18 THE MECHANISM OF INJURY AND RECOVERY 



formed and decomposed by a series of reactions according to the 

 scheme 



We assume that in sea water the amount of M remains constant 

 because it is formed as rapidly as it is decomposed. When, however, 

 it is transferred to a solution of NaCi (or to the first of the two mix- 

 tures mentioned above) the resistance falls, because M is decomposed 

 more rapidly than it is formed. In the second mixture the resistance 

 rises, because M is formed more rapidly than it is decomposed, but 

 after a certain time the rate of formation decreases and the resistance 

 falls steadily. 



We suppose that when tissue is placed in the solution of NaCl (or 

 in the mixtures) the reactions 0—^S~*A cease. In the solution of 

 NaCl (and in the first mixture) the amount of M diminishes on ac- 

 count of the gradual exhaustion of ^ ; in the second mixture the reac- 

 tion A~^ M i?> so rapid that a temporary increase in the amount of 

 M results, but this is inevitably followed by a decrease as the supply 

 of A becomes exhausted. 



When the tissue is replaced in sea water the reactions Q—^S—^A 

 are supposed to recommence. The supply of A is therefore replen- 

 ished and the resistance will return to the normal value, provided O 

 is present in large amount and suffers practically no change during 

 the experiment. But if it should diminish by one-half as the result 

 of exposure to NaCl it could restore M to only half of its original 

 value. We may therefore regard the level to which M is restored as 

 an index of the condition of O. If we plot this level after various peri- 

 ods of exposure to the first mixture we get Curve B in Fig. 2 (and for 

 the second mixture. Curve D).^ 



If we use the term recovery for the rise of resistance which occurs 

 when tissue is transferred to sea water from certain solutions (such as 

 the first mixture) there seems to be no good reason why it should not 

 be appHed to the fall of resistance which occurs when tissue is trans- 

 ferred from certain other solutions (such as the second mixture) to 

 sea water. The amount of recovery after any given period of exposure 



^ A similar curve could be drawn for Fig. 1 but it has been omitted in order to 

 avoid confusion. 



