ACTION OF VOLTAIC CURRENT ON MUSCLE. 



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Fig. 245. — After Biedermann. 



Comparing these time-intervals with the corresponding distances of the 

 cathodes, we have a rate of propagation of from 1 to 2 metres per second. The 

 double myograph can also be used for comparing the character of the two con- 

 tractions, both myograms being recorded for this purpose on a slowly moving 

 surface. They show (Fig. 246) that the closure of a descending current evokes 

 twitches of about equal vigour in 

 both halves of the muscle, but in the 

 tibial (cathodic) half, the contraction 

 is prolonged until the current is 

 broken, the reason being that, whereas 

 the twitch is rapidly propagated from 

 the tibial to the pelvic end as a wave 

 of contraction, a prolonged contraction 

 occurs in the tibial half which shows 

 but slight, if any, tendency to spread. 

 For the same reason, when the direc- 

 tion of the current is reversed, both halves twitch, but the pelvic end, which 

 before relaxed instantly to its natural length, is now cathodic and behaves 

 accordingly. 



If the muscle is injured at one end (by dipping it into hot salt solution), 

 these phenomena are considerably modified. If the cathode is placed on 

 the devitalised 

 part, there is 

 scarcely any re- 

 sponse on clos- 

 ing; 1 both halves 

 twitch slightly. 

 If the injured 

 end is anodic, 

 the responses on 

 closure are the 

 same as they 

 would have been 

 had there been 

 no injury. 



One of the 

 facts stated 

 above as to the 

 polar effects of 

 the voltaic cur- 

 rent may be 

 confirmed by 

 direct inspec- 

 tion with the 

 aid of a lens of 



the surface through which the current enters or escapes. It can thus be 

 seen that if a current is led from end to end of a muscle, the cathodic end 

 swells during its passage. Other details may be made out by a method 

 devised by Biedermann — that of streaking the surface with a paste of 

 sepia, rubbed up with 0"6 per cent, salt solution. If the streaks cross 

 the fibres and are equidistant, it is easy to see that at the cathode the 

 streaks are drawn together from each side, and that this effect is a 



1 This fact was discovered at the same time (1880) by Engelmann and Biedermann. 

 See Engelmann, Arch. f. d. ges. Physiol., Bonn, Bd. xxvi. S. 97 ; and Biedermann, 

 Sitzungsb. d. k. Akad. d. Wissensch., Wien. Bd. lxxx. Abth. 3, S. 367. 

 VOL. II. 28 



Fig. 246. — Contractions of the two ends of the sartorius, as recorded by 

 the double myograph, v is the record of the tibial half, of the 

 pelvic half of the muscle. Note that the descending arrows 

 indicate an ascending current. The numbers indicate that the 

 strength of the current was the same throughout. — After 

 Biedermann. 



