THE RE- ACTIONS OF ORGANIC MATTER ON FORCES. 45 



animals to live and generate heat while consuming matter that 

 is almost exclusively nitrogenous, to say nothing of the con- 

 stant relation above shown between functional activity and the 

 evolution of heat, suffices to prove that the nitrogenous com- 

 pounds forming the tissues are heat-producers, as well as the 

 non- nitrogenous compounds circulating among and through 

 the tissues. But it is possible that this antithesis is not 



true even in the more restricted sense. It seems quite an 

 admissible hypothesis that the hydro-carbons and oxy-hydro- 

 carbons which, in traversing the system, are transformed by 

 communicated chemical action, evolve during their transform- 

 ation, not heat alone, but also other kinds of force. It may be 

 that as the nitrogenous matter, while falling into more stable 

 molecular arrangements, generates both that molecular agi- 

 tation called heat, and such other molecular movements as are 

 resolved into forces expended by the organism ; so, too, does 

 the non-nitrogenous matter. Or perhaps the concomitants of 

 this metamorphosis of non-nitrogenous matter, vary with the 

 conditions. Heat alone may result when it is transformed 

 while in the circulating fluids , but partly heat, and partly 

 another force, when it is transformed in some active tissue that 

 has absorbed it : just as coal, though producing little else but 

 heat as ordinarily burnt, has its heat partially transformed into 

 mechanical motion if burnt in a steam-engine furnace. In 

 such case, the antithesis of Liebig would be reduced to this ; 

 • — that whereas nitrogenous substance is tissue-food both as 

 material for building-up tissue and as material for its function; 

 non-nitrogenous substance is tissue-food only as material for 

 function. 



There can be no doubt that this thermal re-action which 

 chemical action from moment to moment produces in the body, 

 is from moment to moment an aid to further chemical 

 action. We before saw (First Principles, § 103) that a state 

 of raised molecular vibration, is favourable to those re-dis- 

 tributions of matter and motion which constitute Evolution. 

 We saw that in organisms distinguished by the amount and 



