Degenerative changes affecting nerves, as in other tissues, occur and
more or less locomotory impediment will follow--this depending upon the
nerve or nerves affected and the nature of such involvement. Tumors may
surround nerves and eventually the nerve so exposed becomes implicated
in the destructive process. Before degenerative changes take place in
the nerve substance, in such cases, pressure may completely paralyze a
nerve when it is so situated. Melanotic tumors in the paraproctal tissue
in some cases, because of the large size of the new-growths, cause
paralysis of the sciatic nerve. The author has seen one case of brachial
paralysis occasioned by an enormous development of fibrous tissue
involving the structures about the ulna.


AFFECTIONS OF BLOOD VESSELS.

Lameness caused by disturbances of circulation may be due to structural
affection of vessels, or functional disorders of the heart, and in some
instances, a combination of these causes may be active.

Direct involvement of vessels is the commoner form of circulatory
disturbance which occasions lameness, and the most frequent cause is of
parasitic origin. Sclerostomiasis with attendant arteritis, thrombus
formation and subsequent lodgement of emboli in the iliac, femoral, or
other arteries, causes sufficient obstruction to prevent free
circulation of blood, and the characteristic lameness of thrombosis
results.

Indirect injury to vessels may occur because of contused wounds and
subsequent inflammation of tissues supplied by such vessels. If the