568 



NATURE 



{April 17, 1879 



cause of the negative potential exhibited by the voluntarily con- 

 tracted muscles of one limb when compared with the opposite 

 but unexerted limb, and is therefore the ciurent which du Bois- 

 Raymond took for the muscular functional current of man,^ 



B. — Nerves 



T/ie Functional Current of Nerves retnotefroin all Tratisverse 

 Sections 



In the nerves of the frog, according to Helmholtz, excitatory 

 waves are propagated at the rate of twenty-eight metres per second. 

 Hence, if the two ends of a galvanometer circuit were laid upon two 

 points of a nerve a functional current should be manifest on stimu- 

 lation of the nerve, and should consist of two phases according as 

 the excitatory wave was passing one or the other of the electrodes. 

 Nevertheless the functional cinrent of nerves, owing doubtless 

 to its exceedingly fleeting character, has hitherto escaped detec- 

 tion.' Since the excitatory wave of nerves does not diminish in its 

 course, it is to be expected that the two phases of the nervous 

 functional current will be equal ; and hence also it is that in 

 tetanic stimulation, where we have to do with the algebraical 

 sum of these two equal and opposite phases, we obtain no func- 

 tional current whatever in uninjured nerves. 



The Functional Current of Netves at a Transverse Section 

 The functional current of nerves bounded by an artificial trans- 

 verse section was discovered by du Bois-Reymond; itisanequal- 

 isingcurrent, and consists, therefore, in adiminution of theconstant 

 demarcation current. Du Bois-Reymond onlyfound this current in 

 nerves tetanically stimulated, but Bernstein, by means of his appa- ' 

 ratus already referred to, succeeded in demonstrating its presence 

 in the case of single excitatory waves. ^ If the poles of the galva- 

 nometer circuit are applied, one to the artificial cross- section, 

 and the other to a point in the longitudinal surface, the diminu- 

 tion of the demarcation current occurs in the instant that the 

 excitatory wave passes the latter, or longitudinal pole. By 

 altering the position of this pole, the progress and the course in 

 time of the excitatory wave may be examined. The rate of 

 progression so deduced was found to agree with that determined 

 in other experiments by varying the distance between the point 

 of the nerve at which a stimulus was applied and the fixed 

 point at which the result of stimulation was manifested, 

 viz., the dependent muscle, or the pole applied to an artificial 

 cross-section. And this similarity of re.-ult established the 

 identity of the process occurring during excitation, and the wave 

 of negative deflection.* The way in which the wave comports 

 itself on approaching the artificial cross-section will be explained 

 below. 



The Functional Current oj Polarised Nerves : the Polarisational 

 Increment of Excitation 



In 1 866 Bernstein found ^ that the electrotonic currents of 

 nerve, on stimulation of the nerve, suffer diminution like the 

 demarcation-currents. As a disciple of the molecular theory he 

 explained this phenomenon in the following way : Since the 

 electrotonic currents depend upon an altei-ed arrangement of the 

 molecules, and since the force of each molecule diminishes on 

 stimulation of the nerve, therefore the electrotonic currents 

 must also be lessened during excitation. And so the new phe- 

 nomenon seemed to be completely covered by the molecular 

 theory. In my view, however, the electrotonic currents are 

 merely offsets diverted from the main polarising current owing 

 to the internal polarisation of the nerve itself. Since these 

 offsets could not be supposed to be modified during excitation, I 

 concluded that every apparent diminution depended upon a 

 functional current which arises owing to the polarised condition 

 of the nerve, and which is opposite to the polarising current in 

 direction. I assumed, as the cause of this functional current, 

 that the excitatory wave failed of maintaining its magnitude 

 while passing through the polarised portions of nerve ; it in- 

 creased as it reached more positively or less negatively polarised 

 areas, and diminished under the opposite conditions. This is 

 called the doctrine of the "polarisational increment of excita- 



' These experiments have been recently published ; cf. Hermann and 

 Zuchsinger, " Arch. f. d. ges. Physiol.," xvii. p. 310, 1878. 



* I have succeeded in detecting these currents by extending the rate of 

 propagation in the nerve by cold ; and by using a bundle of four or six nerves 

 together. Cf. " Arch. f. d. ges. Physiol," xviii., p. 574, 1878. 



^ J. Bernstein, loc. cit. 



< The new experiments referred to in the last note confirm this indirect 

 conclusion in a more direct manner. 



5 J. Bernstein, "Arch. f. Anat. u. Physiol." p. 596, 1S66. 



tion,"^ and it is clearly competent to explain Bernstein's 

 observations. 



