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. 
Tf 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 
