"Black leg" is a common disease of young cattle in all sections of the
country where cattle-raising is engaged in extensively. Outbreaks of the
disease are most prevalent in the early spring after the snow has melted,
and in the late summer in localities where cattle graze over the dried-up
ponds and swampy places in the pasture. The germs of black leg may be
carried from a farm where the disease is prevalent to non-infected premises
by surface water. The opening up of drainage ditches through stock-raising
communities may be followed by outbreaks of the disease.

[Illustration: FIG. 119.--Bacillus of emphysematous anthrax.]

_The symptoms_ of black leg develop quickly and may terminate fatally in a
few hours. These are general dulness, stiffness, prostration and loss of
appetite. Lameness is a prominent symptom. The animal may show a swelling
in the regions of the shoulder and hindquarters or on other parts of the
body. The swelling is very hot and painful at first, but if the animal
lives for a time, it becomes less tender, crackles when pressed on and the
skin may feel cold and leathery. Fever is a constant symptom. In the highly
acute form of the disease nervous symptoms, such as convulsions and coma,
occur.

_The tissue changes_ in the region of the swelling are characteristic. An
incision into the swelling shows a bloody, dark exudate and the surface of
the muscular tissue is dark. Frothy, bloody liquid escapes from the mouth,
nose and anus.

_The preventive treatment_ consists in thoroughly draining pastures and
yards where cattle run. This measure does not insure cattle against the
disease. Cattle that die of "black leg" should be cremated. This should be
done at the spot where the animal dies. If the carcass is moved or opened,