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 
