68 CROONIAN LECTURES 



that stuff are there, and indestructible and 

 inseparable. Inorganic matter and inorganic 

 force always exist, together in living things ; so 

 that, if a separable living force be also present, 

 then we must admit that two totally different 

 relations of ponderable matter and force must 

 obtain in the same matter at the same time. 



The unity of nature will at least be preserved 

 by our hesitation to admit the assumption of 

 a force capable of creation and annihilation, 

 until some very conclusive evidence is obtained 

 that there actually is in living things such a force 

 or forces capable of being separated entirely 

 from the matter of which they are made. 



Until this be proved, let us inquire how far 

 the third stage of ideas regarding the union of 

 matter and force and the principle of the con- 

 servation of energy opens new paths for inves- 

 tigation, and gives us new glimpses of truth. 



What are the actual and potential energies 

 which enter into the body ? To what motions 

 do these energies give rise there? How do 

 these motions leave the body ? 



Matters in a state of tension, and ready for 

 chemical motion, are constantly going into the 

 body in the food and air. The quantity of 



