I/O 



NATURE AND MAN. 



involuntary, and depend upon the excitation of certain states of 

 mind by external impressions, they must be considered as 

 " reflex " in the general sense of that term. 



Now the usual modus operandi of sensations is to call forth 

 ideas to the mind ; and these ideas, associated or not with emo- 

 tional states, become the subjects of intellectual processes, which 

 result at last in a determination of the will. The movements we 

 term, voluntary or volitional differ from the emotional and auto- 

 matic, in being guided by a distinct conception of the object to 

 be attained, and by a rational choice of the means employed. 

 And so long as the voluntary power asserts its due predominance, 

 so long can it keep in check all tendency to any other kind of 

 action, save such as ministers directly to the bodily wants, as the 

 automatic movements of breathing and swallowing. 



The cerebrum is universally admitted to be the portion of the 

 nervous system which is instrumentally concerned in the forma- 

 tion of ideas, the excitement of the emotions, and the operations 

 of the intellect ; and there seems no reason why it should be 

 exempted from the law of " reflex action," which applies to 

 every other part of the nervous system.* And as we have seen 

 that the emotions may act directly upon the muscular system 

 through the motor nerves, there is no a priori dithculty in believ- 

 ing that ideas may become the sources of muscular movement, 

 independently either of volitions or of emotions. — The relations 

 of these different modes of action of the nervous system, and the 

 place which this ideo-motor form of " reflex " operation will 

 hold in regard to the rest, will be made more apparent by the 



following tabular arrangement : — 



THE WILL 



Volitional Movement 



Cerebrum —> Motor Impulse N g 



Intellectual Processes'' ■) 



t t I 



i Emotions 



L-t 



Ideas 



t 



Sensations -^ Sensory Ganglia — > Motor Impulse 



t 



Impressions — ^ Spinal Cord — ^ Motor Impulse 



rt O 



< 



* To Dr. Laycock is due the credit of first extending the doctrine of reflex 

 action to the brain. 



