120 THE NEW PHYSIOLOGY. 



adaptation — a continuous struggle for the realisation of 

 organic order. 



These adaptive changes are no mere " functional " 

 adaptations : they are also structural, and modern 

 physiology shows clearly that the distinction between 

 structural and functional change in a living organism 

 is illusory, and never stands examination. To explain 

 the adaptive changes which are constantly occurring 

 everywhere in living organisms — for instance, reproduc- 

 tion of lost or injured parts, or those marvellous functional 

 adaptations which modern surgery has learnt to take 

 such striking advantage of, the mechanistic theory is 

 forced to assume the existence of absolutely endless 

 subsidiary reproductive and compensatory mechanisms 

 in the body. Such assumptions are just as grotesque 

 as the old <; box-within-box " theory of reproduction. 



If the disturbing factor in the environment is passing, 

 and of ordinary occurrence, the adaptive change simply 

 restores the previous normal. But when the disturbing- 

 factor is unusual, or lasting, something more than a 

 return to the previous normal occurs : for we then observe 

 what is ordinarily recognised as adaptation. Common 

 examples of this are the physiological adaptations which 

 occur in learning some new operation, in training for 

 hard physical exertion, in resisting infection or poisons, 

 in becoming acclimatised to the shortage of oxygen at 

 high altitudes, or in learning to digest new kinds of food. 

 The new organic experiences involved leave their mark 

 behind in the form of definite adaptations, involving 

 not merely functional, but also structural change in 

 the organism. 



What distinguishes adaptations from other changes 



