432 



THE PROPERTIES OF STRIPED MUSCLE. 



The 'prolonged contraction. — The important distinction between the 

 persistent contraction which is scarcely, if at all, propagated, and 

 the twitch or wave of contraction, was further illustrated by Engelmann, 1 

 by a method of preparing the sartorius which has since proved to be of 

 great value in experimental work. The middle of the muscle is grasped 

 by a holder tight enough to prevent it from slipping when the 

 tibial end is made to lift a very light writing lever attached to the 

 tendon, but not tight enough to interfere with the propagation of 

 excitation. The battery electrodes are placed on opposite sides of the 

 holder, and the current is closed first from, then towards the tendon. 

 In the former case the curve has the character of the single twitch, in 

 the latter there is in addition a prolonged contraction. 



The specific character of the prolonged contraction, i.e. its claim to 

 be regarded as a phenomenon by itself, and not merely as an after-effect 

 or sequel to the primary response or twitch, is indicated, not only by its 

 persistence and the fact that its tendency to spread is inappreciable, 

 but also by the analogy of the conditions under which it manifests 

 itself with those which favour the production of Schiff' s " idiomuscular 

 contraction." The resemblance is sufficient to justify the surmise that 

 they are closely related phenomena. 



Some of the experimental facts by which earlier observers proved the 

 localisation of the make-excitations can be very satisfactorily demonstrated 



with the aid of Her- 

 ing's double myo- 

 graph, the construc- 

 tion of which will be 

 readily understood 

 from the figure (Fig. 

 244). If it is desired 

 to confirm v. Bezold's 

 experiment, the use 

 of this instrument 

 is combined with a 

 method of measuring 

 the period of latency, 

 in which the same 

 act that closes the 

 current sets a tuning 

 fork in vibration. 



Fig. 244.— Hering's double myograph. The sartorius muscle is "*■ -^ 1 S- **<>i •* 1S 



held in the middle between two pads of oil-clay (underneath seen that these vibra- 



q), so that each half can be extended horizontally independ- tions are inscribed 



ently of the other. Non-polarisable electrodes e e are applied Qn a rapidly niovin" 



to the bony attachments of the muscle. These are supported ,. p t 



on the vulcanite rod q in such a way that they follow the recording surface be- 



movements of the ends of the muscle, so that when it is tween the two myo- 



excited through them it can contract freely. Each end is grams, the upper of 



attached to a weight by a thread which passes over the wn i cn j s that of the 



pulleys R, r. RR are provided with pointers z z, which ... , , \. , , 



record their movements.— After Hering. tl „ Dl 7 nal *> ™ e , l0 ™ e \ 



of the pelvic halt of 



the sartorius. In the instance given, the current was descending, i.e. directed 

 towards the tibial tendon ; the contraction of the tibial (cathodic) half began 

 0-034 second after excitation, that of the pelvic (anodic) half 0'045 second. 



1 Engelmann, " Beitr. z. allg. Muskel- und Nerven-physiologie," Arch. f. d. gcs. Physiol., 

 Bonn, Bd. iii. S. 316-318. 



