MUSCULAR FORCE, ORIGIN OF. Until the year 1860 the universally accepted theory on this subject was that of Liebig. According to bim, non-nitrogenous food is consumed entirely in the production of beat; while muscular energy is due to the waste of the nitrogenous muscular tissue, and therefore of nitrogenous food. Muscular exercise should, if this were the case, cause very distinct increase in the nitrogenous excretions of the body, as well as greater elimination of non-nitrogenous substances.
But the experiments of Fick and Wisficenus, made during an ascent of the Faulhorn, led them to deny altogether the increase of excretion of nitrogen, and to come to the conclusion that the energy generated in the muscles is the result of the burning (oxida tion) of non-nitrogenous substances (fats and earbo-hydratesy, and not of the burning of the albuminous constituents of muscular tissue; and they conclude that the nitrogenous constituents of muscles are rather to be regarded as forming the machine in which these substances arc burned than as being themselves destroyed. (For a translation of their memoir, see Phil. Alitg., June, 1866, supplementary number).
Dr. Frankland (Philosophical Magazine, Sept., 1860) arrives at the conclusion that the non-nitrogenous constituents of the food, such as starch, fat, etc., are the chief sources of the actual energy, which becomes partially transformed into muscular work. He does not, however, deny to the albuminous matters a co-operation in the production of muscular power, but he regards their chief use as being to renew the muscular tissue. The muscles are thus the source both of animal heat and of muscular energy.
Dr. Parkes, in a long and careful series of experiments (see Proceedings of the Royal Society, vols. xv., page 339; xvi., page 44; xix., page 349; and xx., page 402), examined the effect of exercise, both with a non-nitrogenous and with a nitrogenous diet. He found no marked increase, but often a diminution, of the nitrogenous substances excreted during exercise,' though subsequently a slight increase took place.
Dr. Pave, in a series of elaborate experiments recorded in the Lancet (Feb., Mar:, Nov., Dec., 1876; Jan., 1877), comes to a similar conclusion. He says: "The theoretical deduction to be drawn from the investigation which has been conducted is that, although the elimination of urinary nitrogen is increased by muscular exercise, yet the increase is nothing nearly sufficient to give countenance to the proposition that the source of the power manifested in muscular action is due to the oxidation of muscular tissue."
The theory of muscular action which Dr. Parkes proposes is as follows: During action the muscles appropriate nitrogen; this act is accompanied by changes in the carbo hydrates, which lead to the manifestation of mechanical force; these changes lead to effete products (lactic acid, etc.) in the muscles, which, as appears from llanke's experi ments, stop their contraction. Then ensues an action of oxygen upon the nitrogenous framework of the muscle, and a removal of the effete products of the carbo-hydrates, so that the muscle becomes again capable of appropriating nitrogen, and of acting.
But, although some such theory as this finds favor with most physiologists, and agrees with most of the experiments on the subject, it is not universally accepted.
Dr. A. Flint of New York made observations on Weston, the American pedestrian, which seemed to show that, in his case at least, the excretion of nitrogen is very dis tinctly increased, both during and after severe muscular work. He accordingly comes to the conclusion that " the exercise of muscular power immediately involves the destruction of a certain amount of muscular substance, of which the nitrogen excreted is a measure." That is to say, he adheres to the original view of Liebig. His experi ments are described in the Journal of Anatomy and Physiology, vol. xi., page 109: and his views are developed in the same journal, vol. xii , page 91, where also numerous references are given to other works and papers on the subject.
All observers arc agreed that the amount of carbon excreted in the form of carbonic acid is very largely increased during exercise.
Besides the papers named above, the following may be consulted for a resumui of the subject: Liebig, in Riarmaceutical Journal and Transactions, 1870; Volt, in Zeitschrift far Biologie, 1870; Foster, Text-Book of Physiology, page 323.