THE RELATION OF LIFE TO OTHER FORCES. 721 



the repair, force is laid up. The analogy with ordinary transmutations 

 of physical force is perfect. By the expenditure of heat in a particular 

 manner a weight can be raised. By its fall heat is returned. The molec- 

 ular motion is but the expression in another form of the mechanical. 

 So with life. There is constant renewal and decay, because it is only so 

 that vital activity can take place. The renewal must be something more 

 than replacement, however, as the decay must be more than simple me- 

 chanical loss. The idea of life must include both storing up of force, 

 and its transformation in the expenditure. 



Hence we must be careful not to confound the mere preservation of 

 individual form under the circumstances of concurrent waste and repair, 

 with the essential nature of vitality. 



Life, in its simplest form, has been happily expressed by Savory as a 

 state of dynamical equilibrium, since one of its most characteristic fea- 

 tures is continual decay, yet with maintenance for the individual by 

 equally constant repair. Since, then, in the preservation of the equilib- 

 rium there is ceaseless change, it is not static equilibrium but dynam- 

 ical. 



Care must be taken, however, not to accept the term in too strict a 

 sense, and not to confound that which is but a necessary attendant on 

 life with life itself. For, indeed, strictly, there is no preservation of 

 equilibrium during life. Each vital act is an advance towards death. 

 We are accustomed to make use of the terms growth and development in 

 the sense of progress in one direction, and the words decline and decay 

 with an opposite signification, as if, like the ebb of the tide, there were 

 after maturity a reversal of life's current. But, to use an equally old 

 comparison, life is really a journey always in one direction. It is an 

 ascent, more and more gradual as the summit is approached, so gradual 

 that it is impossible to say when development ends and decline begins. 

 But the descent is on the other side. There is no perfect equilibrium, 

 no halting, no turning back. 



The term, therefore, must be used with only a limited signification. 

 There is preservation of the individual, yet, although it may seem a 

 paradox, not of the same individual. A man at one period of his life 

 may retain not a particle of the matter of which formerly he was com. 

 posed. The preservation of a living being during growth and develop- 

 ment is more comparable, indeed, to that of a nation, than of an indi- 

 vidual as the term is popularly understood. The elements of which it 

 is made up fulfil a certain work the traditions of which were handed 

 down from their predecessors, and then pass away, leaving the same leg- 

 acy to those that follow them. The individuality is preserved, but, like 

 all things handed down by tradition, its fashion changes, until at last, 

 perhaps, scarce any likeness to the original can be discovered. Or, as it 

 sometimes happens, the alterations by time are so small that we wonder, 

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