HERMANN VON HELMHOLTZ 



possible, outside the muscles of the frog, and the two 

 sets of junctions were connected with a thermal 

 galvanometer, so sensitive, that deflections equivalent 

 in thermal value to the y^Vu^h of a degree Centigrade 

 could be detected. When the muscles were caused to 

 contract, by electrically stimulating the sciatic nerve, 

 the junctions in the muscle became warmer than 

 those outside the muscle, as indicated by a deflection 

 of the needle of the galvanometer, and as the galvano- 

 meter had been empirically graduated, the actual rise 

 of temperature was at once estimated. It was thus 

 shown that a single muscular contraction would give an 

 increase of from '001 C. to '005 C., and that tetanus, 

 or cramp, lasting for two to three minutes, would 

 cause a rise of from '014 C. to *oi8 C. He failed, 

 however, to detect heat in active nerves. These 

 quantities of heat are no doubt small, but their detec- 

 tion showed that the molecular processes occurring 

 in the contracting muscle actually produce heat. 



Helmholtz also extended his observations to the 

 general phenomena of animal heat. On Lavoisier's 

 assumption that the amount of heat liberated could 

 be determined by the quantities of oxygen consumed 

 and of carbonic acid produced, it had hitherto been 

 found that there was a discrepancy between the 

 amount of heat actually given off by the body of an 

 animal in a given time and the amount to be expected 

 from calculation. The calculated amount of heat 

 was usually more than that given off the living body. 

 34 



