VARIOUS TYPES OF RESPONSE 



83 



Fig. 42. — Different phases 

 in the fatigue-reversal 

 in plant. 



relaxation, not at first sight very different from the response- 

 curve due to a single stimulus. There would nevertheless be 

 an actual difference, inasmuch as the resulting contraction 

 under tetanisation would, on account of additive effect, be 

 greater than that caused by a 

 single stimulus. After the ap- 

 parent recovery, due to fatigue- 

 reversal under tetanisation, how- 

 ever, the excitability, as already 

 shown, is temporarily abolished ; 

 whereas after the normal re- 

 covery from a single stimulus, 

 excitability is fully restored. 



The typical case, the detailed 

 consideration of which led us to these conclusions, was 

 that of a plant which was in a somewhat sub-tonic con- 

 dition. Had the plant been in the optimum condition 

 to start with, then following the same line of reasoning 

 we should expect that the curve of tetanisation would be 

 modified in a definite way. Referring back to fig. 35, which 



gives successive records 

 of a highly excitable 

 specimen, we find in 

 this instance that the 

 very first stimulus 

 evoked the maximum 

 response, and that the 

 subsequent responses ex- 

 hibited fatigue. There 

 is not here, to begin 

 with, any staircase effect, 

 nor are the contractions 

 additive, the initial response being the greatest possible. 

 On increasing the frequency of stimulation we should, after 

 the first maximum response, obtain the phasic variation due 

 to fatigue. The successive contractile responses would thus 

 appear smaller and smaller, their respective recoveries being 



Fig. 43. — Fatigue-reversal in Mi- 

 mosa. Lower record shows 

 response under single stimulus ; 

 upper figure exhibits response 

 under continuous stimulation. 



