REAL SOURCE OF MOTOR POWER. 927 



Ranke and others have supposed, arrest the muscular contraction ; a period of 

 rest follows, in which the effete products are removed, and nitrogen is elimi- 

 nated ; and the muscle is once more fit for action. This view explains most 

 of the facts very well ; it is also in accordance with experience, as to the neces- 

 sity of nitrogenous food for persons engaged in prolonged muscular work ; and 

 yet it admits that the changes in the nitrogenous elements of muscle, are inad- 

 equate to produce the movement, and refers these to the chemical energy 

 evolved by some neighboring non-nitrogenous substances. 



The views of Liebig, as to the separate and exclusive sources of 

 heat and motion in the animal economy, are, therefore, controverted 

 by more recent knowledge; it is certainly disproved, that the disinte- 

 gration of muscular substance is the only source of muscular power; 

 and it is equally proved that, in Man, and probably in Omnivorous 

 animals, the oxidation of non-nitrogenous materials is its chief source. 

 But the chemical powers of the living animal economy have perhaps 

 been underrated ; and a priori theories may, in both directions, limit 

 too much our notions respecting them. Carnivorous animals, as would 

 appear from the observations of Lawes arid Gilbert on fattening ani- 

 mals, of Savory and others, upon rats and dogs fed on a flesh diet ex- 

 clusively, have the power of splitting up albuminoid bodies into fats 

 and certain nitrogenous compounds. If so, this fat on being oxidized, 

 may become the source of motor power. Besides, as albuminoid bodies 

 are undoubtedly oxidized in the body, they must furnish potential 

 energy transformable either into heat or motion. It seems impossible 

 to believe, with Dr. Frankland, that the blood only, and not the nervo- 

 muscular substance also, is oxidized in the production of muscular 

 force ; or to deny that nitrogenous substances may also yield force, as 

 well as heat. Work is well performed, for a short time, on a non- 

 nitrogenous diet, but fatigue is at last felt, and nitrogenous matter 

 must be wasted; otherwise it would not be retained in unusual quan- 

 tity, when nitrogenous food is again taken, after a temporary absti- 

 nence from it. Nitrogenous food must therefore be supplied, probably, 

 in accordance with the amount of work done. (Parkes.) A muscle 

 may be a machine, and the blood circulating through it, the fuel ; but 

 being a living tissue, it, and its nerves, and controlling nervous centres, 

 waste, or they would not become fatigued and exhausted by work. A 

 muscle probably wastes more than a machine wears. This waste may 

 depend largely on the loss of the hydrocarbons, and carbhydrates, in 

 the muscle, and the nerves, yet the more abundant nitrogenous sub- 

 stances in them must likewise participate in the exhaustive process. 

 Before, too, we accept Dr. Parkes' view as to muscular action being 

 accompanied by an absorption of nitrogenous substance, and by growth, 

 it becomes necessary to determine the amount of brain-, spinal-cord-, 

 and nerve-substance, which is consumed, or changed, in all motor acts. 

 This is probably considerable, and possibly largely affects the fatty 

 matter of these organs. Might not this oxidation, together with the 

 nutritive changes accompanying it, explain, in part, the increased evo- 

 lution of carbonic acid during exercise ? By occupying the oxygen in 

 the blood, it might also account for there being less to act upon the 

 muscular tissue. Yet, we know nothing of the amount of change in 

 the nervous substance considered separately. 



