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.