The early symptoms of acute pleurisy are chills, rise in body temperature, pain and abdominal breathing. The most characteristic symptom is the ridge extending along the lower extremities of the ribs (pleuritic ridge). The animal does not stand still as in pneumonia, but changes its position occasionally, its movements in many cases being accompanied by a grunt. Pressure on the wall of the chest causes the animal to flinch and show evidence of severe pain. Large animals rarely lie down. The cough is short and painful. On placing the ear against the wall of the chest and listening to the respirations, we are able to hear friction sounds. After a few days effusion occurs in the pleural cavity. Although the animal may have refused to eat up to this time, it now appears greatly relieved and may offer to eat its feed. This relief may be only temporary. If the fluid exudate forms in sufficient quantity to cause pressure on the heart and lungs and interfere with their movement, the pulse beat is weak, the respirations quick and labored, the elbows are turned out and the feet are spread apart. All of the respiratory muscles may be used. The expression of the face may indicate threatened asphyxia. We may determine the extent of the pleural exudate by auscultation. There is no evidence of respiratory sounds in that portion of the chest below the surface of the fluid. Dropsical swellings may occur on the under surface of the breast and abdomen. _In subacute cases_ evidence of recovery is noted in from four to ten days. _Acute pleurisy_ very often terminates fatally. Under the most favorable conditions, recovery takes place very slowly, sometimes extending over a period of several months. It is not uncommon for the horse to continue having "defective wind." _The treatment_ consists in good care, well ventilated quarters and careful nursing, the same as recommended in the treatment of pneumonia. At the very beginning, the pain may be relieved by the administration of small doses of morphine. If the conditions in the stable permit, a hot blanket that has been dipped in hot water and wrung out as dry as possible, may be applied to the chest wall and covered with a rubber blanket. This treatment should be continued during the first few days of the inflammation. These applications may be reinforced by occasionally applying mustard paste to the sides of the chest.