the Phenomena of the Electric and Nervous Influences. 43 



That every voluntary motor-nervous filament forms a di- 

 stinct closed circuit. 



That every sensitive filament forms a distinct circuit. 



That every incident filament forms a distinct circuit. 



That every reflex filament forms of itself a distinct closed 

 circuit. 



That every incident filament of the sympathetic system (if 

 I may be allowed the expression), which conveys the impres- 

 sion to its centre, forms in itself a closed circuit; and lastly, that 

 every reflex sympathetic filament in proceeding from its cen- 

 tre forms a closed circuit. 



These several nerves are each of them looped at the extre- 

 mity of their course, and no doubt looped in their centre, such 

 as the spinal cord ; and it is highly probable that the mass of 

 the spinal cord is but a congeries of these loops completing the 

 circle, or at all events that the mass of the gray matter closes 

 the circuit of the several nerves leading into it. If a nerve be 

 divided all reflex action ceases, because the conditions neces- 

 sary to the production of inductive action no longer exist. 



35. Another condition necessary to galvanic induction, is 

 contiguity of the channels conveying the primary and the in- 

 duced currents. It will be found that reflex motion exists only 

 in muscles whose motor nerves are contiguous to those sensi- 

 tive or incident nerves which conveyed the impression of the 

 irritation that produced the so-called reflex motion. I might 

 venture to assert, that in most instances where reflex action is 

 produced, the nerves conveying the impression and those of 

 motion are bound up in the same sheath ; and it is probable 

 that the plexuses in the axillary and inguinal region of animals 

 are for the purpose of adjusting these nerves in their conti- 

 guous groups before their distribution to the organs. I have 

 used the term " reflex," it being a word well known as desig- 

 nating this species of involuntary motion ; but I would be in- 

 clined to prefer the expression of induced motion for all that 

 class of nervous action which proceed from the centre to the 

 periphery, excited by currents in the sensitive and incident 

 nerves proceeding from the periphery to the centre. 



36. The conditions necessary for inductive action having 

 been shown strictly to exist in nerves that produce involuntary 

 motion, it can also be demonstrated that the peculiar action 

 produced by induction occurs whenever involuntary, reflex or 

 induced motion is produced : in Section 33 it has been shown 

 that electrically induced currents are of momentary duration, 

 and of a like kind are all involuntary motions ; even tetanus is 

 a rapid series of spasmodic interrupted contractions. We have 

 also illustrations of these interrupted actions in the rhythmic 



