:;66 



NATURE 



{April 17, 1879 



ceeded, by employing better contrivances, in demonstrating with 

 the galvanometer the electrotonus of muscle. 



An important addition to our knowledge of the electrotonus 

 of nerves will be discussed at length in the sequel. 



IV. The Electrical Currents of Organs in Activity. — 

 A. Muscles 



The Fall in Potential accompanying the Excitatory Wave 



After Helmholtz had proved in the case of nerves, and Aeby 

 in the case of muscles, that excitation is transmitted along the 

 fibres with a measurable velocity, J. Bernstein undertook to 

 investigate the electrical processes associated with the transmis- 

 sion.^ To do so, he employed an instrument of his own 

 devising, by means of which he could discover the electrical 

 conditions of a muscle at any period after stimulation. He 

 found in muscle on direct stimulation that a zone or section of 

 negative potential arose which travelled down the fibre from the 

 stimulated point with the same velocity as the wave of contraction. 

 This phenomenon was readily explained by the theory of du 

 Bois-Reymond, according to which the molecules of excited 

 tissue suffer a diminution of activity, whence all excited spots 

 must be electrically negative in relation to the inactive parts of 

 the organ. Accordingly the phenomenon was designated 

 "undulatory propagation of the negative variation." 



On the assumption already made that excited tissue has, 

 like dying tissue, a lower potential than the unchanged tissue, 

 the fact is also at once explained, and I have named the cur- 

 rents called into being by the contact of excited with resting 

 tissue, "functional currents" (Actions strome).^ 



The Phasic and the Tetanic Functional Current 



When a single excitatory wave runs over a muscular fibre 

 which is connected at two points with the poles of a galvano- 

 meter, that point is of lower potential than the other beneath 

 which the excitatory wave is passing at the time ; or, if a wave 

 happens to be passing both points at once, that point has the 

 lower potential where the wave has the greater intensity or the 

 stronger phase. Hence arises what may be called a " phasic 

 functional current," the initial phase of which is a current pro- 

 ceeding from the stimulated spot, and the final phase a current 

 in the opposite direction. The two phases are equal when the 

 excitatory wave suffers no diminution in its course. 



If a muscular fibre is tetanised, whether excitation travel in 

 an undulatory form down the fibre or seize it as a whole, every 

 galvanometer-pole applied to the muscle will be of higher or 

 lower potential, according to the excitatory value of the points 

 of application. 



The Tetanic Functional Currents of Injured and Uninjured 

 Muscles. 



The first observations of du Bois-Reymond related to the 

 tetanic functional current of muscles with artificial cross-sections. 

 In such muscles the tetanic functional current is opposed to the 

 demarcation-current, and manifests its influence in a "negative 

 variation or deflection " of the latter. Since I regard the func- 

 tional current as due to living muscle approximating in a certain 

 degree to the condition of dying muscle, I have denominated 

 such functional currents as diminish a demarcation-current "level- 

 ling," or "equalising," currents (ausgleichende). 



Subsequently du Bois-Reymond discovered that uninjured 

 muscles also exhibit a tetanic functional current proceeding from 

 the stimulated point towards the end of the muscle. In order 

 to reconcile this with his theory it became necessary to assume 

 that the parelectronomic layer at the extremity of the fibre took 

 part either not at all, or but slightly, in excitation. Finally the 

 latter alternative was adopted, and it proved to be nearer the 

 truth ; for it was discovered that the functional current of unin- 

 jured muscles is less powerful than that of muscles cut across.^ 

 In a word, in order to explain the functional current of unin- 

 jured muscle, it was found necessary to assume that the ex- 

 tremities of a muscular fibre are less concerned in excitation 

 than the middle. 



While du Bois-Reymond was thus confining the limited par- 

 ticipation in excitation to the extremities of the fibre, or, in 

 other words, was locating the origin of the functional current in 



' J Bernstein, " Monatsber. d. Berliner Acad." 18671 p. 72; "Arch. f. d. 

 ges. Physiol." i. p. 173, 186S ; " Untersuchungen ii. den Erregungsvorgang, 

 &c.," Heidelberg, 1871. 



= " Untersuchugen," Heft iii. p. 61, 1868 ; " Arch. f. d. ges. Physiol." xvj. 

 p. 193, 1877. 



