26 THE ORIGIN OF LIFE 



flux ceases, the organism as an organism may be 

 considered to have lost the property of vitality, even 

 if the constituent parts of which it is composed be 

 living. The crystal may be made up of living 

 particles, and yet as an organism it may be dead. 

 What then are the points which must be considered in 

 the definition of life ? Here we must pause awhile ; 

 and reflect not merely upon that life around us, upon 

 the qualities which are essential to it as life, and 

 which we should expect to find associated with 

 simpler types of life if they should be discovered ; 

 but upon those other qualities that, though essential 

 to the simplest forms of life already known, may be 

 merely accidents ; and the result only of their rela- 

 tively great complexity. We may formulate six points 

 in the processes that generally constitute vitality. 



(1) Living matter, it is generally supposed, must 

 contain protoplasm. It invariably is composed of 

 highly complex compounds of carbon, oxygen, hydro- 

 gen and nitrogen. It also contains sulphur, phos- 

 phorus, iron, aluminium and some other elements, 

 constituting protein, only obtained from living^matter, 

 whilst water is the chief constituent of protoplasm, 

 likewise apparently universal in existing types. 



(2) Metabolism is essentially a process taking 

 place in all living as distinct from dead matter. This 

 is more to the point if we are to deal with possible 

 forms of life. The disintegration or decomposition 

 which results from oxidation on the one hand with a 

 waste product carbonic acid, together with re-integra- 

 tion by the intus-seption or absorption of new matter. 



