80 THE DATA OF BIOLOGY. 



and that imperfect co-ordination is disease. Moreover, it 

 harmonizes with our ordinary ideas of life in its different 

 grades; seeing that the organisms which we rank as low in 

 their degrees 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-ordinations. But, 

 like the others, this definition includes too much. 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 however plausibly it 

 may be argued that, in the abstract, the motions of the 

 planets and satellites are as properly comprehended in the 

 idea of life as the changes going on in a motionless, unsensi- 

 tive 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. Lewes — " Life is a series of definite and successive 

 changes, both of structure and composition, which take place 

 within an individual without destroying its identity." The 

 last fact which this statement brings into view — the persis- 

 tence of a living organism as a whole, in spite of the con- 

 tinuous removal and replacement of it§ parts — is important. 

 But otherwise it may be argued that, since changes of struc- 

 ture and composition, though concomitants of muscular and 

 nervous actions, are not the muscular and nervous actions 

 themselves, the definite excludes the more visible move- 

 ments 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 Nutrition, Circula- 

 tion, Respiration, and Secretion, in their many subdivisions, 

 go on simultaneously. 



Thus, however well each of these definitions expresses the 

 phenomena of life under some of its aspects, no one of them 

 is more than approximately true. It ma}^ turn out that to 

 find a formula which will bear every test is impossible. 



