842 OF THE STRUCTURE AND FUNCTIONS OF MUSCULAR TISSUE. 



derived from the combustion of the nitrogenous constituents of his muscles 

 or of his blood, is proved by the circumstance that the elimination of urea, 

 which may be regarded as the final product in the animal body of the de- 

 composition of the albuminoid compounds, is by no means proportional to 

 the amount offeree expended ; and secondly, by the fact that even allowing 

 a large margin for errors of calculation and experiment, the absolute quan- 

 tity of nitrogen eliminated by the body represents an amount of albuminous 

 material the combustion of which is insufficient to account for the muscular 

 force that is generated with even moderate exertion. That the oxidation of 

 the non-nitrogenous materials of the blood occurs during work, to furnish 

 the heat which the muscles transform into mechanical force, is shown first, 

 by the greatly increased amount of carbonic acid contained in the venous 

 blood of a contracting muscle, as compared with a muscle at rest (Sczelkow, 

 194) ; secondly, by the increased elimination of carbonic acid and water 

 that occurs during exercise (E. Smith, 311) ; thirdly, by the fact that in 

 some animals, as in bees (Verloren), as well as in man (Fick, Parkes) a 

 considerable amount of exertion can be temporarily undertaken on a diet 

 containing little or no nitrogen, as sugar and fat, though it has been clearly 

 shown that if the diet be exclusively confined to non-nitrogenous material, 

 weakness and weariness soon supervene, quickly followed by complete mus- 

 cular exhaustion (Hammond, Savory, Parkes). It may be remarked, also, 

 that in those nations, and in those animals, that are well supplied with ni- 

 trogenous compounds in their food, a superior physical condition is produced, 

 enabling them to maintain severe exertion for a longer period, and also to 

 exert, when occasion may require, more vigorous effort for a shorter period, 

 than those whose diet is of a poorer quality, or contains less nitrogen in an 

 easily assimilable form. The precise seat of the oxidation cannot be held 

 to be decisively ascertained, and some, but not very satisfactory, evidence has 

 been brought forward to show that it takes place within the vessels. The 

 chemical facts connected with the contraction of muscle have been ingeni- 

 ously woven by Hermann 1 into the following theory. He supposes that 

 muscle contains a store of a complex nitrogenous material in a state of solu- 

 tion. It is unstable, and in the act of disintegration develops force. The 

 products of its disintegration are, inter alia, carbonic acid, paralactic acid 

 (possibly, as Ranke believes, sugar and fat), and an albuminous compound 

 which in the living muscle is gelatinous, but soon coagulates into a solid 

 substance (Myosin). When at rest the disintegration proceeds slowly, but 

 it is rendered more energetic by elevation of temperature within certain 

 limits, and is induced instantly by certain "irritants." As the muscle-sub- 

 stance is gradually consumed by exertion, it is requisite for the maintenance 

 of its characteristic properties that a constant circulation of blood should 

 take place through its vessels, by which means not only may oxygen and 

 fresh supplies of nutritive material be brought to it, but the products of its 

 disintegration, the presence of which seriously impairs its contractile powers, 

 may be removed.' 2 The power of the muscles appears to be capable of being 



1 Griimlriss der Physiologic, 18(17, p. 226. See also Schenk, Archiv f. Exper. 

 Path., 1874, Bd. ii, p. 21. 



2 The reader will find much interesting information on the several views of the 

 origin of muscular force, with references to previous writers, in I'layfair's Essay on 

 the Food of Alan iti Relation to his useful Work, Kdinb., 18(55; Heaton's Essay on 

 the Function of the Mlood in Muscular Work, Phil. Mag., 18(17; Bonders, On the 

 Constituents of Food in their Inflation to .Muscular Work and Animal Heat, trans- 

 lated by Dr. Mo.. n>, Dublin, 18<'>C>; Parkes's Kssays on the Elimination of Nitrogen 

 by the 'Kidneys (Proceedings ,,f the Royal Society, 1807, Nos. 89 and 94) ; Proceed. 

 Roy. Soc., Lond., 1874, No". 150, and Professor Haughton's Address at the Meeting 

 of the Jiritish Medical Association, 1808. 



