INTRODUCTION 19 



regarded as due to the reversal of the reaction which 

 produces injury, the conception here developed is funda- 

 mentally different. It assumes that the reactions in- 

 volved are irreversible (or practically so) and that 

 injury and recovery differ only in the relative speed at 

 which certain processes take place. The reasons for 

 this are fully explained in the following pages. 



The experiments of the writer lead to the view that 

 life depends upon a series of reactions which normally 

 proceed at rates bearing a definite relation to each other. 

 If this is true it is clear that a disturbance of these rate- 

 relations may have a profound effect upon the organism, 

 and may produce such diverse phenomena as stimulation, 

 development, injury, and death. Such a disturbance 

 might be produced by changes of temperature (if 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 permeability of the plasma 

 membrane or of internal structures (such as the nucleus 

 and plastids) in such a way as to bring together sub- 

 stances which do not normally react. 



Throughout these investigations the aim has been to 

 apply to the study of living matter the methods which 

 have proved useful in physics and chemistry. In this 

 attempt no serious difficulty was encountered after ac- 

 curate methods of measurement had been devised: nor 

 does there seem to be any real obstacle to an extensive 

 use of methods which lead biology in the direction of the 

 exact sciences. 



It is evident from what has been said that we may 

 investigate such fundamental conceptions as vitality, in- 



