96 ORGANISM AND ENVIRONMENT 



also its characteristic activities and relations to exter- 

 nal environment. The life of the organism may be 

 modified, it is true ; but in the modification it retains all 

 its essential characteristics, so that its identity is un- 

 mistakable. It persists actively, and not merely pas- 

 sively. Without active adaptation everything would 

 tend to go from bad to worse, as in the case of an 

 untended machine. 



If the internal environment is interfered with, as by 

 loss of material or the introduction of foreign or super- 

 fluous material, the occurrence of adaptive changes 

 is evident. If the structural elements of the body are 

 interfered with, as in local injuries or infective attacks, 

 processes of repair soon manifest themselves at the 

 damaged point : the leaky and paralysed blood-vessels 

 become functionally competent again : exuded material 

 is absorbed ; and the altered and functionally abnormal 

 tissue elements and nerve-endings return to a normal 

 condition. We are gradually coming to realise how 

 intensely delicate is the adjustment of immediate 

 internal environment and organised structure involved 

 in the existence of normal conditions, and the more we 

 realise this the more significant appears the process of 

 recovery or adaptation. Another point with regard to 

 this process is that if injury has not gone too far the 

 restored tissues have become more resistant. It is, for 

 instance, a well-known fact that the blisters and other 

 signs of local injury produced by unaccustomed hard 

 use of the hands or feet are no longer produced after 

 "hardening" by practice. The tissues have become 

 adapted to the new conditions, and the adaptation is 



