74 CROONIAN LECTURES 



Whether animal heat arises from nervous 

 force or from chemical action has been a point 

 as disputed as whether voltaic electricity arose 

 from metallic contact or from chemical action. 



The dispute is ended in both instances by 

 the admission of the doctrine of the conserva- 

 tion of energy. 



If the animal heat comes from nervous force, 

 or the electricity from metallic contact, then 

 what is the equivalent of potential energy that 

 gives these their actual energy ? Unless the 

 creation of force be assumed, the equivalent in 

 actual or potential energy must be forthcoming. 



In the case of animal heat, it may be said 

 that the nervous force comes from an equiva- 

 lent energy of nutrition ; but then the further 

 question must be answered, Whence does this 

 energy of nutrition come ? And this brings us 

 ultimately to the chemical force which gives 

 the potential energy to the matter that enters 

 the body. This is the prime origin of the 

 motion which we call animal heat. 



The different kinds of apparatus or organs 

 which the animal possesses for the conversion 

 of energy determine in what form of motion 

 the expenditure of energy can take place. 



