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 a visible form. In order to study these 

 we have to use an altogether independent method, the 

 method of electric response. 



1 Biedermann, Electro-physiology, p. 59. 



