74 Royal Institution. 



ments, fibres and ganglionic corpuscles. Nerve-fibres are either 

 sensory or motor, and the activity of any one fibre does not influence 

 another. But when nerve-fibres come into relation with ganglionic 

 corpuscles, the excitement of a sensory nerve gives rise to that of a 

 motor nerve, the ganglionic corpuscles acting in some way as the 

 medium of communication. The "grey matter" which occupies 

 the middle of the spinal marrow has long been known to be the 

 locality in which the posterior roots, or sensory fibres, of the nerves 

 of the body, and the anterior roots, or motor fibres, come into relation 

 with ganglionic corpuscles ; and as the channel by which, in what 

 are called reflex actions, the activity of the sensory nerves is con- 

 Terted into excitement of corresponding motor nerves. The precise 

 modus operandi of the grey matter has been much disputed, but 

 the recent researches of Wagner, Bidder, Kupfer, and Owsjannikow, 

 throw a great light upon, and vastly simplify the whole problem. 

 It would appear that all nerve-fibres are processes of ganglionic 

 corpuscles ; that, in the spinal cord, the great mass of the grey 

 matter is nothing but connective tissue, the true ganglionic corpus- 

 cles being comparatively few, and situated in the anterior horns of 

 the grey substance ; finally, it would seem that no ganglionic cor- 

 puscle has more than five processes : one, which becomes a sensory 

 fibre and enters the posterior roots of the nerves ; one, a motor 

 fibre which enters the anterior roots ; one, which passes upward to 

 the brain ; one, which crosses over to a ganglionic corpuscle in the 

 other half of the cord ; and perhaps one establishing a connexion 

 with a ganglionic corpuscle on the same side. 



It is impossible to overrate the value of these discoveries ; for if 

 they are truths, the problem of nervous action is limited to these 

 inquiries : (a) What are the properties of ganglionic corpuscles ? 

 (0) What are the properties of their two, or three, commissural pro- 

 cesses ? For we are already pretty well acquainted with the properties 

 of the sensory and motor processes. 



A short account was next given of the physical and physiological 

 phsenomena exhibited by active and inactive nerve ; and the phee- 

 nomena exhibited by active nerve were shown to be so peculiar as 

 to justify the application of the title of " nerve-force " to this form 

 of material energy. 



It was next pointed out that this force must be regarded as of 

 the same order with other physical forces. The beautiful methods by 

 which Helmholtz has determined the velocity (not more than about 

 80 feet in a second in the frog) with which the nervous force is 

 propagated were explained. It was shown that nerve-force is not 

 electricity, but two important facts were cited to prove that the 

 nerve-force is a correlate of electricity, in the same sense as heat 

 and magnetism are said to be correlates of that force. These facts 

 were, first, the "negative deflection" of Du Bois Raymond, which 

 demonstrates that the activity of nerve aifects the electrical rela- 

 tions of its particles ; and secondly, the remarkable experiments 

 of Eckhard (some of which the speaker had exhibited in his Ful-- 

 ]pnm course), which proved that the transmission of a constant 



