288 PROF. J. C. BOSE ON ELECTRIC RESPONSE IN 
stimulus is kept constant. It appears as if the molecular 
sluggishness of the tissue was in these cases gradually removed 
by stimulation and the increased response resulted from increased 
molecular mobility. 
Fatigue—The E.M. variation caused by stimulus is the con- 
comitant of a disturbance of the molecules of the responsive 
tissue from their normal equilibrium. The curves of recovery 
exhibit the gradual restoration of molecular equilibrium. Let 
us examine the record of an experiment given below, where 
successive stimuli were at first applied at intervals of one minute. 
It will be seen from the four curves in the first part (fig. 10) 
that there is a complete recovery of the tissue one minute 
after the application of the stimulus. The molecular condition 
Fig. 9. 
Appearance of fatigue in plant under 
shortened period of rest. 
‘* Staircase” response. 
is exactly the same at the end of the recovery as at the 
beginning of stimulation ; the second and succeeding response- 
curves therefore are exactly similar to the first, provided sufficient 
interval in each case has been allowed for complete recovery: 
The rhythm was now changed and stimuli of the same 
intensity as before applied at intervals of half a minute, instead 
of one. It will be noticed that these responses in the second part 
appear much feebler than those in the first set, in spite of the 
equality of stimulus. An inspection of the figure will throw 
some light on the subject. It will be seen that when greater 
frequency was iutroduced, the tissue had not yet had time to effect 
complete recovery from previous strain; the molecular swing 
towards equilibrium had not yet abated when the next stimulus 
