446 Proceedings of the Boyal Physical Society. 



XXXVIII. Synthetic Summary of the Influence of the Environ- 

 ment upon the Organism. By J. Arthur Thomson, Esq., 

 M.A., r.E.S.E. 



(Read 21st December 1887.) 



**The direct action of the medium was the primordial factor of organic 

 evolution. " — Spencer. 



All naturalists agree in interpreting life as a relation 

 between two facts, — on the one hand the plant or animal, on 

 the other the external conditions. Function is the connecting 

 link between the two facts, and is defined in general terms 

 as action and reaction between the organism and its environ- 

 ment. The organism modifies its surroundings, and is in 

 turn modified by them, and these two processes are the 

 obviously complementary and inseparable aspects of its life. 

 As Claude Bernard says, " the conditions of life are neither 

 in the organism, nor in its external surroundiDgs, but in both 

 at once." The organism, though in itself a true unity of 

 living matter, has its personal identity maintained by streams 

 of energy from without. It is unnecessary to go to the one 

 extreme of regarding the organism as an insulated unity, or 

 to the other extreme of supposing it merely a focus of ex- 

 ternal energies ; the truth of both aspects may be combined. 

 The relative constancy of the converging streams of energies 

 conditions the relative constancy of the organism, as of a 

 special wave-crest in the sea; while changes in the streams are 

 associated with corresponding changes in the organism. The 

 researches referred to below deal with such changes in the 

 external conditions, for it is only in the study of the changes 

 that we can hope to understand the relative constancy. 



2. In thus seeking to appreciate the influence of the en- 

 vironment, it is necessary — 



(1.) to catalogue and classify the various outside factors; 



(2.) to review the facts known in regard to their in- 

 fluence ; 



(3.) to distinguish the various degrees of influence ; and 



(4.) to estimate the importance of environmental in- 



fluence as a factor in organic evolution. 



