Aprtl 17, 1879]! 



NATURE 



567 



functional current. These forces were assumed to be locatetl in 

 the two extremities of the muscular fibres and to be directed 

 each to the correspondent end of the fibre, on which account they 

 v.ould of necessity overlap. The descending functional cturent 

 belonging to the lower end was supposed to arise more quickly 

 and' to disappear earlier than the ascending current of the upper 

 end ; and hence the appearance of phases. Inasmuch as injury 

 to one of the ends of a muscle (or in other word?, removal of 

 the parelectronomic layer), according to Du Bois-Reymond, 

 intensifies the functional current proper to that end, it is clear 

 that, when the inferior extremity is injured, the lower (descend- 

 ing) functional current obscures the upper. ^ 



My own explanation * is essentially different from du Bois- 

 Rejrmond's. According to my views tiie muscle must exhibit a de- 

 scending current when the excitatory wave is at the upper end of 

 the muscle, and an ascending current when at the lower end. 

 Hence it is not the first, but the second phase, which is proper 

 to the lower end of the muscle. The former, as I have shown, 

 pertains to the moment when the excitatory wave is in the 

 neighbourhood of the upper electrode — a condition most ad\-an- 

 tageously secured, owing to the peculiar structiu-e of the gastro- 

 cnemius, by placing the electrode so as to abduct a current from 

 the mid point of the fibres rather than from their upper end. 



According to this theory it is clear that the descending phase 

 must precede the ascending : for every excitatory wave b started 

 at the middle point of the muscular fibre where the ner>-e enters, 

 and only reaches the ends of the fibres at a later period. If, 

 however, the lower end of the fibre have suffered injury, the ex- 

 citatory wave running towards the injured part will be powerless 

 to cause a current, owing to the constant negative potential of 

 the injured end, and hence the second, ascending pha!se comes to 

 nothing. 



The fitness of this explanation was placed beyond doubt by 

 experiments on the phasic fanctional current of regularly-con- 

 structed muscles.^ In such mnscles^there invariably appeared 

 in each half first an atterminal and then an abterminal phase 



"V" 



"F" 



Fig. 6. 



(Fig. 6). The atterminal phases in both halves (I in Fig. 6) 

 coincide in time, arising, as they both do, in the mid-point of 

 the fibre at the starting of the excitatory wave ; in other words, 

 the middle point of the fibre becomes negative in comparison 

 with either end. 



In like manner the abterminal phases of b^th halves coincide 

 (2 in Fig. 6), being produced by the arrival of the excitatory 

 waves at the extremities of the fibre : in other words, either end 

 of the fibre becomes negative in comparison with the mid-point. 



In this manner the wave-like propagation of the excitatory 

 condition in muscle was established for the case of muscle 

 stimulated through ners'es, and, at the same time, another proof 

 was afforded that the force of the functional current does not 

 exclusively reside in the ends of the fibres. 



Furthermore, it was directly shown in these experiments that 

 the excitatory-wave in excised muscles, while traversing the 

 fibres, experience^ 1 liiminution; for the second, abterminal 

 phase was invariaL;-.- much weaker than the atterminal, as is 

 indicated in Fig. 6 by the length of the arrows and the height 

 of the representative cur\'e, and it invariably further diminished 

 in the course of an experiment. 



The Functional X^urrent in wholly Uninjured Muscle in Man 

 In the case of man the currents of normal resting muscle 

 were secured ft-oni investigation by the obstacle of the' skin. 

 But Du Bois-Reymond found, during the violent voluntary con- 

 traction of the muscles of an arm or a leg, that the limb ex- 



hibited an ascending current. This he took to be the algebra- 

 ical sum of the tetanic functional currents of all the muscles 

 exerted, although such an explanation only became very probable 

 by the exclusion of certain other experiments designed to eluci- 

 date the matter.^ But the current could never be demonstrated 

 under the most favourable conditions of abduction, viz., by the 

 application of the galvanometer wires to indiNadual groups of 

 muscles,* 



The question whether the diminution of the excitatory wave 

 only occurs in excised muscles as a result of death changes, 

 could, of course, only be settled by experiments on living 

 human beings. And since the manifold disturbances inseparable 

 from the method of experiment rendered the tetanic functional 

 current almost useless for this investigation, I undertook to 

 examine the phasic current in the muscles of the fore-arm.' I 

 found that the same relationship held for the muscles of man a. 

 had before been shown to exist in the case of the frog. The 

 first phase is an atterminal current in which the region of the 

 nerv'ous equator — about 10 cm. below the elbow — becomes nega- 

 tive in comparison with the two ends ; the second phase is 

 abterminal, i.e., the ends of the muscles become negative in 

 comparison with the equator (Fig. 7). But in the perfectly 



* Du Bois-Reymond, loc. cit., 1873-76. 



• " Arch. f. d. ges. PhysioL," rvL p. 236. 



3 Ibid., p. 239. 



Fig. 7. 



normal muscles of man the second phase was not weaka* than 

 the first — a relation which was constant in the excised muscles of 

 the frog. And hence we may conclude that in absolutely normal 

 muscles the excitatory wave does not diminish in intensity. 

 These experiments, which constitute the first regular examination 

 of muscular action in living man, further taught approximately 

 the rate of propagation of the excitatory wave in human muscles, 

 viz., from 10 to 13 metres yer second. 



The Absence of the Functional Current when none of the above 

 Conditions of Electrical Inequality exist in Muscle 



If an uninjured, currentless muscle be thrown into the active 

 condition by a stimulus affecting its whole mass at once, it never 

 exhibits any functional current,* whether the stimulus be single 

 or tetanic. The explanation of this is ob\-ious. In such a 

 totally excited muscle the whole substance passes at the same 

 moment into the same degree of excitation ; and, hence, is 

 nowhere the opportunity given for the contact of excited with 

 non-excited or imperfectly excited tissue. 



If, on the other hand, the muscle possesses an artificial trans- 

 verse section with the associated boundary current, then indeed 

 a levelling or equalising functional current arises on total exci- 

 tation and diminishes the ourent of injury.' 



When muscles are tetanised through their nerves, fimctional 

 currents only appear where the excitatory wave has not the same 

 intensity throughout the tetanised mass. Hence in man, whose 

 muscles when under absolutely normal conditions exhibit no 

 diminution or decrement of wave, it is impossible to demonstrate 

 a tetanic functional current. I have, indeed, when using very 

 powerful and fatiguing stimulation, now and then succeeded in 

 getting indications of such a decremental functional current, but 

 from some cause or other, we cannot depend upon this experi- 

 ment to lead to a constant result, perhaps for the reason that the 

 conductivity of human muscles is but slightly hampered by fatigfue, 

 or possibly because the collateral effects of stimulation mar the 

 experiment.® I may be allowed to remark here that certain 

 experiments now in course of publication show very clearly that 

 stimulation of human muscles causes a secretory cutaneous 

 current directed from without inwards. This current is the true 



' Du Bois-Reymond, " Untersuchuugen," iL, Abth. 2, p. 267. 

 ' "Arch. f. d. ges. Physiol.," xvi., p. 257, 1S77. 



3 Ibid., xvi., p. 410, 1873. 



4 " Arch. f. d. ges. Physiol.," xvi., p. 203, 1877. . , 



5 Ibid., XV., p. 238; xvi., p. 203, et seq., 1S77. 



6 Ibid., ztL, p. 416, 1878. 



