MUSCLE 247 



Juction of heat is necessary in warm-blooded animals to 

 maintain the temperature of the body at a level at which 

 the chemical changes essential for life are possible. 



That heat is given off by muscles in contraction is shown 

 by the fact that, after muscular exercise, the temperature of 

 the body rises for a short time. Some deHcate method of 

 measuring the temperature must be employed to demonstrate 

 heat production in single isolated muscles. The mercurial 

 thermometer is hardly sufficiently sensitive, and, therefore, 

 the thermo-electrical method is most generally employed. 

 Various forms of thermopile may be used (Appendix). 



The rise of temperature in a muscle after a single con- 

 traction is extremely small, but after a tetanic contraction, 

 lasting for two or three minutes, it is much greater. 



By the use of extremely delicate thermopiles it has been 



Fig. 129. — The continuous line shows the contraction of the heart of the 

 terrapin : the dash line the production of heat, and the dotted 

 line the temperature. 



shown that in contraction most of the heat is evolved in the 

 relaxation phase. This is more easily demonstrated in the 

 slow contraction of the heart of the terrapin than in skeletal 

 muscle. 



The above diagram shows the relation of mechanical 

 shortening to heat production (fig. 129). 



The amount of heat produced by a single isolated muscle 

 may be calculated if (a) the weight of the muscle, (6) its 

 temperature before and after contraction, and (c) the specific 

 heat of muscle, are known. 



The specific heat of muscle is slightly greater than that 

 of water, but the difference is so slight that it may be 

 disregarded. If, then, a muscle of ten grams had a tempera- 

 ture of 15° C. before it was made to contract, and a tempera- 



