5^4 



NATURE 



{April 17, 1879 



of independent cellular elements placed one behind the other in 

 rows, and the current of one section can therefore only last until 

 the injured cells have died from end to end. ^ In the last place 

 the same phenomenon was discovered, in the case of nerves, by 

 Engelmann. Here the nodes of Ranvier constitute cellular 

 boundaries which effectually confine the process of death ^ to the 

 internode immediately injured during section, although they 

 offer no greater barrier to the transmission of the excitatory con- 

 dition than do the cell-boundaries in the heart, intestines, or 

 uterus. ^ 



Disappearance of Demarcation Currents {Demarcations-stronte) 

 under the Influence of the N'attiral Reparative Processes of the 

 Body 



It was reserved for Engelmann to discover yet another fact 

 opposed to the doctrine of the pre-existence of electrical forces 

 in muscle.* If in a living frog a muscle be divided subcu- 

 taneously the negative potential of the artificial section dimi- 

 nishes continually, and ultimately disappears, under the influence 

 of the blood circulating in the part and of the nerves supplying 

 it. As, therefore, nature tends to render artificial sections 

 currentless, it is clear that in the natural condition no muscle 

 can be the seat of currents, but every muscular current observed 

 during rest must spring from injuries. 



Inasmuch as all currents exhibited by muscles and nerves 

 in a condition of inactivity (except those caused by inequalities 

 of temperature or by the passage of extraneous currents) depend 

 apon the contact of dying and living matter, and since the electro- 

 motive force has its origin in the surfaces which form the 

 boundary between the two, I have called these currents of rest 

 *' demarcation currents" (Demarcations-strome). 



Influence of Temperature 



If the muscular substance within the same fibre exhibits differ- 

 «nces of temperature the warmer spots possess^ a higher potential 

 than the colder, so long as the [temperature does not attain the 

 limits of heat-rigor, and the consequent negative potential ensue. 

 In exactly the same degree as living substance acquires through 

 heat a higher potential than other living substance, is its potential 

 exalted as regards dying substance. Hence, it is not merely that 

 the demarcation-current becomes more powerful by heating the 

 whole muscle, as was in part revealed to du Bois-Reymond, and 

 recently established by Steiner in regard to nerves, but the force 

 of the demarcation-current is dependent only on the tempe- 

 rature of the living substance at the point of application of 

 one galvanometer- electrode, and not on the temperature of the 

 substance lying between the poles. In a word, portions of 

 muscular substance in different conditions form together a voltaic 

 series.^ 



The Currents of Entire Muscles 



As has been already remarked, wholly uninjured muscular 

 fibres possess no current. All currents of muscles at rest are, 

 therefore, variations in temperature excepted, the results of 

 injuries. The properties of the current are most simple in the 

 case of a muscle with parallel fibres, and cut transversely at right 



Fig. 2. 



angles. In this case all the boundary surfaces between dying and 

 living tissue are parallel to the section, and every point in the 

 transverse surface has a lower potential than any point in the 



* I made an exactly similar observation In the spring of 1877 on the 

 tissues of young Medusae which were sent to me through the kindness of 

 Prof. Hensen, of Kiel. 



2 Engelmann, " Arch. f. d. ges. Physiol, xiii., p. 474, 1876. 



3 Gad und Tschiriew (" Verhandl. d. physiol. Ges. zu Berlin," 1877, Nr. 

 2t) deduce the disappearance of the current in nerves from the fact that, 

 after the death of the divided intemodes the seat of electromotive force, viz., 

 the ends of the interncdes of the next row are na longer in one trans- 

 verse plane, whence the resulting current is much diminished by partial 

 equalisations. The value of this observation is obvious when it is remem- 

 bered that the length of the intemodes of Ranvier is, generally speaking, only 

 I — I J mm. 



