38 RESPONSE IN THE LIVING AND NON-LIVING 



dissimilation of tissue by stimulus. And till this waste 

 is repaired by the process of building-up or assimilation, 

 the functional activity of the tissue will remain below 

 par. There may also be an accumulation of the 

 products of dissimilation 'the fatigue stuffs' and 

 these latter may act as poisons or chemical depressants. 



In an animal it is supposed that the nutritive blood 

 supply performs the two-fold task of bringing material 

 for assimilation and removing the fatigue products, 

 thus causing the disappearance of fatigue. This ex- 

 planation, however, is shown to be insufficient by the 

 fact that an excised bloodless muscle recovers from 

 fatigue after a short period of rest. It is obvious that 

 here the fatigue has been removed by means other than 

 that of renewed assimilation and removal of fatigue 

 products by the circulating blood. It may therefore 

 be instructive to study certain phases of fatigue 

 exhibited under simpler conditions in vegetable tissue, 

 where the constructive processes are in abeyance, and 

 there is no active circulation for the removal of fatigue 

 products. 



It has been said before that the E.M. variation caused 

 by stimulus is the concomitant of a disturbance of the 

 molecules of the responsive tissues from their normal 

 equilibrium, and that the curve of recovery exhibits 

 the restoration of the tissue to equilibrium. 



No fatigue when sufficient interval between successive 

 stimuli. We may thus gather from a study of the 

 response-curve some indication of the molecular distor- 

 tion experienced by the excited tissue. Let us first 

 take the case of an experiment whose record is given 



