158 INJURY, RECOVERY, AND DEATH 



There seems to be no doubt that the behavior of the 

 tissue is such as to indicate an underlying mechanism 

 which is the same in all cases. ^^ We have assumed that 

 this mechanism consists in the production and decompo- 

 sition of a substance, M, the amount of which, in the mix- 

 tures, depends largely on a compound Na4XCa formed 

 by the combination of Na and Ca with a constituent X 

 of the protoplasm. It is not necessary to discuss these 

 assumptions more fully at present. But it may be 

 pointed out that two things seem to be fairly well estab- 

 lished; (1) a consistent mechanism underlies the entire 

 behavior of the tissue, and (2) its operation can be pre- 

 dicted with a fair degree of accuracy by means of the 

 equations which have been developed. The predictive 

 value of these equations may be regarded as permanently 

 established, since it does not depend on our views regard- 

 ing the underlying assumptions. 



The results of these experiments may be summarized 

 as follows: 



1. The equations which serve to predict the injury of 

 tissue in 0.52 M NaCl and in 0.278 M CaCla and its sub- 

 sequent recovery (when it is replaced in sea water) also 

 enable us to predict the behavior of tissue in mixtures of 

 these solutions, as well as its recovery in sea water after 

 exposure to mixtures. 



2. The reactions which are assumed in order to 

 account for the behavior of the tissue proceed as if they 



" This is shown, for example, by the fact that the rapidity of permanent 

 injury (as observed after replacement in sea water) corresponds through- 

 out with the rate of death, and that the rate of change of M corresponds 

 throughout with the rate of change of 0, S and A. In other words if we 

 change the solution in such a way as to increase (or decrease) one of 

 the reactions on which the resistance depends we simultaneously increase 

 (or decrease) all the others in a definite and predictable manner. 



