4:8 THE DATA OF BIOLOGY. 



combustion. But most likely this antithesis is not 



true even in the more restricted sense. The probability is 

 that the hydrocarbons and carbo-hydrates which, in travers- 

 ing the system, are transformed by communicated chemical 

 action, evolve, during their transformation, not heat alone 

 but also other kinds of force. It may be that as the nitro- 

 genous matter, while falling into more stable molecular 

 arrangements, generates both that molecular agitation 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 trans- 

 formed 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 tis- 

 sue-food both as material for building-up tissue and as matCr 

 rial 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, § 100) 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 

 rapidity of such re-distributions, this raised state of molecular 

 vibration is conspicuous. And we here see that this raised 

 state of molecular vibration is itself a continuous conse- 

 quence of the continuous molecular re-distributions it facili- 

 tates. The heat generated by each increment of chemical 

 change makes possible the succeeding increment of chemical 



