PEOXIMATE DErmiTION OF LIFE. 61 



[t includes all organic changes, alike of the viscera, the 

 imbs, and the brain. It excludes tlie great mass of inor- 

 ganic changes ; which display little or no co-ordination. By 

 :naking co-ordination the specific characteristic of vitality, 

 it involves the truths, that an arrest of co-ordination is 

 ieath, and that imperfect co-ordination is disease. ]\Iore- 

 Dver, it harmonizes with our ordinary ideas of life in its dif- 

 ferent gradations : seeing that the organisms which we rank 

 IS low in their degree of life, are those which display but 

 little co-ordination of actions ; and seeing that from these up 

 to man, the recognized increase in degree of life corresponds 

 with an increase in the extent and complexity of co-ordina- 

 tion. But, like the others, this definition includes too much ; 

 for it may be said of the Solar System, with its regularly- 

 recurring movements and its self-balancing perturbations, 

 that it, also, exhibits co-ordination of actions. And how- 

 ever plausibly it may be argued that, in the abstract, the 

 motions of the planets and satellites are as properly compre- 

 liended in the idea of life, as the changes going on in a 

 motionless, uusensitive seed ; yet, it must be admitted that 

 they are foreign to that idea as commonly received, and 

 as here to be formulated. 



It remains to add the definition since suggested by Mr. 

 G. H. Lewis — " Life is a series of definite and successive 

 changes, both of structure and composition, whicli take place 

 within an individual without destroying its identity." The 

 last fact which this statement has the merit of bringing into 

 view — the persistence of a living organism as a Mhole, in 

 spite of the continuous removal and replacement of its parts 

 — is important. But otherwise it may be argued, that since 

 changes of structure and composition, though probably the 

 muses of muscular and nervoiis actions, are not the muscular 

 and nervous actions themselves, the definition excludes the 

 more visible movements with which our idea of life is most 

 associated ; and further, that in describing vital changes as 

 a series, it scarcely includes the fact that many of them, as 



