GE^'ERATION OF WARMTH DURING CONTRACTION. 75 



« 



and thus, from the strength of the current, it is possible 

 to determine the temperature of one point of contact 

 if that of the other is known. In our case, in which it 

 is not necessary to determine absolute temperatures, 

 but only to show an increase in warmth, the method is 

 more simple. It is only necessary to provide that the 

 two points of contact have the same temperatiu'e at 

 lirst, a condition which can be recognised by the absence 

 of any current, and the additional degree of warmth ac- 

 quired can then be directly calculated from the strength 

 of the current which is afterwards generated. 



Helmholtz performed the experiment by placing 

 the two thighs of a frog which had been recently killed 

 in a closed case, after he had so arranged the metals 

 w^hich were to determine the warmth that one point of 

 contact was inserted in the muscles of one thigh, the 

 other in those of the other He then waited till the 

 temperatures of both thighs became equal, so that, 

 though the metals were connected with a sensitive mul- 

 tiplier, no current was apparent. The muscles of one 

 thigh were thrown into strong tetanus by introducing 

 a suitable inductive current, while those of the other 

 thigh remained at rest. The contracted muscles then 

 became warmer and imparted their warmth to the 

 soldered metals embedded in them ; the result was an 

 electric current the strength of which was measured. 

 The increase in the warmth of the muscle, thus de- 

 termined, was about 'lo of a degree. This warmth 

 may seem slight, but it must be remembered that but 

 a small mass of muscle was treated, and that this 

 necessarily lost a considerable part of the warmth gene- 

 rated within it by radiation and by imparting it to the 

 surrounding substances. 



