4 RESPONSE IN THE LIVING AND NON-LIVING 
insects to those of tortoises and hibernating dormice.’ ! 
Differences in form and amplitude of curve are well 
illustrated by various muscles of the tortoise. The 
curve for the muscle of the neck, used for rapid with- 
drawal of the head on approach of danger, is quite 
different from that of the pectoral muscle of the same 
animal, used for its sluggish movements. 
Again, progressive changes in the same muscle are 
well seen in the modifications of form which consecutive 
muscle-curves gradually undergo. In a dying muscle, 
for example, the amplitude of succeeding curves is con- 
tinuously diminished, and the curves themselves are 
elongated. Numerous illustrations will be seen later, of 
the effect, in changing the form of the curve, of the 
increased excitation or depression produced by various 
agencies. 
Thus these response records give us a means of 
studying the effect of stimulus, and the modification of 
response, under varying external conditions, advantage 
being taken of the mechanical contraction produced in 
the tissue by the stimulus. But there are other kinds 
of tissue where the excitation produced by stimulus is 
not exhibited in avisible form. In order to study these 
we have to use an altogether independent method, the 
method of electric response. 
’ Biedermann, Electro-physiology, p. 59. 
