THE RELATION OF LIFE TO OTHER FORCES. 313 



to be used, but not by the being which laid it up. The labors of the 

 vegetable world are not for itself, but for animals. The power laid up 

 by the one is spent by the other. Hence the reason that the constant 

 change, which is so great a character of life, is comparatively but little 

 marked in plants. It is present, but only in living portions of the 

 organism, and in these it is but limited. In a tree the greater part of 

 the tissues may be considered dead; the only change they suffer is that 

 fresh matter is piled on to them. They are not the seat of any transfor- 

 mation of force, and therefore, although their existence is the result of 

 living action, they do not themselves live. Force is, so to speak, laid up 

 in them, but they do not themselves spend it. Those portions of a 

 vegetable organism which are doing active vital work which are using 

 the sun's light and heat as a means whereby to prepare building material, 

 are, however, the seat of unceasing change. Their existence as living 

 tissue depends upon this fact upon their capability of perishing and 

 being renewed. 



And this leads to the answer to the question, What is the cause of 

 the constant change which occurs in the living parts of animals and 

 vegetables, which is so invariable an accompaniment of life, that we 

 refuse the title of "living" to parts not attended by it? It is because all 

 manifestations of life are exhibitions of power; and as no power can be 

 originated by us, as, according to the doctrine of correlation of force, all 

 power is but the representative of some previous force in the same or 

 another form, so, for its production, there must be expenditure and 

 change somewhere or other. For the vital actions of plants the light and 

 heat of the sun are nearly or quite sufficient, and there is no need of 

 expenditure of that store of force which is laid up in themselves; but 

 with animals the case is different. They cannot directly transform the 

 solar forces into vital power; they must seek it elsewhere. The great 

 use of the vegetable kingdom is therefore to store up power in such a 

 form that it can be used by animals; that so, when in the bodies of the 

 latter, vegetable organized material returns to an inorganic condition, 

 it may give out force in such a manner that it can be transformed by 

 animal tissues, and manifested variously by them as vital power. 



Hence, then, we must consider the waste and repair attendant on liv- 

 ing growth and development as something more than these words, taken 

 by themselves, imply. The waste is the return to a lower from a higher 

 form of matter; and, in the fall, force is manifested. This force, when 

 specially transformed by organized tissues, we call vital. In 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 molecular 

 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 



