ELECTRICAL RELATIONS OF MUSCLE. 817 



ings taken with levers attached to different parts. In like manner, when 

 the nerve supplying a muscle is excited the whole muscle appears to con- 

 tract simultaneously, and this is explained by Aeby on the supposition that 

 the contraction commences at the point of entry of each terminal twig of the 

 nerve, and propagates itself away from this point in both directions. As 

 these points of entry are distributed very irregularly in neighboring fibres, 

 the swelling appears to be uniform throughout. In one of his experiments, 

 a muscle of a frog is taken, the motor nerve of which bifurcates as it enters. 

 One of the divisions is cut, and the main trunk excited. It is then found 

 that that portion of the muscle which is supplied by the intact nerve con- 

 tracts simultaneously throughout, whilst in the remaining portion a wave is 

 propagated that travels at precisely the same rate as the contraction that oc- 

 curs when mechanical irritation is applied to a given point of a fresh muscle. 

 The rapidity of this last is given by Aeby, 1 for the muscles of frogs at about 

 40 inches per second, Bernstein 2 estimated it far more highly at nearly 13 

 feet per second, and quite recently Hermann, 3 operating on the muscles of 

 frogs, both with and without woorara, gives the rapidity at 2.698 metres per 

 second, or about 9 feet. M. Marey 4 has lately shown by means of his deli- 



Fio. 293. 



cately constructed registering apparatus, that a contraction of a muscle 

 which follows the application of a sudden stimulus, as of an electric spark, 

 differs remarkably from the contraction induced by a voluntary impulse. 

 In the former instance the contraction is sudden and single, especially if 

 the muscle be quite fresh, becoming slower as the muscle experiences 

 fatigue. This is clearly shown in the preceding woodcut, which represents 

 the tracing obtained on a rapidly rotating circular disk from a muscle made 

 to contract by the opening and closing of a galvanic current. Two contrac- 

 tions, or, as M. Marey terms them, impulses or shocks (secousses) are ex- 

 hibited. One series (o) corresponding to the period of opening of the in- 

 duced current, the other of closing (o). The line traced at the bottom of 

 the figure by a diapason vibrating 100 times (double vibrations) per second 



1 Untersuchungen iiber die Fortpflanzungsgeschwindigkeit der Keizung, etc., 

 Braunschweig, 1862. See also v. Bezold, Meissner's Jahresbericht, 1860, p. 482; 

 Engelmann, Jenaische Zeits., Bd. iv, p. 305; Place, Onderzoek. ged. in bet Phys. 

 Lab. der Utrecht Hoogeschool, Bd. ii, Recks i, p. 135; Valentin, Pliiger's Archlv, 

 Bd. iv, p. 115. 



2 Untersuchungen, etc , Heidelberg, 1871, p. 76. 

 Pfliiger's Archiv, Bd. x, 1875, p.~54. 



4 See his Lectures on Self-registering Apparatus, in the Revue des Cours Scien- 

 tifiques, torn. iii. 



