XXIX.] THE PHYSIOLOGY OF MIND. 31 



currents of sensation, while now they are excited by 

 currents of thought. 



In an exactly similar way, the same action may be at The same 

 one time consensual and at another time voluntary. All action may 

 muscular action is produced by nerve-currents in the motor time con- 

 nerves ; the action of the motor nerves and of the muscles ^^"sual 



at another 



which they direct is just the same in voluntary as in con- voluntary, 

 sensual action ; it is only the stimulus, or exciting cause according 

 of the motor currents, that differs : in consensual action *° !:^^ 



. nature 



the motor nerve is excited to act by a current of sensation ; of the 

 in voluntary action it is excited to act by a current of ®*™"^'^^" 

 thought. Thus, for instance, the sensation of a flash of 

 light flowing in from the optic nerve may determine a 

 motor current which will cause the eyelids to close, with- 

 out the action of will, or even the production of conscious- 

 ness. This is consensual action ; but the eyelids may also 

 be stimulated to close by a determination of will ; in this 

 case the exciting ciirrent is not a current of sensation, but 

 a current of thought. I do not, however, suppose that the Thought 

 nerves of thought act directly on the motor ganglia ; I thf inotor 

 believe the nerves of thought, in producing voluntary ganglia 

 action, act on the motor ganglia, not directly but through the nerves 

 the nerves of will. There are anatomical reasons for this °^ ^^^'• 

 belief I have endeavoured to show how there are two 

 distinct sets of cerebral nerves, which may be respectively 

 identified as the nerves of consciousness and the nerves of 

 thought; and I believe the nerves of will may also be 

 identified.^ As already stated, it is now believed that the 

 pair of ganglia called the corpora striata really constitute 

 the nervous centre for consensual and voluntary motion. 

 They are connected with the ganglionic substance of the 

 cerebrum by thick strands of nerve-fibres, and all analogy Position of 

 is in favour of the belief that these are the nerves of will ; ^^® "7^*^^ 



, „, , of will. 



just as the fibres that connect the sensory ganglia with the 



1 The whole of what I have said on the physiological theory of voluntary 

 action is taken in substance from Carpenter's Human Physiolot^y. I 

 think, though I cannot be certain, that Dr. Carpenter would agree with 

 what I have advanced concerning the physiological theory of consciousness 

 and thought. 



