274 THEORETICAL CONSIDERATIONS 



the other hand, the modification or total inhibition of any one process 

 does not necessarily indicate that the living matter has been directly 

 affected, for such a condition would result if, as in the case of the 

 resting seed, the rays destroyed an enzyme essential to the comple- 

 tion of some function. 



The broadest, and at the same time the most definite generaliza- 

 tion warranted by the work so far done is that the rays of radium 

 act as a stimulus to metabolism. If this stimulus ranges between 

 minimum and optimum points, all metabolic activities, whether con- 

 structive or destructive, are accelerated ; but if the stimulus increases 

 from the optimum toward the maximum point it becomes an over- 

 stimulus, and all metabolic activities are depressed and finally com- 

 pletely inhibited. Beyond a certain point of over-stimulus recovery 

 is impossible, and death results. 



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