If this assumption be reasonable, the excitatory condition 

 travelling along the nerve should be most intense at the anode 

 of the polarising current, and least intense at the cathode ; and 

 hence there should be present in the intrapolar region a 

 powerful functional current of like-direction with the polarising 

 current and reinforcing it. Such an intrapolar current I did, in 

 fact, discover to be constantly present ; ^ though afterwards it 

 appeared that a similar observation had previouisly been made by 

 Griinhagen, by whom, however, the current was otherwise ex- 

 plained as the effect of a diminished resistance in the nerve 

 during excitation, leading to an increase in the polarising 

 current.3 Before I had any knowledge of this early observation 

 of Griinhagen, the probability of the explanation which he 

 assigned to it had been tested by me, and numerous indications 

 had been found that the intrapolar increase of current was 

 indeed an electromotive phenomenon and not due to a diminished 

 resistance.* But later I was enabled to settle the question in 

 the most direct manner, by the discovery that the transverse 

 rpsistance of nerves is not diminished during excitation — excita- 

 tion having in general no manner of influence upon the resistance 

 offered by the nerve.* 



Further Physiological Support of the Doctrine of Polarisational 

 Incranent 



In order to grasp the doctrine of polarisational increment, let 

 us regard the axis ti n' in Fig. 5 as representing a nerve, the 

 conditions of polarisation of which are indicated by the vertical 

 ordinates, positive polarisation being exceptionally represented 

 by descending lines, and negative by ascending lines. With these 

 ordinates we can trace out the polarisation curve, nKiAn' 

 (already spoken of in describing Fig. 5, which see), the lowest 

 point of which corresponds to the anode, and the highest to 

 the cathode. Let us now suppose a ball, e, devoid of fric- 

 tion, and travelling through space A^ith a certain horizontal 

 initial velocity, to be set rolling along this curve. The vis 

 viva of the ball will then represent the magnitude of excita- 

 tion. It is at once evident that the initial velocity is increased 

 in the part of the curve below the line nn, i.e., in the 

 anelectrotonic region, but is diminished in the upper portions 

 of the curve, i.e., in the catelectrotonic region. If the initial 

 velocity is too small, the ball will not be able to reach the 

 summit of the catelectrotonic portion of the curve, or, in other 

 words, the excitation becomes dissipated in the corresponding 

 region of nerve, and never succeeds in passing the cathode. 

 Moreover, if the ball, with a certain initial velocity, were to be 

 set going at some point of the inferior (anelectrotonic) portion 

 of the curve, it would reach the outlying parts beyond the 

 polarised region with a diminished velocity ; while, if it were 

 set going upon a part of the curve (catelectrotonic) superior to 

 the line n n', it would reach the outlying parts with an increased 

 velocity. 



All these deductions from the doctrine under discussion have 

 been verified, in part by already established facts and in part 

 by recent observations. The experiments by Eckhard and 

 Pfliiger have shown that a certain stimulus applied to a nerve 

 produces a greater effect in the catelectrotonic region than in 

 the anelectrotonic. And it is cleai- that these phenomena are as 

 intelligible under my theory as under the as.sumption usually 

 made to explain them, viz., that the irritability of the nerve itself 

 is diminished during anelectrotonus and increased during cate- 

 lectrotonus.^ 



Moreover, certain facts are known which seem to imply 

 that, with a sufficient degree of polarisation, or with a suffi- 

 ciently slight stimulus, the excitatory wave becomes blocked 

 at the cathode.'' If to this we add that excitation does 

 not indefinitely increase with the stimulus, but soon reaches a 

 maximum, we may further conclude that, under certain condi- 

 tions, a diminution of excitation must take place even during the 

 passage of the wave through the anodic area.^ 



In the last place it is to be noticed, that the artificial section 

 of a nerve induces a negative polarisation or catelectrotonus of 



' "Arch. f. d. ges. Physiol.," vi., p. 359, 1872; vii., p. 323, 1873. 

 ^ Ibid., vi., p. 560, 1872; vii., p. 355, 1873; x., p. 215, 1875. 



3 Grunhagen, " Zeitsch. f. rat. Med." (3), xx.wi., p 132, 1869. 



4 "Arch. f. d. ges. Physiol.," x., p. 215, 1875. 



5 Ibid., xii., p. 151, 1875. 



6 Ibid., vii., pp. 325, 497, 1873. 



7 Ibid., vii., p. 354, 1873; ^'1 P- 226, 1875. 

 2 Ibid., vii., p. 361, 1873. 



