576 HEAT-PRODUCTION IN ACTIVE MUSCLE. 



HEAT-PRODUCTION IN ACTIVE MUSCLE. 



Method. The increased temperature of a muscle during contraction may be 

 determined either by means of delicate thermometers introduced between the 

 muscles, or thermo-electrically. The passive muscle on the opposite side of the 

 body, or the blood within a vein, will serve for purposes of comparison. As the 

 resistance to conduction in metals (platinum wire, lead strips) is increased by 

 heat, the observation may also be made in this way. 



After Bunzen, in 1805, had observed the development of heat during 

 muscular activity, v. Helmholtz demonstrated in 1848 that also ex- 

 cised frogs' muscles, tetanized for two or three minutes, exhibit a rise 

 in temperature of from 0.14 to 0.18 C. R. Heidenhain even succeeded 

 by thermo-electrical means in demonstrating an increase in temperature 

 of from 0.001 to 0.005 C. for each individual contraction. A similar 

 condition exists in the beating heart, whose temperature rises with each 

 systole. The production of heat in the muscle exhibits a latent stage, 

 which is, however, of shorter duration than the latent period of move- 

 ment. 



A contraction of a frog's muscle, weighing one gram, will produce an amount 

 of heat equal to about three microcalories, which will raise the temperature of 

 three milligrams of water from o to i C. 



The following facts have been ascertained concerning heat -produc- 

 tion: 



T . // bears a relation to the amount of work performed, (a) If the 

 muscle during contraction carries a weight that during rest extends 

 it again, it performs no work that is communicated externally. All 

 of the transformed, chemical, potential energy is, therefore, converted 

 into heat during this movement. Under these conditions the genera- 

 tion of heat corresponds with the activity; that is it increases at first 

 with the weight and the height of the lift to the maximum point , and then, 

 as the weight is further increased, the generation of heat diminishes. The 

 heat-maximum, however, is attained with a smaller weight than the 

 maximum of work. 



(6) If the muscle at the height of its contraction is relieved of its 

 weight, then it will have performed some active work communicated 

 externally. Under such circumstances the amount of heat generated is 

 less than in the previous case ; and, indeed, the amount of work performed 

 and the lesser amount of heat evolved, are the same in accordance with 

 the law of the conservation of energy. 



(c) If the same amount of work is performed in the one case by many 

 small contractions, and in the other by fewer but larger contractions, 

 the amount of heat generated is greater in the latter instance. This fact 

 indicates that large contractions are attended with a relatively greater 

 metabolism than smaller ones, and experience is in accordance with it. 

 Thus, the ascent of a tower by steps with a high tread causes much more 

 fatigue (that is requires more metabolism) than ascent by steps with a 

 low tread. 



(d) If a weighted muscle executes single contractions in succession, 

 by means of which it performs work, the amount of heat thus generated 

 is greater than if it carries the weight constantly in tetanic contraction. 

 The transition of the muscle into the shortened form thus develops a 

 greater amount of heat than the maintenance of that form. Also sum- 



