THE RELATION OF LIFE TO OTHER FORCES. 723 



In this instance, then, there is constant waste and repair, yet with- 

 out life. And here an objection cannot be raised, as it might be to the 

 preceding example, that both the destruction and repair come from 

 without, and are not dependent on any inherent qualities of the sub- 

 stance with which they have to do. The waste and renewal in the last- 

 named example are strictly dependent on the qualities of the chemical 

 compound which is subject to them. It has but to be placed in appro- 

 priate conditions, and destruction and repair will continue indefinitely. 

 Force, too, is manifested, but there is nothing present which can trans- 

 form it into vital shape, and so there is no life. 



Hence, our notion of the constant decay which, together with repair, 

 takes place throughout life, must be not confined to any simply mechan- 

 ical act. It must include the idea, as before said, of laying up of force, 

 and its expenditure its transformation too, in the act of being ex- 

 pended. 



The growth, then, of an animal or vegetable, implies the expenditure 

 of physical force by organized tissue, as a means whereby fresh matter is 

 added to and incorporated with that already existing. In the case of the 

 plant the force used, transformed, and stored up, is almost entirely de- 

 rived from external sources; the material used is inorganic. The result 

 is a tissue which is not intended for expenditure by the individual which 

 has accumulated it. The force expended in growth by animals, on the 

 other hand, cannot be obtained directly from without. For them a sup- 

 ply of force is necessary in the shape of food derived directly or indi- 

 rectly from the vegetable kingdom. Part of this force-containing food 

 is expended as fuel for the production of power ; and the latter is used 

 as a means wherewith to elaborate another portion of the food, and in- 

 corporate it as animal structure. Unlike vegetable structure, however, 

 animal tissues are the seat of constant change, because their object is 

 not the storing up of power, but its expenditure ; so there must be con- 

 stant waste ; and if this happen, then for the continuance of life there 

 must be equally constant repair. But, as before said, in early life the 

 repair surpasses the loss, and so there is growth. The part repaired is 

 better than before the loss, and thus there is development. 



The definite limit which has been imposed on the duration of life 

 has been already incidentally referred, to. Like birth, growth, and de- 

 velopment, it belongs essentially to living beings only. Dead structures 

 and those which have never lived are subject to change and destruction, 

 but decay in them is uncertain in its beginning and continuance. It de- 

 pends almost entirely on external conditions, and differs altogether 

 from the decline of life. The decline and death of living beings are as 

 definite in their occurrence as growth and development. Like these they 

 may be hastened or stayed, especially in the lower forms of life, by vari- 

 ous influences from without ; but the putting off of decline must be the 