3 l>u Bois-Reymond, "Arch. f. Anat. u. Physiol.," 1873, p. 54S. 



the end of the fibre, it occurred to me that the excitatory wave 

 in its course over a muscular fibre might diminish in intensity ; ^ 

 whence it would follow, according to what was said in the fore- 

 going section, that in tetanus an electrode placed near the 

 stimulated point would have a lower potential or be electrically 

 negative, to an electrode more remote. The direction of the 

 diminutional or decremental current so obtained would agree 

 both with observed facts and du Bois-Reymond's theory ; but 

 its force, instead of residing in the end of the fibre, is equally 

 distributed over the whole course of the excitatory wave. 



The Diminution in Intensity of the Excitatory Wave in Excised 

 Muscles 



Shortly after I had expressed my belief that the excitatory 

 wave would be found to diminish in intensity in its passage 

 down the muscle, Bem.stein actually observed that it was so.* 

 But du Bois-Reymond surmised that the phenomenon might be 

 the result of the abnormal conditions of the experiment, and 

 ought, in fact, to be attributed to the moribund state of the 

 excised muscle ; and in support of his surmise he stated that 

 perfectly fresh muscle, on direct stimulation, exhibits no decre- 

 mental functional current between any two points of its sub- 

 stance.3 He persisted, therefore, in assigning the origin of the 

 functional current to the parelectronomic layer. Moreover, he 

 expressed a doubt whether, on stimulating a muscle through its 

 nerve, excitation is propagated along the muscle in the form of 

 undulations. 



Meanwhile, in my own experiments I invariably detected the 

 decrement of excitatory wave in excised muscles, a decrement, 

 it need hardly be observed, which increased with the degree of 

 exhaustion of the muscle.* Further, I hit upon the following 

 proof that the force of the functional currents is evenly dis- 

 tributed over the whole fibre. If, while a muscle is being 

 tetanised at one end, the points of application of the galvano- 

 meter electrodes be shifted in relation to one another and to the 

 seat of stimulation, a functional current will invariably be dis- 

 covered proceeding away from the stimulus ; and the force ol 

 the current will be found to depend solely upon the interval 

 between the galvanometer poles, irrespective of their position in 

 relation to the end of the muscle.^ The same observations may 

 be made on a muscle which is tetanised through its nerve.® A 

 functional current may always be abducted from the muscle, the 

 force of which is exclusively determined by the respective dis- 

 tances of the abducting electrodes from the " nervous equator " '' 

 of the muscle. 



'J he above experiments prove that excitation, even on nervous 

 stimulation, proceeds in the form .of a wave ; that in excised 

 muscles it always suffers a decrement ; that the tetanic functional 

 current is decremental in its nature ; and tiat its origin is not 

 restricted to the ends of the muscular fibres, but is distributed 

 over the whole course of the excitatory wave. 



The Phasic Functional Current developed on Stimulation 

 through Nerve 



The first examination of the phasic functional current of a 

 muscle which is excited through its nerve was made by S. Mayer, 

 under the supervision of Prof. Bernstein ; ^ in their researches 

 the gastrocnemii of frogs were used. They made out that stimu- 

 lation was followed by the development of two currents in suc- 

 cession, of which the first to appear was a descending current 

 and the second an ascending current. If the gastrocnemius had 

 been previously injured at its lower end, the second, or ascend- 

 ing, current was less pronounced. 



These results were subsequently established by some experi- 

 ments of du Bois-Reymond,^ as veil as by others which I made 

 with a special non-repeating apparatus adapted to single stimuli.^** 

 Du Bois-Reymond explained the phasic current as due to the 

 asynchronism of the two forces concurring to produce the 



' " Untersuchungen," Heft iii., p. 60, 1868. 



^ Bernstein, "Untersuchungen, &c.," p. 64, 1871. 



3 Du Bois-Reymond, "Arch. f. Anat. u. Physiol.," p. 369, 1876. 



4 "Arch. f. d. ges. Physiol.," xvi. p. 194, 1877. 



5 Jbid., p. 217. 6 Ibid., p. 229. 



^ Each constituent fibre of a muscle receives the mctorial end-organ of a 

 nerve-fibre. The motorial end organs of all the fibres are not absolutely in 

 the same plane; and by the term "nervous equator" I h.-ive designated 

 their w/fa« ^fz»<?/ in a given muscle. The " nervous equator " is that equa- 

 torial section of a muscle in relation to which the distances of the various 

 motorial plates, when algebraically summed, amount to nothing. See 

 "Arch. f. d. ges. Physiol.," xvi. pp. 234, 414, 1878. 



8 S. Mayer, "Arch. f. Anat u. Physiol.," 1S68, p. 655. 



9 Du Bois-Reymond, " Arch. f. Anat. u. Physiol.," 1873, p. 584. 

 '° " Arch. f. d. ges. Physiol.," xv. p. 235, 1877. 



