THE MECHANICAL RESPONSE 3 
direction, say to the right. 
depends on the amount of contraction. 
The extent of this pull 
A band of 
paper or a revolving drum-surface moves at a uniform 
speed at right angles to the direction of motion of the 
writing lever. When the muscle recovers from the 
stimulus, it relaxes into its origmal form, and the writing 
point traces the recovery as it 
moves now to the left, regaining 
its first position. A curve is thus 
described, the risimg portion of 
which is due to contraction, and 
the falling portion to relaxation 
or recovery. The ordinate of the 
. 
ed 
curve represents the intensity of 

response, and the abscissa the time 
(fig. 1). 
Fig. 1.—Mecuanicat LEvER 
RECORDER 
The muscle M with the attached 
Characteristics of the response- 
curve: (I) Period, (2) Amplitude, 
(3) Form.—Just as a wave of sound 
is characterised by its (1) period, 
(2) amplitude, and (3) form, so 
may these response-curves be dis- 
tinguished from each other. As 
regards the period, there is an 
bone is securely held at one 
end, the other end being con- 
nected with the writing lever. 
Under the action of stimu- 
lus the contracting muscle 
pulls the lever and moves 
the tracing point to the right 
over the travelling recording 
surface P. When the mus- 
cle recovers from contrac- 
tion, the tracing pointreturns 
to its original position. See 
on P the record of muscle 
curve. 
enormous variation, corresponding to the functional 
activity of the muscle. For instance, in tortoise it may 
be as high as a second, whereas in the wing-muscles of 
many insects it is as small as 51, 
‘It is probable that a continuous graduated scale might, 
part of a second. 
as suggested by Hermann, be drawn up in the animal 
kingdom, from the excessively rapid contraction of 
B 2 
