that muscles deprived of their natural innervation could be kept tit for work provided they were electrically excited at sufficiently brief intervals; an experiment which found an important application in surgery and neuropathology.
Even in the midst of health unused muscles pine away, or become pale and powerless, like the ear-muscles of most men. In general, the redness of muscles is related to greater strength in consequence of frequent exertions. Herr Ranvier showed that the red and pale muscles occurred together in rabbits and rooks; that they were distinguished by their structure and by the time required for contraction without its being possible to decide that one set worked more than the other, and without any clew being given to the object of this disposition. Little is known of the microscopic qualities of used and unused muscles. In contrast with the muscles of fattening cattle, working cattle have thicker primitive bundles and coarser sarcolemma, the latter determining the lesser nutritive value of the flesh. According to Herr Virchow's terminology, nutritive stimulation has also taken place. In muscles falling away through disuse, as the waste progresses a fatty metamorphosis sets in, against which, as is well known, its ceaseless activity does not protect the heart-muscle. Muscular contraction is accompanied by chemical changes. The blood flows darker from tense than from resting muscles; they consume more oxygen and form more carbonic acid. An acid permanently reddening litmus is set free in them. Their watery constituents and the amount of substances soluble in alcohol increase in them, while the amount of substances soluble in water diminishes—probably because glycogen is consumed in the contraction. The albuminous constituents remain about the same, yet the derivatives of albumen known as the flesh bases appear to be richer. That to the last hard-working muscle, the heart, is for this reason a mine of such bodies to the chemist; and the flesh of a fox that had been shot was found by Liebig to be ten times richer in creatine than that of a captive fox. We are, unfortunately, still very far from understanding the connection of these various processes and their relation to muscular contraction, that is, to the interchange of isotropic and unisotropic substances in the muscular fibers, and to the transformation of mechanical, thermic, and electric forces. We only know that there is involved an increase and modification of a process of change that was already going on during rest, particularly of the oxidation of nitrogenous substances, by which, in addition to mechanical labor-service, an apparent surplus of heat is developed. Even the muscles at rest are a seat of respiration and the development of heat in animal bodies. The muscle acts very much like the reserve-locomotive that stands ready for use on the switch, which is all the time burning a little fuel and can be attached to a train or sent to help a disabled engine at any instant, but which requires, in connection with the greater display of force it is to make, a greater consumption of material and expenditure
