40 RESPONSE IN THE LIVING AND NON-LIVING 
a minute, instead of one, while the stimuli were 
maintained at the same intensity as before. It will be 
noticed (fig. 20, 6) that these responses appear much 
feebler than the first set, in spite of the equality of 
stimulus. An inspection of the figure may perhaps 
throw some light on the subject. It will be seen that 
when greater frequency of stimulation was introduced, 
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 new stimulus, with 
its opposing impulse, was received. 
There is thus a diminution of height 
in the resultant response. The origi- 
nal rhythm of one minute was now 
restored, and the succeeding curves 
(fig. 20, c) at once show increased 
Fic. 21.—Faticue Iv response. An analogous instance may 
CELERY 
Vibration of 30° at inter. be cited in the case of muscle re- 
Ore pene ae Bare sponse, where ‘the height of twitch 
diminishes more rapidly in proportion as the excitation 
interval is shorter.’ ! 
From what has just been said it would appear 
that one of the causes of diminution of response, or 
fatigue, is the residual strain. This is clearly seen 
in fig. 21, in a record which I obtained with celery- 
stalk. It will be noticed there that, owing to the 
imperfect molecular recovery during the time allowed, 
the succeeding heights of the responses have under- 
gone a continuous diminution. Fig. 22 gives a 
' Biedermann, Joe. cit. 
