold weather and while fatigued, standing wet and unblanketed in a cold stable when returned from work, exposure to draughts between open windows or doors, the continuous falling of cold rain, from a leaking roof, on the loins, the cold of a damp stable newly finished in brick or stone, the cold and damp of an undrained floor in a wet retentive soil, all have a tendency to drive the blood from the surface, to increase the tension of the blood in the heart and internal organs, to stimulate the kidneys to extraordinary secretory activity, and at the same time to temporarily debilitate the whole system and lessen the power of resistance and recuperation. The factor is especially potent when it involves the nervous interdependent sympathy between the chilled loins or abdomen and the kidneys. Sprains and other injuries of the loins have long been charged with producing renal congestion and inflammation, and even Trasbot, who doubts the reality of this, acknowledges that the already diseased kidneys are seriously injured in this way. Cadeac and Schmid record cases of actual rupture of the horses’ kidney from violent movement, and other cases of congestion and bloody urine have been traced to kicks on the loins, falls, sprains and the carrying of unduly heavy loads. The overexertion which produces albuminuria, casts and sanguineous transfusion in athletes has a similar effect on the overdriven race horse, trotter or draught horse.
Lesions. The congested kidney is enlarged, sometimes to two or three times its natural size, softened, and red, especially in the cortical portion which may be so dark as to appear cyanotic. The capsule is also the seat of ramified redness, and is very loosely adherent to the cortex. Beneath it may be considerable yellowish exudate especially abundant in the vicinity of the hilus. On section the cut surface is very bloody, the cortex literally dropping blood, though brownish spots may appear at intervals representing areas of necrosis, which under pressure break down into a pulpy debris. Microscopically the glomeruli appear hæmorrhagic, the capillary vessels being gorged to excess, while blood globules and even minute blood clots are found in the intervascular spaces. The epithelium covering the glomeruli and lining the convoluted tubes show granular or fatty changes, and granular matter is found outside the vessels.
The congestion is less in the medullary portion and even in the convoluted tubes and the tubes of Henle, though these may be the seat both of hyperæmia and exudation.
In case of very violent congestion, extensive sanguineous extravasation may occur, leading even to rupture of the capsule and the escape of blood into the perirenal adipose tissue or into the abdominal cavity. Cases of this kind in the soliped are recorded by Caroni, Cadeac, Moussu, Kitt, Zundel, Mollereau and Porcher. Averons describes in the Revue Veterinaire (1897) a case in which both kidneys were surrounded by an immense black clot, and weighed no less than 36 lbs. Leblanc records a similar case affecting the one kidney. The mass measured about 10 inches by 8.
Symptoms. These are liable to appear suddenly, often while the patient is at work, and are manifested by weakness in the loins, slow gait or sudden stopping, the hind limbs are held in abduction, and advanced with apparent stiffness and pain. There is much excitement and anxiety, the face is pinched and strained, the respiration accelerated, the pulse hard, tense and rapid, and the eyes or nose may be turned toward the flank or loins. There may be colicy pains, with uneasy movements of the tail and hind limbs, pawing, and even lying down and rolling. The visible mucosæ are strongly injected and in bad cases the skin may be drenched with sweat. There is at first little or no hyperthermia.
At first there may be no micturition but in an hour or more, urine may be discharged in excess, sometimes as much as 25 quarts, and of a low specific gravity (1001 to 1005). If there has been no blood extravasation it is usually clear and limpid but with extravasation it may be of all shades of pink or red to black. In the latter case the suffering is liable to be acute (Cadeac), and contrary to the condition in hæmoglobinuria, the urine contains blood globules and even tubular coagula representing the uriniferous tubes and entangling the blood cells. This is complicated by albuminuria.
Course. Duration. The congestion is short lived. It speedily undergoes resolution with the passage of normal, clear urine, and the recovery of appetite and spirit, or it becomes rapidly aggravated, with continuous suffering and colic, complete loss of appetite, dullness, constant decubitus, weakness, debility, small or imperceptible pulse, palpitations, darker color and perhaps complete suppression of urine, and stupor or other nervous disorder. Death may occur on the fourth to the sixth day. It may be delayed by a partial recovery followed by a relapse.