18 INJURY, EECOVERY, AND DEATH 



environment are fairly uniform in their electrical resis- 

 tance, so that we may speak of a normal degree of 

 resistance as indicating a normal condition. If the plant 

 is injured and the resistance falls, we may consider 

 that the loss of resistance gives a measure of the amount 

 of injury. This enables us to place the study of injury 

 upon a quantitative basis. As the result of this we are 

 able to formulate a definite conception of the mechanism 

 of recovery. We find that if injury in a solution of NaCl 

 amounts to 5% the tissue recovers its normal resistance 

 when replaced in sea water. But if the injury amounts 

 to 25% recovery is incomplete: instead of returning to 

 the normal the resistance rises to only 90% of the 

 normal. The greater the injury the less complete 

 the recovery. When injury amounts to 90% there is 

 no recovery. 



This is of especial interest, since in physiological 

 literature it seems to be generally assumed that when 

 recovery occurs it is always complete, or practically so, 

 as if it obeyed an "all or none" law. But it is evident 

 that partial recovery may be easily overlooked unless 

 accurate measurements can be made. This fact may serve 

 to illustrate the importance of quantitative methods in 

 the study of fundamental problems. 



The significance of such methods is further shown 

 by the fact that they have led to the development of 

 equations which enable us to predict with a satisfactory 

 degree of accuracy the recovery curves which are ob- 

 served under a great variety of conditions. 



As the result of these investigations we are led to 

 look upon recovery in a somewhat different fashion from 

 that which is customary. While recovery is usually 



