MUSCULAR FORCE, ORIGIN or. This sub ject has occupied the attention of physiologists for many years. and numerous theories have been offered to explain the phenomena of muscular energy. The older observers. represented by Liebig. held that nitrogenous food went to build up and maintain muscular tissue and that energy was evolved in the splitting up (or oxida tion) of this class of food. the waste being repre sented in the excreted urea. The non-nitrorenou, food, (carbohydrates or starches, and fats), on the other hand. were supposed to be entirely de voted to the production of heat. Muscular work should therefore cause a distinct increase in the elimination of circa. But this theory is invali dated by the fact that the excretion of urea doe, not keep pace with the production of energy. Later observers have taken the opposite view, that force is generated by the oxidation of non nitrogenous that the nitrogen con stituents of muscle are rather to be looked upon as forming a part of the machine in which the former substancos are burned than as con stituting the fuel themselves.
It has been suggested by lie•man that muscular activity depends upon the splitting up and sub sequent re-formation of a complex nitrogenous body which he calls inogen. From the decom
position of this body there result carbon dioxide, sareolactic acid. and a gelatine-allmminous body. Of these the carbon dio\ idle is carried away by the blood. and the aeid and the albuminous at least in part, gee to rebuild the isogon. The other of which the Mogen is formed are supplied by the blood. Of these materials oxygen and some carbohydrate substance form a part. The decomposition takes place both in resting and active muscle, but is much greater in the latter•. This theory eertain known of muscular metabolism: first. that muscle absorbs oxygen and gives off carbon dioxide dur ing both rest and activity. and that increased exchange of these gases takes place during the latter condition; that this process is attendi"d by the production of heat ; and that muscle during rest produces nitrogenous crystallizable sub• "lamps such as kreatin from the metabolism go ing on constantly during life.
For a full diseussion of this subject. see Textbook of Phy.sioloqv (New York. Imes), and Kirke. Handbook of Thysioloqy (Philadelphia, 1901?). See also article' l'nyst• ()tout%