394 



THE PROPERTIES OF STRIPED MUSCLE. 



of muscular structure. The mechanical effects, although the consequence 

 rather than the concomitant of the chemical change, follow it instantan- 

 eously and invariably. What further happens depends upon mechanical 

 conditions, in relation to which three cases may be distinguished. If 

 (Case 1) the muscle is prevented from shortening, heat is produced m 

 quantity equal to the heat value of the material disintegrated. If (Case 

 2) the muscle is allowed to do external work, e.g. in lifting a weight, the 

 energy so used is transferred to the weight, and lost ; but if (Case 3) the 

 weight after being lifted is allowed to fall, that energy is returned to 

 the muscle at the moment of its relaxation, and manifests itself by pro- 

 ducing in it an amount of heat which is the equivalent of the potential 

 energy immediately before transferred to the weight. Consequently, the 

 eventual result in Cases 1 and 3 is of the same kind. In both, the first 

 mechanical result is the appearance of tension ; in Case 1, potential 

 mechanical energy is transformed directly into heat ; in Case 3, it is not 

 transformed until a certain proportion of it has undergone translation 

 and re translation. 



The chemical change which, as has been stated above, precedes all 

 others in the response of a muscle to stimulation, is an oxidation. This 

 does not necessarily mean that the chemical energy which is concerned 

 in the combination of oxygen atoms with those of carbon and hydrogen, 

 is directly transformed into the mechanical energy which manifests 

 itself in muscular effort. It is primd facie quite as reasonable to 

 suppose that muscle in doing work may act after the manner of a thermo- 

 dynamic machine, such as a steam-engine ; i.e., that it may first produce 

 heat by oxidation, and then use that heat in the doing of work. If this 

 is so, we have to suppose that between the initial stage of chemical 

 change and the manifestation of potential mechanical energy in the form 

 of tension, there is an intermediate stage or phase in which the whole of 

 the energy concerned in the process becomes kinetic, as heat ; in other 

 words, that between chemical attraction and mechanical tension, there is 

 a thermogenetic link in the chain of events, so that the immediate 

 agent in the production of the mechanical response is heat, not chemical 

 attraction. 



The doctrine set forth above was first enunciated in 1845 by J. K. 

 Mayer, x in the treatise which was the foundation of all that we know as 

 to the relation of heat and work in the living organism. It was not until 

 1882 that the objections to it were clearly stated by Fick 2 in the book 

 already so often referred to, and, more at length, in his " Medical Physics." 

 These are as follows : In every thermodynamic machine, i.e. in every 

 machine in which work is produced as in the steam-engine at the 

 expense of heat, the process by which this is effected consists in the 

 translation of heat from a body of higher temperature A, to a body of 

 lower temperature B, under such conditions that a certain part of the 

 heat so translated is converted into work. The utmost quantity of work 

 so producible can be determined with absolute certainty, provided that 

 the quantity of heat transmitted, the temperature of A and B, and that 

 of the medium of transmission, are known, and that the process is a 

 " cyclical " one, i.e., that the final state of the medium of transmission is 



'"Die organische Bewegung in ihrera Zusammenhang mit dem Stoffwechsel," 

 Heilbronn, 1845. 



"Meehaniselie Arbeit., u.s.w.," S. 154, 158; " Medizinische Phvsik," 1885, Aufl. 3, 

 S. 206. " 



