STRIATED MUSCLE. 79 



We see, thus, that muscular contraction (or the passage of 

 the muscle from the first to the second form) must be reck- 

 oned first among the sources of animal heat, on account of 

 the active combustion which is then produced. If, indeed, a 



into respiratory and plastic, attributing to the latter (albuminoids) 

 the source of muscular labor, could only be admitted after direct 

 proof. Reasoning first led to the belief that muscular labor, being a 

 form of heat, must derive its origin from aliments whose combus- 

 tion furnishes the greatest degree of heat, as the fats and hydro- 

 carbons. And Mayer calculated that if it was true that the muscle 

 consumes either its own substance or albuminoids (which comes to 

 the same thing) , the heat developed by the oxidation of these sub- 

 stances is so trifling that a man would have entirely consumed his 

 muscular mass after a few days' labor. 



The question could only be decided by direct experiment, and 

 the proof needed was very simple. We shall see farther on that 

 the residuum of combustion of the albuminoids is essentially con 

 stituted by the urea eliminated by the kidneys; if, during mechan- 

 ical labor, a large amount of albuminoids are consumed, there will 

 be a great increase of urea in the urine. 



After some unsatisfactory experiments by Lehmann and Speck, 

 and some, more conclusive, by Bischoff and Vogt, Fick and \Yis- 

 licenus solved the problem in a remarkable manner. These two 

 physiologists ascended, fasting, one of the high mountains of the 

 Bernese Alps, measuring carefully the quantity of urea eliminated 

 by the kidneys during and after the ascent. In the case of one of 

 them the labor developed by this ascent may be represented by 

 184 287 kilogrammetres, yet no increase in the urea was observed 

 either during or after this very severe muscular exercise. We see 

 thus that the muscle, as the source of labor or heat, consumes only 

 hydrocarbons and fats, and not albuminoids. 



To this satisfactory experiment may be added some considera- 

 tions of comparative physiology. The herbivorous animals, that 

 is, those which feed principally on hydrocarbons, are capable of 

 developing a much greater degree of force than the carnivora, 

 which are nourished by albuminoids; thus man for mechanical 

 labor makes use only of the herbivorous animals (the horse, the 

 ox). The granivorous birds are in general more active, and 

 develop more heat and labor, than the carnivorous. This fact is 

 still more striking in the case of insects: thus, among the acari 

 some live as parasites on animals, while others feed on flour or 

 sugar (for instance, Glyciphagi); the former being remarkable 

 for the slowness, and the latter for the almost incredible rapidity 

 of their movements. An experiment of this kind, in regard to 

 food, has also been made upon man. An Englishman, liarting, 

 found, after submitting to a regimen of fifteen hundred grammes 

 of meat a day, with scarcely any hydrocarbons, that he was re- 

 duced to an extreme degree of muscular weakness. 



