ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 77 



sion. If further, the tissue, on recovery, return to its original 

 condition, then a second similar stimulus will induce the 

 same responsive expression as the first. These responses 

 will thus be uniform. But if, owing to the after-effect of 

 stimulus, the condition of the tissue itself be changed, the 

 responses will be found to exhibit either staircase increase or 

 fatigue decline, according to the particular molecular con- 

 siderations involved, which will be described in detail in the 

 following chapter. 



It will be interesting here, however, to take an extreme 

 case of a tissue in the opposite condition namely, of great 

 sub-tonicity. It is clear that since the excitability of the 

 tissue is here feeble, there will be little or no outward 

 manifestation of excitatory response. The incident stimulus 

 will thus be absorbed, and entirely held latent. And the 

 increase of internal energy thus brought about may find 

 expression mechanically by expansion, or electrically by 

 galvanometric positivity. 



In the case which we have selected, the excitability of the 

 tissue is too low for the ordinary excitatory expression to occur. 

 Hence the incident stimulus will be entirely absorbed, and 

 there will be a gain of energy without any loss. The whole 

 responsive expression will in this case consist, not of con- 

 traction but of expansion. In other words, it will be exactly 

 opposite to that which is usually consequent upon external 

 stimulus. In order to demonstrate this, I took a seedling of 

 Tamarindus indicus which had been cut ofT from its supply 

 of external energy, and was consequently sub-tonic. Owing 

 to the insufficiency of internal energy, its growth had, in 

 fact, come to a standstill. On now subjecting this seedling 

 to thermal stimulation, the absorbed stimulus raised the 

 internal energy and found expression in growth expansion. 

 We have seen that the effect of external stimulus on a growing 

 organ in normal tonic condition was the retardation or arrest 

 of growth. But here, in a tissue which is sub-tonic, we find 

 that the effect is exactly opposite. 



Without, however, taking so extreme a case, as that in 



