CLASSIFICATION OF LIVING TYPES 49 



results of our investigation go to show that the unity 

 in that conception, or rather the conception of that 

 unity, is to a considerable extent borne out by facts. 



To clear our ideas then and base a definition upon 

 a physical basis for the purposes of our classification ; 

 Life might be described as a specialised mode of 

 motion, the specialised mode of motion being, that 

 of a complex system of molecules in a dynamically 

 unstable state, so that there is a continuous or 

 continual change, or flux of its substance, between 

 the individual aggregates of molecules and their 

 surroundings. 



This definition includes everything we understand 

 by life from its physical basis and most general 

 biological signification. But it is far more general 

 than the definitions generally employed. It is more 

 general even than Herbert Spencer's definition of the 

 continuous adjustment of the internal and external 

 relations of the individual to its environment. This 

 may or may not include a radio-active atom, the 

 former certainly does not exclude it. Whence the six 

 apparent conditions laid down in the previous chapter 

 can be satisfied by it, even if far more elementary 

 phenomena are also included within its scope. 



Thus the radio-active atom, the molecules of cyano- 

 gen, the complex molecular aggregate that takes part 

 in many phosphorescent and other luminous effects, 

 form examples of that specialised unsteady state of 

 motion, which in some instances, when the environ- 

 ment in which it occurs is of a suitable nature, can 

 give rise to aggregation in some manner at present 



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