April 17, 1879] 



NATURE 



565 



the forces of the local currents are, on account of the usual 

 oblique application of the mu.=cular fibres to their tendons, 

 generally summed into currents of inclination. 



II I. — Electrotonus 



Considerations opposed to the Molecular Theory of Electronus 



The explanation adduced in the Introductory Remarks, in order 

 to elucidate the electrotonic condition of nerves has many theo- 

 retical difficulties which cannot be here entered upon. The theory 

 appears, however, to be amenable to an experimental proof. If, 

 namely, the molecules of the portion of a ners-e traversed by a 

 current arrange themselves in the direction of the current, the elec- 

 tromotive force of the current should receive a very appreciable 

 increase ; or, in other words, the current should become very 

 much greater when it passes through a piece of living nerve 

 than when it traverses a dead piece of similar dimensions. On 

 trjing this experiment, however, I find no such difference ; or 

 the differences found are far from agreeing with the molecular 

 theory.^ 



Electrotonic Phenomena observed in Conductors with Polarisable 

 Cores 



An experiment of Matteucci's - gave the clue to an explana- 

 tion of electrotonic phenomena. He foimd that a metallic wire 

 which is surrounded by a moist envelope exhibits currents pos- 

 sessing the characters of the electrotonic currents of nerves, 

 whenever a galvanic current is passed, at any point, through 

 the moi.-t envelope. Matteucci discovered, in addition, that the 

 currents cease when the wire is of amalgamated zinc and the 

 envelope is moistened by a saturated solution of zinc sulfJiate. 

 Hence it follows that the phenomenon depends upon a polarisa- 

 tion between the core and the fluid. 



I examined the phenomenon more closely,' parsing metallic 

 wires through a glass tube filled with fluid and possessing lateral 

 processes fc r the conduction of currents, and my experiments 

 confirm the fact that electrotonic currents only occur when a 

 polarisable core is present. Further, it was seen that the cur- 

 rents only extended so far as both core and envelope possessed 

 unbroken continuity, whereas continuous contact of the two was 

 not necessary. Lastly, I determined the laws regulating the 

 tiaie of development of these currents, their duration, their ces- 

 sation on opening, their dependence upon the distance, and the 

 length of the portion of core traversed by the polarising current, 

 their combination and superposition, &c. All the phenomena 

 may be grouped wnthout difficulty under a simple theory. 



As the current a E -^ (Fig. 4) applied to the envelope endeavours 

 to reach the core k k, it splits up, if no polarisation be present. 



Fig. 4. 



in such a manner that only the conducting threads in the imme- 

 diate neighbourhood of the electrodes are able to catch an appre- 

 ciable branch of the current. If on the other hand polarisation 

 occurs at the surface of the core, this surface opposes a consider- 

 able and evenly distributed resistance ; and, as in relation to it, 

 the resistance offered by the length of the conducting wires is 

 small, the current, under the influence of polarisation, extends 

 much further along the conductor than when no polarisation 

 takes place. If a galvanometer circuit is arranged as shown in 

 the diagram (at G, G', or g") it receives an offset from the main 

 current as if there existed in the region examined an electro- 

 motive force of like direction with that of the polarising current. 



» " Untersuchungen," Heft iii. p. 67, i868 ; "Arch. f. d. ges. Physiol.," 

 VI. p. 328, 1872. 



* Matteucd, Comptes Rendns, Ivi. p. 760, 1863; Ixv. pp. isi, 104. 884. 

 1867; Ixvi. p. 580, 1868. " 



3 "Arch. f. d. ges. PhysioL," v. p. 264, 1871; \-i. p. 312, 1S72; \-u. p. 302, 

 1873. 



This polarisational extension of the current only continues where 

 both core and sheath are uninterrupted. 



The abducted currents are at the same time, on mathematical 

 grounds, a measure of the degree of polarisation at the points 

 touched ; and thus afford a means of tracing the extent of 

 polarisation along the core. The curve representing the polarisa- 

 tional values at various points of the core — in general an ex- 

 ponential cun'e — has at the positive pole a positive maximum 

 and a negative at the negative pole. In the region traversed by 



Fig. 5. 



the current the curve cuts the axis at the so-called "indifferent 

 point" (Fig. 5, i) ; and in the extra-polar regions it approaches 

 the axes on both sides asymptotically. The curve is represented 

 in Fig. 5, where, as a matter of subsequent convenience, the 

 ordinates of positive polarisation are taken below the axis instead 

 of above. 



Interned Transverse Polarisation of Muscles and Nerves 



In the year 1871 I discovered that the resistance offered by 

 muscles and nerves to the passage of a current across their fibres 

 was from five to nine times greater than the resistance offered by 

 a current passing in direction of the fibres.^ In the case of 

 muscle this difference disappears almost entirely when rigor seta 

 in ; whilst in dead ner\-es it certainly persists, though reduced to 

 one half. Further investigation of these facts disclosed their 

 dependence upon a specific internal polarisability, which, in the 

 case of muscle, is entirely associated with the living condition, 

 and, in the case of nerve, in great part so associated. This fitness 

 for polarisation by transversely-directed currents can only be 

 due to a stratification of heterogeneous conductors across the 

 tissue, which is wanting in its longitudinal axis. And since it 

 is common to muscles and nerves, the stratification on which it 

 depends must be sought in the typical stnicture which is common 

 to the two organs, ^^z., the tubular nature of the fibres. We 

 may assume, therefore, that polarisation takes place between 

 the peculiar, active, substance of muscle- and ner\'e-fibres and 

 the indifferent tissue ensheathing it. 



Explanation of the Electrotonus of Nerves 



As, accordingly, there exist in nerve-fibres all the essentia! 

 conditions of the electrotonic extension of currents in conductors 

 with polarisable nuclei, it may be assumed that the electrotonus 

 of ner\'es is fully explained.- It is true that the core-substance 

 of nerves is no better a conductor of electricity than the sheath- 

 substance, while in the sheathed wire of Matteucci's experiment 

 the core was of metal. But theory teaches that the electrotonic 

 extension occurs even when the conducting powers of sheath 

 and core are equal, if only polarisation takes place between the 

 two. 



This explanation of electrotonus, as I have shown in detail, 

 completely covers all the phenomena. Especially does it 

 accoimt for the facts that the electrotonic state requires no appre- 

 ciable time for its establishing ; ' and that it cannot extend past 

 a ligatured spot. Whenever a ner%'e is crushed, the continuity 

 of the core is broken, since, at the crushed spot, the core is 

 killed and converted into indifferent tissue. 



As muscle-fibres also possess polarisable cores, they must be 

 endowed with electrotonic properties ; nevertheless, neither 

 du Bois-Reymond nor I at first succeeded in demonstrating 

 them by galvanometric means ; though, truly, just as little 

 could their absence be distinctly affirmed. But theoretical con- 

 siderations disclosed the reasons why muscle was less favourable 

 to electrotonic phenomena than nerve ; * and lately I have suc- 



' " Arch. f. d. ges. Physiol.," v., p. 223, 1871. 

 ^,Ibid., \\. p. 328, 1872. 



3 " Helmholtz, "MoDatsber. d. Berliner Acad.," p. 328, 1S34 ; L. Her- 

 mann, " Arch. f. d. ges. Physiol.," viii. p. 272, 1874. 

 * " Arch. f. d. ges. Physiol.," vi p. 350, 1872. 



