RESPONSE 



IN THE 



LIVING AND NON-LIVING 



OHAPTEE I 



THE MECHANICAL RESPONSE OF LIVING SUBSTANCES 



Mechanical response Different kinds of stimuli Myograph Character- 

 istics of response-curve : period, amplitude, form Modification of 

 response-curves. 



ONE of the most striking effects of external disturbance 

 on certain types of living substance is a visible change 

 of form. . Thus, a piece of muscle when pinched con- 

 tracts. The external disturbance which, produced this 

 change is called the stimulus. The body which is thus 

 capable of responding is said to be irritable or excit- 

 able.; A stimulus thus produces a state of excitability 

 which may sometimes be expressed by. change of form. 

 Mechanical response to different kinds of stimuli. 

 This reaction under stimulus is seen even in the lowest 

 organisms ; in some of the amoeboid rhizopods, for 

 instance. These lumpy protoplasmic bodies, usually 

 elongated while creeping, if mechanically jarred, con- 

 tract into a spherical form. If, instead of mechanical 



B 



