IX.] THE DYNAMICS OF LIFE. 97 



weight is transformed into the potential energy due to the 

 raised weight, and if the same musciilar energy is expended 

 without being able to raise a weight or do other external 

 work, it is transformed into heat.^ Normally, the increase 

 of temperature is not more than about 1° Fahr., and it is not 

 perhaps incredible that this should be due to the more 

 rapid chemical action that goes on in muscle when it is 

 in activity than when in repose. This heightening of 

 chemical action in muscles during activity is proved by 

 the fact that lactic acid, which is a product of their oxida- 

 tion, is found in the muscles of animals that have been 

 violently convulsed, though it is not found in muscles in 

 their normal state.^ But though chemical action may 

 account for a rise of temperature in muscle to the extent 

 of 1° Fahr. it appears altogether inadequate to account 

 for a rise of the temperature of the body to llOf ° Fahr., 

 which is more than ten degrees above its normal level; 

 and this has been observed in the convulsions of tetanus, in tetanus. 

 No conceivable increase in the rate of chemical action 

 would produce such a rise of temperature as this ; and I 

 believe it must have been caused by the transformation of 

 a portion of the stock of vital energy into heat. 



Another case of increased production of animal heat 

 which cannot be due to any increase in the rate of oxida- 

 tion or of any other chemical process, has been observed 

 in patients dying of yellow fever, when the temperature of Heat pro- 

 the body rose to the extent of 5° Fahr. in the first ten *|"°,^,'^.^* 

 minutes after death. What proves, if proof were needed, 

 that the heat could not be from any chemical source, is 

 that the capillary circulation in those cases continued for 

 an appreciable time after death, showing that putrefaction 

 coTild not have set in ; and this extraordinary production 

 of heat can, I think, only be explained by sixpposing that 

 the vital energy of the body was transformed into heat in 

 the act of dying.^ 



1 The following statements, where no other authority is given, are taken 

 from Carpenter's Human Physiology, chap. x. 

 * Carpenter's Human Physiology, p. 677. 

 3 There is an experiment of the celebrated John Hunter which is 



H 



