494 HEAT-FORMATION IN AN ACTIVE MUSCLE. 



heat galvanometer. Of course, when the two muscles are at the same temperature, the needle 

 of the galvanometer is stationary ; but, if one muscle is made to contract, or is tetanised, then 

 an electrical current is set up which deflects the needle ( 208, B). Lujankow has, by means of 

 a delicate thermometer placed between the thigh muscles of a dog, estimated the rise of tempera- 

 ture under different conditions of the muscle, while the latter was still in situ and intact] 



The following facts have been ascertained with regard to the development of 

 heat : 



1. Relation to Work. It bears a relation to the amount of work. 



(a) If a muscle during contraction carries a weight which extends it again during 

 rest, no work is transferred beyond the muscle ( 300). In this case all the 

 chemical potential energy during this movement is converted into heat. Under 

 these circumstances, the amount of heat evolved runs parallel with the amount of 

 work done, i.e., it increases as the load and the height increase up to a maximum 

 point, and afterwards diminishes as the load is increased. The heat-maximum 

 is reached with a less load sooner than the work-maximum (Heidenhain). 



(b) If, when the muscle is at the height of its contraction, the load be removed, 

 then the muscle has produced work referable to something outside itself ; in this 

 case the amount of heat produced is less (A. Fick). The amount of work produced, 

 and the diminished amount of heat formed, when taken together, represent the 

 same amount of energy, corresponding to the law of the conservation of energy. 



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

 contractions, and in another by fewer but larger contractions, then, in the latter 

 case, the amount of heat is greater (Heidenhain and Naivalichin). This shows that 

 larger contractions are accompanied by a relatively greater metabolism of the mus- 

 cular substance than small contractions, which is in harmony with practical experi- 

 ence ; thus the ascent of a tower with steep high steps causes fatigue more rapidly 

 (metabolism greater) than the ascent of a more gentle slope with lower steps. 



(d) If the weighted muscle executes a series of contractions one after the other, 

 and at the same time does work, then the amount of heat it produces is greater than 

 when it is tetanic, and keeps a weight suspended. Thus, the transition of the 

 muscle into a shortened form causes a greater production of heat than the mainten- 

 ance of this form. 



2. Relation to Tension. The amount of heat evolved depends upon the tension 

 of the muscle ; it also increases as the muscular tension increases {Heidenhain). If 

 the ends of a muscle be so fixed that it cannot contract, the maximum of heat is 

 obtained (Beclard), and this the more quickly the more rapidly the stimuli follow 

 each other (Fick). Such a condition occurs during tetanus, in which condition the 

 violently contracted muscles oppose each other, and very high temperatures have 

 been registered by Wunderlich ( 213, 7), while the same is true of animals that 

 are tetanised (Leyden). Dogs kept in a state of tetanus by electrical stimulation 

 die, because their temperature rises so high (44 to 45 C.) that life no longer can 

 be maintained (Richet). In addition to the formation of heat, there is a consider- 

 able amount of acid, and of alcoholic extractives produced in the muscular tissue. 



3. Relation to Stretching. Heat is also evolved during the elongation or 

 relaxation of a contracted muscle, e.g., by causing a muscle to contract without the 

 addition of any weight, and loading it when it begins to relax, whereby heat is 

 produced (Steiner, Schmulewitsch, and Westerman). If weights be attached to a 

 muscle by means of an inextensible medium, and the weights be allowed to fall 

 from a height so as to give a jerk to the muscle, then an amount of heat equivalent 

 to the work done by the drop, is set free in the muscle (Fick and Danilewsky). 



4. The formation of heat diminishes as the muscular fatigue increases. 



5. In a muscle duly supplied with blood, the production of heat (as well as the 

 mechanical work) is far more active than in a muscle whose blood-vessels are 

 ligatured or its blood-stream cut off. Recovery takes place more rapidly and corn- 



