ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 8l 



the tonic condition, on the other hand, to the critical level, 

 the greater will be the excitatory overflow, and the smaller 

 the latent component. The internal and external factors 

 will thus be complementary to each other. 



On subjecting this inference to experimental demon- 

 stration by means of growth-response, I fully succeeded in 

 verifying it. According to this method of growth-response, 

 it will be remembered, the true excitatory effect is measured 

 by retardation of the normal rate of growth, the internal 

 factor of increased latent energy being represented, on the 

 other hand, by a corresponding enhancement of the rate of 

 growth. This being understood, it was found that in a 

 particular specimen of growing tissue, whose tonic condition 

 was somewhat low, the external and internal effects caused 

 by a given stimulus were in the proportion of 32 to 13-5. 

 When the tonic condition of the specimen was raised, how- 

 ever, and the same stimulus was applied, the external effect 

 was found to be enhanced to 38 at the expense of the internal, 

 which was now found to be lowered to 8*5. The sum of the 

 work done, both internally and externally, is seen to be in 

 both these cases approximately the same, being in the former 

 experiment 45'5, and in the latter 46-5. 



We have seen that, of the two antagonistic factors of 

 response, the positive will predominate if the excitability 

 of the tissue be in any way diminished. Such a loss of 

 excitability may occur in either of two ways: (i) by the 

 sub-tonicity of the tissue itself; (2) by the depression con- 

 sequent on fatigue. Under either of these conditions then 

 we may expect to obtain the exhibition of the positive effect. 



The exhibition of the positive effect under fatigue will be 

 described in the course of the next chapter. We shall here 

 consider instances in addition to those already given, of the 

 occurrence of the positive effect in a tissue which is sub-tonic. 

 We have to bear in mind that the work which incident 

 stimulus is called upon to perform is two-fold, both internal 

 and external, and that there is a certain critical excitatory 

 level, above which only is the normal responsive expression 



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