THERMAL AND CHEMICAL CHANGES IN MUSCLE 55$ 



than a few /u apart. This would mean an almost infinite loss of 

 heat by conduction between the two points. It is inconceivable that 

 such differences of temperature exist. It has been shown, moreover, 

 that the heat is not formed solely during the period of contraction of 

 the muscle. It is formed both during the contraction and during the 

 relaxation (Fig. 295). There is, moreover, no constant ratio between 

 the amount of work done and the amount of heat evolved. High 

 initial tension and strong excitation favour the production of heat. 



FIG. 294. DOUBLE THERMOPILE, EACH OF A PAIK OF SARTORII BEING IN CONTACT 

 WITH ONE SET OF JUNCTIONS. (A. V. Hill.) 



A, A, Junctions of iron and constantan in contact with front sartorius, M ; B, B r 

 junctions in contact with rear sartorius, M'; K is bone of pelvis held by clamp, 

 D ; 6, copper leads to galvanometer; E, electrodes only two out of four shown. 

 Arrow shows direction of current. Only six instead of twenty-four to thirty 

 junctions shown. 



An isolated frog's muscle at 15-5 C. continues for about five hour* 

 to carry on the normal oxidative processes of life, but at a declining 

 rate. This is due to the gradual exhaustion of the oxygen supply, 

 and to the gradual accumulation of waste products other than CO 2 , 

 Possibly, also, the supply of oxidizable material becomes exhausted. 



The initial process of contraction consists largely, if not entirely, 

 of the liberation of potential energy, which is manifested as " tension 

 energy " in the excited muscle. This potential energy is capable of 

 being used indifferently for the accomplishment of work or the pro- 

 duction of heat. The efficiency of the whole of the processes, in- 

 cluding those of recovery, is sometimes as high as 50 per cent. that 



