_First Aid Rule 1.--Provide large pitcher of hot water and large pitcher of cold water and basin. Hold joint over basin; pour hot water slowly over joint. Return this water to pitcher. Pour cold water over joint. Return water to pitcher. Repeat with hot water again, and follow with cold. Continue this alternation for half an hour._ _Rule 2.--Put to bed, with hot-water bottles about joint, and wedge immovably with pillows._ _Rule 3.--When tenderness and heat subside, strap with adhesive plaster in overlapping strips._ =Conditions, Etc.=--This condition, which may affect almost any freely movable joints, as the knee, elbow, ankle, and hip, is commonly caused by a wrench, blow, or fall. Occasionally it comes on without any apparent cause, in which case there is swelling and but slight pain or inflammation about the joint. We shall speak of synovitis of the knee ("water on the knee"), as that is the most common form, but these remarks will apply almost as well to the other joints. In severe cases there are considerable pain, redness and heat, and great swelling about the knee. The swelling is seen especially below the kneepan, on each side of the front of the joint, and also often above the kneepan. Frequently the only signs of trouble are swelling with slight pain, unless the limb is moved. =Treatment.=--If the knee is not red, hot, or tender to the touch, it will not be necessary for the patient to remain in bed, but when these symptoms are present a splint of some sort must be applied so that the leg is kept nearly straight, and the patient must keep to his bed until the heat, redness, and tenderness have subsided. In the meantime either an ice bag, hot poultice, cloths wrung out in hot water, or a hot-water bag should be kept constantly upon the knee. A convenient splint consists of heavy pasteboard wet and covered with sheet wadding (or cotton batting) shaped and affixed to the back of the leg, from six inches below to four inches above the joint, by strips of adhesive plaster, as shown in the illustration, and then by bandage, leaving the knee uncovered for applications. A wooden splint well padded may be used instead.