_Lesions._ Thirteen months after the commencement of the attack this horse was destroyed and the cord was found to be profoundly altered by fibroid degeneration of the neuroglia and absorption of the nerve elements (cells and fibres), the lesions affecting different portions of the gray horns, and the columns—superior, lateral and inferior. The affected portion of the cord usually shows in man a grayish, opaque or translucent appearance, with in some cases a shrunken aspect and undue firmness of texture, with at points, centres of softening. If hardened, the sclerosed sections take the carmine stain deeply, but the osmic acid or hæmatoxylin stain very slightly, contrary to what holds in health. In recent cases there is only slight thickening of the neuroglia, but when the disease is advanced the trabeculæ are thick, dense, and firm, and the nerve fibres have largely disappeared. The coats of the blood vessels adjacent to the sclerosis are thickened and their lumen is narrowed. Thickening of the meninges is not uncommon, either confined to those covering the diseased portion of the cord or extending completely around it. Atrophy of the nerve roots is often appreciable by the naked eye. _Diagnosis._ This depends largely on the fact that the condition follows an acute attack of myelitis, on the supervention of muscular weakness and lack of muscular control, whenever the animal is exercised to fatigue, the morbid symptoms subsiding promptly when he is allowed to rest, the aggravation of these symptoms when the patient is blindfolded and a gradual though slow advance of the symptoms with the lapse of time. From arteritis and embolism it is to be distinguished by the absence of the local symptoms of pain and tenderness, and by the absence of pulsation in the same artery distal of the obstruction and of improvement by the lapse of time or a run at grass.