CHAPTER VII 



ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 



Sign of response determined by latent energy of tissue, and by intensity of 

 external stimulus Sub-tonic, normal and hyper-tonic conditions The 

 critical level Outward manifestation of response possible only when critical 

 level is exceeded Three typical cases : response greater than stimulus ; 

 response equal to stimulus ; and response less than stimulus Investigation by 

 growth-response Instance of sum of work, internal and external, performed 



Iby stimulus constant Positive response of tissues characterised by feeble 

 protoplasmic activity or sub-tonicity Enhancement of normal excitability 

 of sub-tonic tissue by absorption of stimulus. 



WE shall find, in this and succeeding chapters, that the 

 nature and intensity of response are determined not merely 

 by the intensity of stimulus, but also by the molecular con- 

 dition of the responding substance. The excitatory mani- 

 festation is dependent upon the occurrence of a particular 

 directioned molecular distortion. Hence, if by the action of 

 the stimuli of the environment, an incipient distortion in this 

 direction has already been inducecj in the tissue, the incidence 

 of even moderate stimulus will then prove sufficient to 

 precipitate visible excitatory manifestation. A tissue in this 

 condition is said to be highly excijable or fully tonic. If, on 

 the other hand, the tonic condition be less favourable, long- 

 continued stimulation will be necessary to evoke the excita- 

 tory effect. Here, during the first part of application, 

 stimulus will appear to be ineffective. As a matter of fact, 

 however, it is at work to give such a predisposition to the 

 molecules that the action of subsequent stimulus shall be 

 rendered effective. 



In the simple case in which the tonic condition is favour- 

 able, a given stimulus will induce a given responsive expres- 



