THE STUDY OP MUSCLE PHrSIOLOGY. 185 



Fig. 173.— Diagrammatic representation of the pendulum myogjraph. The smoked- 

 g^lass plate, A, swings with a pendulmn, B. Before an experiment is commenced 

 the pendulum is raised up to the right and kept in position by the tooth, a, catch- 

 ing on the spring-catch, b. On depressing the catch, 6, the glass plate being set 

 free swings into the new position indicated by the dotted lines, and is held there 

 by the tooth, a', meeting the catch, b'. In tne course of its swing the tooth, o, 

 coming into contact with the projecting steel rod, c, knocks it to one side, into 

 the position indicated by the dotted Une, c'. The rod, c, is in electric continuity 

 with the wire, x,^ of the primary coil of an induction machine. In like manner 

 the screw, rf, is in electric continuity with the wire, y, of the same primary coil. 

 The screw, d, and the rod, c, are provided with platinum points, and both are in- 

 sulated by means of the ebonite block, e. The circuit of the primary coil to which 

 X and y belong is closed as long as c and d are in contact. When in its swing 

 the tooth, a', knocks c away from d, the circuit is immediately broken, and a 

 "breaking" shock is sent through the electrodes connected with the secondary 

 coil of the machine, and so through the nerve. A lever is brought to bear on the 

 glass plate, and when at rest describes an arc of a circle of large radius. The tun- 

 ing-fork, /(ends only seen), serves to mark the time (after Foster). 



Apparatus of this kind is not usually employed much for 

 experiments with muscle ; such an arrangement is, however, 

 shown in Fig. 170, in which also will he seen a metronome, the 

 pendulum of which, by dipping into cups containing mercury, 

 makes the circuit. Such or a simple clock may be utilized for 

 indicating the longer intervals of time, as seconds. 



A SINGLE SIMPIjE MUSCULAR CONTRACTION. 



Experimental Facts.— The phases in a single twitch or mus- 

 cular contraction may be studied by means of the pendulum 

 myograph (Fig. 173). It consists of a heavy pendulum, which 

 swings from a position on the right to a corresponding one on 

 the left, where it is secured by a catch. During the swing of 

 the pendulum, which carries a smoked-glass plate (by means 

 of arrangements more minutely described below the figure), a 

 tuning-fork writes its vibrations on the plate, on which is in- 

 scribed the marking indicating the exact moment of the break- 

 ing of an electric current, which gives rise to a muscle contrac- 

 tion that is also recorded on the plate. 



The tracing on analysis presents : 1. The record of a tuning- 

 fork making one hundred and eighty vibrations in a second. 

 2. The parallel marking of the lever attached to the muscle 

 before it began to rise. 3. A curve, at fl.rst rising slowly, and 

 then rapidly to a maximum. 4. A curve of descent similar in 

 character, but somewhat more lengthened. 



We may interpret this record somewhat thus : 1. A rise of 

 the lever answering to the shortening of the muscle to which it 

 is attached following upon the momentary induction shock, 

 as the entrance of the current into the nerve, the stimulation of 

 which causes the contraction, may be called. 2. A period before 



