228 ELECTRO-PHYSIOLOGY CHAP. 



by a striking preponderance of electromotive force (Kiihne and 

 Steiner, 2) : 



Cat 



Do 



Ea 



Duck 



Lobster 



ig 

 bbit . 



0-018 Dan. 

 0-018-0-021 Dan. 

 0-020-0-028 Dan. 

 0-024 Dan. 

 0-048 Dan. 



In the non-medullated olfactory nerve of the pike, which is 

 of approximate diameter with the frog's sciatic, Kiihne and 

 Steiner found an E.M.F. of O'0215-O'OlOo Dan., while in the 

 frog's sciatic it was only 0'002 0'006 Dan. In any case these 

 figures show the E.M.F. of the non-medullated olfactory nerve of 

 pike to be greatly in excess of that in medullated frog's nerves. 

 The difference is more than half. The medullated optic nerve 

 of the pike, which has a far larger diameter than the olfactorius, 

 alone approaches the lowest figure (O'OIOO Dan.) given for the 

 latter. The cause of this striking difference between medullated 

 and non-medullated nerve is, according to Kiihne, " either that 

 the specific E.M.F. is greater in non-medullated than in medullated 

 nerve, or that the medulla of medullated nerve is per se electric- 

 ally inactive, electromotive force being confined to the axis- 

 cylinder; so that similar cross-sections of medullated and non- 

 medullated nerve would not correspond in electromotive condition, 

 and medullated nerve would only exhibit the same electromotive 

 force as non-medullated nerve, when its anatomical cross- section 

 exceeded that of the latter to the extent occupied by the medulla 

 in the section" (Kiihne and Steiner, I.e. p. 160). 



The electrical reaction of the slender, non-medullated con- 

 nective nerves of Anodonta (3) also points to the conclusion 

 that the electromotive activity of medullated nerve-fibre derives 

 from the axis - cylinder only, without participation of the 

 medulla. These nerves, under favourable conditions, yield very 

 strong currents as also the mantle nerves of Eledone, in which 

 the E.M.F. amounts, according to S. Fuchs (4), to 0*0259 Dan., 

 though they are frequently of smaller diameter than the sciatic 

 nerves of large Transylvanian frogs. Gotch and Horsley (5) 

 find a striking difference of potential between longitudinal and 

 artificial transverse sections in the spinal roots of mammals. 

 While the E.M.F. of the demarcation current- of mixed mammalian 

 nerve is O'Ol Dan. in cat, 0'005 Dan. only in monkey, it amounts 

 in the posterior spinal roots of the cat to 0'025 Dan., and even 



