162 NERVOrS CORRELATION 



character. For example, the act of walking, although 

 very complex, is in a technical sense a pure reflex. This 

 means that the muscular contractions which make up the 

 act are initiated and regulated by immediate sensory 

 stimulation. The sensory stimulation which operates in 

 this particular reflex has a number of sources, the pres- 

 sure of the soles of the feet upon the ground, the muscle 

 sense aroused from the contractions of the muscles and 

 the bending of the joints, the sense of equilibrium brought 

 into play as the head swings with the motions of the 

 body, the sense of sight if one happens to be walking 

 with the eyes open, all contribute stimuli which are cor- 

 related within a part of thje central nervous system set 

 aside for that purpose and caused to discharge an accu- 

 rately timed and properly graded series of stimuli to 

 cause the muscles to perform in sequence and to the de- 

 gree that is necessary for successful walking. 



(6) Volitional. — Contrasted with an act of this sort, 

 which is purely reflex, are many activities which are 

 spoken of as voluntary, namely, as carried out by the will. 

 When a volitional act is analyzed it is found to be guided 

 by a combination of the immediate environment with 

 such associated memories as apply to the case in hand. 

 It is conceivable that a volitional act might be the result 

 wholly of memory, no immediate stimulus having any- 

 thing to do with starting it off". Yet, study of the activi- 

 ties of animals as well as our own activities shows that 

 in a vast majority of cases the acts that we call volitional 

 depend upon a combination of immediate sensory stimu- 

 lation with associated memory. Since all associations are 

 built originally upon sense impressions it is possible to 

 trace the origin of all activities back to receptors. Thus, 

 strictly speaking, the brain does not originate activity 

 but merely causes to go on to completion chains of events 

 which have their origin in sense organs. 



Instinct. — In many of the lower animals, but most 

 strikingly exemplified in insects, are to be seen numerous 



