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.

Wounds of the skin may be of importance in the diagnosis of internal
disease. Wounds over the bony prominence, as the point of the hip, the
point of the shoulder, and the greatest convexity of the ribs, occur
when a horse is unable to stand for a long time and, through continually
lying upon his side, has shut off the circulation to the portion of the
skin that covers parts of the body that carry the greatest weight, and
in this way has caused them to mortify. Little, round, soft, doughlike
swellings occur on the skin and may be scattered freely over the surface
of the body when the horse is afflicted with urticaria. Similar
eruptions, but distributed less generally, about the size of a silver
dollar, may occur as a symptom of dourine, or colt distemper. Hard
lumps, from which radiate welt-like swellings of the lymphatics, occur
in glanders, and blisterlike eruptions occur around the mouth and
pasterns in horsepox.

THE ORGANS OF CIRCULATION.

The first item in this portion of the examination consists in taking the
pulse. The pulse may be counted and its character may be determined at
any point where a large artery occupies a situation close to the skin
and above a hard tissue, such as a bone, cartilage, or tendon. The most
convenient place for taking the pulse of the horse is at the jaw. The
external maxillary artery runs from between the jaws, around the lower
border of the jawbone, and up on the outside of the jawbone to the face.
It is located immediately in front of the heavy muscles of the cheek.
Its throb can be felt most distinctly just before it turns around the
lower border of the jawbone. The balls of t