20 THE MECHANISM OF INJURY AND RECOVERY 



The fact that in the case of Laminaria recovery may be either partial 

 or complete, according to circumstances, raises the question whether 

 this is also true of other forms. It is certainly true of all the plants 

 investigated by the writer, such as the green alga, Ulva (sea lettuce) , the 

 red alga, Rhodymenia (dulse), and the flowering plant, Zostera (eel 

 grass). It seems to be also true of frog skin as far as the experiments 

 of the writer have gone.^ In physiological literature it seems to be 

 generally assumed that when recovery occurs at all it is practically 

 complete. It is evident that partial recovery might easily be over- 

 looked except in cases where recovery can be measured with consid- 

 erable accuracy, and it seems possible that further investigation may 

 show that partial recovery is a general phenomenon. 



If we accept the conclusions stated above we are obliged to look 

 upon recovery in a somewhat different fashion from that which is 

 customary. Recovery is usually regarded as due to the reversal of 

 the reaction which produces injury. The conception of the writer 

 is fundamentally different ; it assumes that the reactions involved are 

 irreversible (or practically so) and that injury and recovery differ 

 only in the relative speed at which certain reactions take place. 



Thus in the series of reactions O^S—^A^^M—^B, if the rate of 

 0—^S becomes slower than the normal, injury will occur, while a re- 

 turn to the normal rate will result in recovery. Injury could also 

 be produced by increasing the rate of M-^B, or decreasing the rate 

 oiS^A or A-^M. 



If life is dependent upon a series of reactions which normally pro- 

 ceed at rates bearing a definite relation to each other, it is clear 

 that a disturbance of these rate-relations may have profound effects 

 upon the organism, and may produce such diverse phenomena as 

 stimulation, development, injury, and death. It is evident that such 

 a disturbance might be produced by changes in temperature^ (in case 

 the temperature coefficients of the reactions differ) or by chemical 

 agents. The same result might be brought about by physical means, 

 especially where structural changes occur which alter the permea- 

 bility of the plasma membrane or of internal structures (such as the 

 nucleus and plastids) in such a way as to bring together substances 

 which do not normally interact.^" 



^ The recovery experiments on frog skin have been few in number and were 

 devoted chiefly to the eff'ects of anesthetics. 



» Cf. Osterhout, W. J. V., J. Biol. Chem., 1917, xxxii, 23. 

 ^*0r which normally react to a lesser degree. 



