

CHEMICAL AND MECHANICAL ENERGY. 395 



the same as the initial. The nature of this relation is set forth in the 

 second law of thermodynamics. It is such that, unless a very high 

 estimate be taken of the difference of temperature which in muscular 

 contraction can exist between A and B, i.e. between the source of heat 

 and its environment, the quantity of work resulting from the heat 

 transmitted would be a small fraction only of the quantity actually pro- 

 duced by the combustion of an amount of material of corresponding 

 heat value. Thus, if muscle could be made the medium of a thermo- 

 dynamic process, i.e., could be made to do work at the expense of heat 

 transmitted through it from outside, the quantity of heat transformed 

 into work would bear so small a proportion to the quantity transmitted, 

 that no comparison could be made between the hypothetical experiment 

 and what actually happens in contracting muscle. 



Such a hypothetical process as is described in the following lines, is sug- 

 gested by Fick : 



A muscle is extended by a weight, at a temperature of 20 C., and then 

 warmed to 30 C. It shortens as soon as it is allowed to do so, and lifts the 

 weight. It is then made to do further work, by gradually unloading it at this 

 temperature until the extending weight = 0. The muscle is next cooled to 

 20 C., so that it reassumes its unextended length at that temperature. Work 

 is then done upon it by extending it gradually, until the extending weight is 

 of the original amount. 



The muscle is again warmed to 30, and so the cycle recommences. 

 There is therefore in each repetition of the process a gain of external 

 mechanical work, the amount of which is in accordance with the second 

 thermodynamic law. 



This law may be expressed as follows : In every thermodynamic cyclical 

 process, the heat value of the work Q, which can be produced by the trans- 

 lation of a given quantity of heat Q v from a warmer to a colder body, depends 

 (1) on the absolute temperature of the medium T, i.e., the temperature at 

 which the process takes place, and (2) on the difference of temperature 

 between A and B (T l - T 2 ). 1 Consequently, unless it is possible to suppose 

 the existence of very large differences of temperature in the environment of the 

 acting parts of muscular substance, the doing of work in muscular contraction 

 cannot be regarded as a thermodynamic process. 



The reader will find in Engelmann's Croonian Lecture, 2 his solution 

 of this problem. He contends that a rise of temperature of the whole 

 substance of the contracting muscle, amounting to j^zr" C., would involve 

 a very high temperature of the chemically active particles, the number of 

 which he estimates to be exceedingly small. The objection that the high 

 temperature required is incompatible with life, he meets on the same ground, 

 namely, the extremely small proportion to the whole of the part in which 

 this high temperature exists. In the same lecture, experiments were adduced 

 which seemed to give support to a thermodynamic theory of muscular con- 

 traction. Of these the most important related to the work which can be 

 got out of either soaked fiddlestrings or caoutchouc, by warming these sub- 

 stances. The method is as follows : 



1 The formula by which this is expressed is 



2 T l 



If the difference between the value of T and that of T \ or T 2 is relatively small, the right 



T T Q 



side of the equation approximates to ^-= - so that the value ^- comes to depend on the 



difference of temperature between A and B. In the case now in question, Q must always be 

 extremely small as compared with $1- 



2 Proc. Roy. Soc. London, vol. Ivii. pp. 411-433. 



