44 Mr. M. Roberts on the Electric and Nervous Influences. 



pulsation of the heart, the action of the alimentary canal, the 

 ducts of glands, and, in short, in most of the muscular con- 

 tractions of the organic life. 



37. When speaking of these as " reflex actions," I do not 

 in using their term follow the theories of either Prochaska or Dr. 

 Marshall Hall*, who have classified these motions under this 

 head : so far from agreeing with Dr. Marshall Hall in consi- 

 dering the spinal cord as the seat of the power of reflex action, 

 I believe it merely closes the circuit of the nerves; and when we 

 find reflex action suspended, from injury to the spinal cord, it 

 is not that the seat of power has been destroyed, but that the 

 closed circuit (as explained in sect. 34-) has been broken, and 

 that the spinal cord is not more essential than any other part 

 of the circuit to the production of induced motion. 



38. A case of pure induction of one nerve upon another, and 

 this attended with the peculiar phasnomena of an induced ac- 

 tion produced by the annihilation of the primary current (sect. 

 33), may be shown by a simple experiment : — Place a piece of 

 zinc upon the tongue and a piece of silver between the upper 

 gums and the upper lip ; turn the eyes towards a dark place ; 

 then, while the metals are in this position, bring their contigu- 

 ous extremities together : at the moment of contact a bright 

 momentary flash of light will be perceived; continue the con- 

 tact, and the sensation of light ceases ; but separate the metals, 

 and now a bright flash of light is again perceived at the instant 

 of separation. Here then we have an excitement of the gusta- 

 tory branch of the fifth pair which induces an action upon the 

 optic nerve, all sensation in which appears to us as light, But 

 it is worthy of observation, that this induced action is only at 

 the first moment of irritation of the gustatory nerve ; for al- 

 though the contact of the metals is continued, and consequently 

 a galvanic current is constantly circulating through this 

 nerve, yet no light is perceived ; but separate the metals, we 

 then stop the current of electricity, and at this very moment 

 another flash is seen. What can be more analogous, (may 

 I not say identical?) than these nervous phaenomena with the 

 case of electric induction in sect. 33 ? it cannot be said that this 

 is only an effect of the irritation of the optic nerve by the cur- 

 rent of galvanism ; for were this the case, the sensation of light 

 would be continuous during the passage of the electric current ; 

 whereas we find it apparent only at the moments of making 

 and breaking contact; and beside, the galvanic current is not 

 applied to the optic nerve; indeed, we have a flash when the 



* On Dr. M. Hall's theory of the reflex action, see Phil. Mag. S. 3. 

 vol. x. p. 51. — Edit. 



