SO COMPARATIVE ELECTRO-PHYSIOLOGY 



(1) That when the tonic condition or the excitability of 

 the tissue is low, the predominant effect will be the positive. 

 This has been shown during the course of the present chapter 

 in the case of a very sub-tonic tissue of Tamarindus indicus, 

 where the positive or growth-expansion effect was initiated 

 by the action of stimulus. 



(2) That when the sub-tonicity of a tissue is not very 

 great, incident stimulus will at first give the positive effect of 

 an enhanced rate of growth. But with the absorption of the 

 stimulus itself, the tonic condition of the tissue will be raised, 

 and we shall then obtain the true excitatory reaction of con- 

 traction and retardation of growth. Thus, in this intermediate 

 case, the positive response will be seen to pass into normal 

 negative. 



(3) And, lastly, that when the tonic condition is already 

 high, the excitatory negative response will predominate and 

 we shall obtain normal contractile response. Both this and 

 the previous intermediate cases are illustrated by the experi- 

 ment described on Crinum lily. It was there seen that the 

 first effect of incident light was positive, the tissue being 

 sub-tonic ; subsequently, the tonic condition being raised, 

 this response was converted into the excitatory negative. 

 And on renewed application of stimulus thereafter the 

 immediate response continued to be negative. 



The fact that by means of growth-response, it is possible 

 to obtain indications of the external and internal work per- 

 formed by absorbed stimulus, enables us to demonstrate a 

 proposition of great importance, that, namely, under certain 

 conditions, the sum of the work done, internally and 

 externally, by a given stimulus, is constant. This will be the 

 case where there is little or no dissipation of energy in the 

 course of transformation. In considering the question of the 

 relative proportions of the incident stimulus utilised for in- 

 ternal and external work respectively, we find it clear, from 

 considerations already adduced, that the lower the tonic con- 

 dition the greater will be the proportion of stimulus held 

 latent for the performance of internal work. The nearer is 