4 Engelmann, " Arch. f. d. ges. Physiol.," xv., p. 328, 1877. 



5 " Arch. f. d. ges. Physiol ," iv. p. 163, 1S71. 6 Ibid., p. 178. 



longitudinal surface.^ As, however, the muscle possesses 

 between its fibres and on its surface indifferent conducting 

 tissues through which the demarcation-currents can in great part 

 become equalised — such ti-s^sues as sarcolemma, perimysium, 

 the dead tissue of the cross-section — two important results 

 follow. In the first place the force of the currents obtained by 

 applying the galvanometer poles to two spots of different poten- 

 tial represents but a fraction of the electromotive force of a 

 single fibre. In the second place the positive potential of the 

 longitudinal surface and the negative potential of the transverse 

 surface are so distributed as to be most marked at the centre of 

 the respective surfaces. Hence ari.se the so-called "weak 

 currents" when the galvanometer poles are applied to un- 

 symmetrical points on the transverse or longitudinal surface." 

 But the weak currents of longitudinal surfaces may, especially in 

 nerves, be in part due to an electrotonic extension of the demar- 

 cation-current which will be the subject of discussion later on. 



In oblique sections there occurs a peculiar arrangement of 

 the level-lines ^ (Niveau-linien), inasmuch as there intervenes an 

 electromotive force which is directed from the acute to the 

 obtuse edge of the slanting section : such currents are called 

 "currents of inclination." Du Bois-Reymond explains this 

 force by the step-like arrangement which the terminal molecules 

 form in the slanting section ; but it is clear that the same mode 

 of explanation is just as well adapted to the step-like arrange 

 ment of the boundary-surfaces between dying and living tissue 

 in the successive sets of fibres (Fig. 3). 



Fig. 3. 



The molecular theory, therefore, is not needed to explain the 

 currents of inclination of a bundle of fibres ; it would only be 

 indispensable in the case of a current of inclination of a single 

 obliquely-cut fibre, did such a fibre possess one ; but this is 

 precisely what no one has demonstrated or can demonstrate. The 

 circumstance that many muscular fibres present slanting facettes 

 at their terminations in tendons * offers no opportunity to support 

 the molecular theory ; for such tendons possess no current of 

 inclination in the uninjured condition, while, in the injured con- 

 dition, the tissue of each fibre invariably dies down to a surface at 

 right angles to the long axis of the fibre, and thus the conditions 

 for the current of inclination arise (Fig. 3). 



In all cases of partial injuries to muscle it is only the injured 

 fibres which are the seat of electromotive action ; the remainder 

 merely form indifferent conductors which give facilities for 

 local equilibrations. The weak currents of such muscles have, 

 therefore, no regular relation to the surface of the muscle, as all 

 depends upon the situation of the injuries : hence the irregular 

 currents of so-called parelectronomic muscles. 



When injuries, of whatever kind, affect the whole surface of a 

 muscle, the probability is that a current will be detected in the 

 muscle flowing from one end of it towards the longitudinal sur- 

 face; and, in fact, when tested, this is found to be almost 

 always the case. If a slight injury has been inflicted upon the 

 lateral surface of a muscle the death- changes in fibres which 

 have been opened longitudinally will speedily be checked at the 

 boundary of the next fibre, while the death-changes which have 

 been started at the ends or cross-sections will creep along the 

 whole length of the fibres and occasion a lasting current. This 

 has been previously alluded to, when the transitional nature 

 of the demarcation-current in the heart, intestines, &c., was 

 explained. 



Local injuries to the external surface of a muscle give rise to 

 local currents ; but these currents, when a conductor is stretched 

 from the longitudinal to the transverse surface, produce hardly 

 any effect ; whilst the demarcation-currents at the dying end of the 

 muscle are under very favourable conditions for conduction, and 



' The best methad of applying the electrode to an artificial transverse 

 section of muscle ; so as to avoid any abduction 'of current from the "v.ng 

 portion, is to produce a heat-rigor of the end of the muscle.^and to apply the 

 electrode to the rigid part ("thermal cross-section ") ; cf. Arch. t. d. ges. 

 Physiol.," iv. p. 167, 1871. 



^ Du Bois-Reymond, " Untersuchungen," i. 1848. . 



3 Du Bois-Reymond, "Arch. f. Anat. u. Physiol., 1863, p. 32 1! 

 "Monatsber. d. Berliner Acad.," 1866, p. 387. , ,, o 



4 Du Bjis-Reymond, " Monatsber. d. Berhner Acad., 1872, p. 791. 



