The skin is moist, to a certain degree, at all times in a healthy horse. This moisture is not in the form of a perceptible sweat, but it is enough to keep the skin pliable and to cause the hair to have a soft, healthy feel. In some chronic diseased conditions and in fever, the skin becomes dry. In this case the hair has a harsh feel that is quite different from the condition observed in health, and from the fact of its being so dry the individual hairs do not adhere to one another, they stand apart, and the animal has what is known as "a staring coat." When, during a fever, sweating occurs, it is usually an indication that the crisis is passed. Sometimes sweating is an indication of pain. A horse with tetanus or azoturia sweats profusely. Horses sweat freely when there is a serious impediment to respiration; they sweat under excitement, and, of course, from the well-known physiological causes of heat and work. Local sweating, or sweating of a restricted area of the body, denotes some kind of nerve interference. Swellings of the skin usually come from wounds or other external causes and have no special connection with the diagnosis of internal diseases. There are, however, a number of conditions in which the swelling of the skin is a symptom of a derangement of some other part of the body. For example, there is the well-known "stocking," or swelling of the legs about the fetlock joints, in influenza. There is the soft swelling of the hind legs that occurs so often in draft horses when standing still and that comes from previous inflammation (lymphangitis) or from insufficient heart power. Dropsy, or edema of the skin, may occur beneath the chest or abdomen from heart insufficiency or from chronic collection of fluid in the chest or abdomen (hydrothorax, ascites, or anemia). In anasarca or purpura hemorrhagica large soft swellings appear on any part of the skin, but usually on the legs, side of the body, and about the head. Gas collects under the skin in some instances. This comes from a local inoculation with an organism which produces a fermentation beneath the skin and causes the liberation of gas which inflates the skin, or the gas may be air that enters through a wound penetrating some air-containing organ, as the lungs. The condition here described is known as emphysema. Emphysema may follow the fracture of a rib when the end of a bone is forced inward and caused to penetrate the lung, or it may occur when, as a result of an ulcerating process, an organ containing air is perforated. This accident is more common in cattle than it is in horses. Emphysema is recognized by the fact that the swelling that it causes is not hot or sensitive on pressure. It emits a peculiar crackling sound when it is stroked or pressed upon.