S4« MANUAL OF ELEMENTARY ZOOLOGY 



We may sum up the foregoing considerations as follows. 

 The possibly peculiar features of the living 



Summary. ,. r r Jr ,., „ , .. D 



being are of two kinds. Some of the processes 

 which constitute life — assimilation, conduction, and so 

 forth — seem at present to involve capabilities which cannot 

 be explained by the action of the forms of energy which 

 are found in lifeless matter. On the other hand, all the 

 life processes, whether they involve such capabilities or not, 

 are peculiar in that they exhibit direction towards the 

 welfare of the bodies in which they occur. Of this direction 

 the processes of development, both in reproduction and in 

 regeneration, are a special case. We have said that the 

 body is a machine. We must now recognise that it differs 

 from all other machines (i) possibly in possessing powers 

 not found elsewhere, (2) certainly in that its activity is 

 directed to its own preservation and to that of its kind. In 

 the present state of knowledge the division between living 

 things and lifeless ones is wide and clear. If each of the 

 processes of life could be paralleled in things which are not 

 alive, it would still be necessary to explain how these 

 processes came to be connected and directed as they are 

 in living beings. 



Two warnings, however, must be given lest the nature 



of these differences be misunderstood. It 

 tion" allfl ° a " must: m tne nrst place be recognised clearly 



that the powers we have mentioned do not dis- 

 pense the bodily machine from the obligation to act, like 

 other machines, in conformity with the principle of the con- 

 servation of energy. What they appear to do is to enable 

 it to effect kinds of transformation of energy which are not 

 met with elsewhere. Like a steam-engine, the body can 

 do nothing except in virtue of the energy which it obtains, 

 in the long-run, from the food which becomes its fuel. 

 It would appear, however, that, unlike the steam-engine, 

 living bodies can use their energy in ways which are not 

 possible outside themselves. Secondly, in the purposive- 

 ness of the processes of life we have a phenomenon, 

 remarkable indeed, but not necessarily incapable of 

 explanation. 



So far we have been dealing with matters of fact. The 

 existence in living beings of the peculiarities we have just 



