Motor 



impulse 



from 



here 



Sensation 

 received 

 here 



Vif 



automatic, as is much of the activity of 

 other species. But while reflexes are in- 

 separable from human conduct, they are 

 not the distinctive characteristic of our 

 behavior. For each reflex is a segment, or 

 fraction, which we are able to study by 

 itself. What we learn from these frag- 

 ments does not necessarily tell us that 

 the organism always acts as a whole. Or 

 that the activity of the organism is always 

 in relation to a complex situation, not 

 merely a simple response to a single 

 stimulus. 



There are mechanical elements in hu- 

 man action, but life is more than the sum 

 of these elements. Beyond these reflexes, 

 there are high degrees of intelligence, 

 high skills in adjustment, high levels of 

 imagination, initiative and ingenuity. It 

 is these that distinguish the animal with 

 the modern brain from all other species. 



Efierent 

 nerve — 



\fferent 

 -nerve 



How Do Nerves Receive Different 

 Kinds of Stimuli? 



General Sensitiveness and Special Sen- 

 sitiveness^ The naked protoplasm of 

 various small plants and of the ameba 

 and other protozoa seems to be equally 

 sensitive to many different kinds of 

 stimuli or disturbances. The protoplasm 

 reacts to mechanical pressure or direct 



Stimulus here 



BEHAVIOR LIMITED BY NERVE CONNECTIONS 



If the afferent nerve of the arm or leg is cut, 

 one might move the limb freely, but could not 

 feel any stimuli that it might receive from the 

 outside. He could walk so long as the efFerent 

 nerves were intact. If the efferent nerve were 

 cut, he could feel pain or tickling in his hands 

 or feet, but could not move a limb 

 ^See Nos. 6, 7, and 8, pp. 299 and 300. 

 284 



