162 



HABIT AND INTELLIGENCE. 



[chap. 



Voluntary- 

 action : 

 depending 



shall know, on what the difference depends between the 

 sensory and the merely reflex ganglia : in other words, 

 why it is that some ganglia become sentient when they are 

 acted on by their nerve-fibres, while others are without 

 that wondrous property. The microscope has not revealed 

 any difference between the ganglia, or between the nerve- 

 fibres, which are thus so unlike in their powers. 



Last and highest is voluntary muscular action. This, 

 also, as well as reflex and consensual action, in all pro- 

 on nervous bability depends on the stimulus of currents of nervous 

 energy acting on the ganglia which are in communication 

 with the motor nerves ; but in the case of voluntary action, 

 the exciting currents proceed, not, as in the other two 

 cases, from the outer extremities of nerve-fibres, but from 

 within the brain itseK. I shall have to say more on this 

 subject when I come to treat of Mind. 



It is to be observed that no line can be drawn between 

 consensual and voluntary action. Many actions, such as 

 closing the eyes or coughing, may be either the one or the 

 other; and an action that was at first voluntary may 

 become consensual from habit ; as, for instance, the act of 

 walking, which, though it has to be almost consciously 

 learned by the child, soon comes to be carried on in re- 

 sponse to the sensation of touching the ground with the 

 feet, without needing a fresh determination of the will at 

 every step. It is proved by the facts of instinct that many 

 actions which are voluntary in man are consensual in 

 many, if not all, of the lower animals. Thus, chickens pick 

 up grains, and ducks run to the water, the moment they 

 are out of the egg. 



We thus enumerate four kinds of motor action in organ- 

 isms, according to the way in which it is produced, as 

 follow : — 



1st. Spontaneous. 



2d. Produced by an unfelt stimulus, or reflex. 



3d. Produced by a felt stimulus, or consensual. 



4th. Voluntary. 

 It is interesting to observe how these functions are suc- 

 cessively added, the one to the other, in the ascending 



Instinct. 



Summaiy. 



