CHAPTER LXIII 



THE PRODUCTION OF THERMAL AND CHEMICAL CHANGES 



IN MUSCLE 



THAT muscular exercise produces warmth is a familiar observation^ 

 For this reason, hard muscular exercise is uncongenial on a very hot 

 day, but is resorted to when the temperature is low, since, under 

 these conditions, even the habitual loafer is often constrained to 

 beat his arms across his chest or stamp violently to keep his feet 

 warm. It is somewhat difficult to show by means of the mercurial 

 thermometer the development of heat during the contraction of the 

 excised muscle, even when a very sensitive thermometer is inserted 

 between the muscles of the thigh, and the sciatic plexus stimulated. 

 It has been calculated that during a tetanus of two to three minutes r 

 duration the temperature of a frog's muscle rises on an average- 

 about 16 C. 



Two 

 Couples. 



FIG. 293. SINGLE-PAIR THERMOPILE CONNECTED TO GALVANOMETEK. 



The production of heat can not only be shown but measured by 

 means of a thermopile. If a thermopile (Fig. 293) be placed between 

 the calf muscles of a resting limb of a frog, and another between the 

 calf muscles of a limb which is made to contract -\ and the two thermo- 

 piles be then connected with a galvanometer, it will be found that 

 contraction liberates sufficient heat to cause a deflection of the gal- 

 vanometer needle. When both sets of muscles are at rest, no de- 

 flection takes place. For accurate work, special forms of apparatus 

 are used (Fig. 294). 



The muscle fibre has been regarded as a heat engine. It has been 

 suggested that the contraction is produced by the production of hMt 

 in the locality of the fibril, which contracts under the influence of heat. 

 Such a conception is erroneous. The muscle is rather to be regarded 

 as a chemical machine working at constant temperature. It has been 

 calculated that to behave as a heat machine it would be necessary to 

 keep up a temperature difference of 100 C. at two points not more- 



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