DISEASES OF MUSCLES - the diseases of muscular structure are not numerous, or of much importance : those chiefly concern us, in medical practice, which lead to paralysis, more or less complete. One of the most common is that which has been already traced in connection with lead poisoning (Chap. VL, Div. I., § 8). It is in great measure limited to the extensors of the forearm, and is especially recog nized by the blue line round the gums, which can always be traced when the system is impregnated with the mineral. Another condition, which is perhaps of greater importance, is that in which the true muscular ftbre becomes replaeA by fat ; fatty degenera tion is very frequently discovered in the walls of the heart, rendering its action feeble, and materially shortening existence by its effects on the circulation. In the voluntary muscles the same change 'is occasionally observed ; and in' the absence of direct evidence of its existence it may be extremely difficult to determine whether the resulting paralysis be caused by want of muscular power or of nervous energy. The only rule that can be applied to distinguish them is derived from the distribution of the nervous system : when the disease le confined to a nerve, the paralyzed muscles all derive their energy from the same source ; when situated in the central organs, the muscles which are supplied by distal nerves on the same side of the body are always involved in paralysis affecting those which receive their nerves from a point nearer to the brain ; but in paralysis caused by disease of muscle, the same law does not hold good. Atrophy
of muscle is a constant consequence of loss of nervous energy, and the causes of fatty degeneration are yet so little understood that the state of the muscle itself cannot be relied on in diagnosis.
The muscles are constantly involved in cellular inflammation, and, when suppuration follows, the fibres are bathed in pus, which burrows among their structures. Occasionally the fleshy belly of the muscle becomes the site of small abscesses, but inflamma tion of the fibre apart from that of the investing sheath of areolar tissue is unknown.