372 What are Animals and Plants? 



tion ' is very often nothing more than the assigning of some 

 new or unfamiHar object to a class of objects which has 

 aheady become famihar ; and our minds are so formed that 

 they feel an almost inevitable satisfaction in the reference of 

 some object or action, difficult or impossible to imagine, to a 

 class of objects or actions easy to imagine, and this whether 

 or not such reference, when closely examined, turns out to be 

 really justifiable, and therefore truly satisfactory. 



Now there is nothing so easy for us to imagine as the 

 motions of solid bodies, phenomena which appeal both to 

 sight and touch. Thus it is that (apart from scientific 

 utilities we shall shortly refer to) 'heat,' 'Hght,' 'chemical 

 phenomena,' the action of nerves and of brain cells, are 

 apt to appear easier to understand, and to be more 

 or less ' explained,' when they are spoken of as ' Modes of 

 Motion.' 



Nevertheless, such an explanation of the action of Hving 

 beings is, as we have said, shocking to common-sense, and 

 therefore, as has just been mentioned, another force was in- 

 vented to account for them, and the actions of living beings 

 have been explained as being due to the energising within 

 them of a ' Vital Force.' 



But the doctrine of the existence of any such force has 

 been more and more successfully opposed by men of science 

 on the ground that (1) living beings are not isolated pheno- 

 mena in nature, but are affected by and react upon all 

 physical forces ; (2) that no distinct evidence is forthcoming 

 of the existence of any such ' vital force ' ; and (3) that while 

 the use of such a conception in no way furthers the ends of 

 science, the mechanical conception of nature aids in the 

 discovery of natural laws, and has powerfully helped on the 

 progress of science. 



And it is true that Hving beings are/ar indeed from being 

 isolated; for the life of each of us largely consists of an 



