14 COREELATION OF VITAL 



subtle and eluding. How is it possible for us to estimate the value 

 of the energy expended in regulating the nutrition of the body ? 

 How, in a motor act, shall we separate what is due to the 

 nerve and what to the muscle ? Nay, where FeeUng is aroused, 

 where Consciousness appears, how shall we estimate the equivalent 

 value of this, which each one knows in himself alone, and which 

 seems to differ so absolutely from everything else in the universe ? 

 However probable it may be that what we know as 'Sensation' 

 and 'Thought' are as truly the direct results of the molecular 

 activity of certain nerve-centres, as mechanical energy is the direct 

 result of a muscle, this cannot be proved. Still, conscious states or 

 feelings are admitted to be an appanage only of nerve actions ; and 

 their mode of appearance, their increase in intensity, and their 

 modifiability by agents modifying the nerve tissues, together with 

 the limitation by which they occur only in association with certain 

 nerve actions taking place in the highest and most complex of an 

 animal's Nerve Centres — all these facts harmonise with the notion 

 that they are in some way an actual outcome of such Nerve Actions, 

 no more capable of being dissevered from the physical conditions 

 on which they depend, than is Heat to be dissevered from its 

 physical conditions. Matter and force are inseparable — neither 

 can exist alone. But to show how these particular motions in 

 Nerve Tissue arise which underlie Conscious States, and how they 

 again subside into mere ordinary nerve actions, must, from the very 

 nature of the problem, ever remain insoluble. 



Having briefly glanced at these higher manifestations of life 

 taking place in the bodies of animals, and having indicated how 

 intimate are the relations existing between such higher manifesta- 

 tions and the physico-chemical processes ever going on in their 

 various organs during the assimilation of food, we must now, in 

 our attempt to form an estimate of the nature of life and of living 

 matter, look at the simpler problems presented by plant life. 



Plants, in fact, are the active agents ever ministering to the 

 wants of animals. They, in fashioning their own structures, are 

 continually giving birth to organic substances which are to con- 

 stitute the materials necessary for the maintenance of animal 

 life. Thus Dumas in an interesting little work by himself and 

 Boussingault on "The Chemical and Physiological Balance of 

 Organic Nature " (1844) says : — 



" M. Boussingault has demonstrated that plants in full growth 



