478 



PENDULUM MYOGRAPH. 



whose axis, A, A, moves on friction rollers (fig. 321). At the lower swinging end are two glass 

 plates, G and G', fixed to a bearer, T. The plates can be adjusted by means of the screw, s, so 

 that several curves can be written one above the other. The plate, G', on the posterior surface 

 is merely a compensator, so that, when G is elevated, G' is lowered, and thus the duration of the 

 oscillation is not altered. The spring catches, H, H, which can be turned inwards or out- 

 wards, ate used to fix the pendulum by the teeth, a, a, when it is drawn to one side. The 

 pendulum is drawn to one side and fixed, a, in H, so that when H is pulled down, it is liberated 



and swings to the other side, where it 

 is caught by H at the opposite side. 

 In the improved form, the catches, H, 

 are made to slide along a rod like the 

 arc of a circle, so that the length of 

 the swing can be varied. As the pen- 

 dulum swings from one side to the 

 other, the projecting points, a, a, knock 

 over the contact key, b, and the cur- 

 rent is opened and a shock transmitted 

 to the muscle. The writing-lever to 

 which the muscle is attached is usually 

 a heavy one, and a style writes upon 

 the smoked surface of the glass. Of 

 course, when the pendulum swings, it 

 moves with uneqiial velocities at dif- 

 erent parts of its course.] 



[When using the pendulum myo- 

 graph to study a muscular contraction, 

 arrange it as in fig. 322. The frog's 

 muscle is attached to a writing-lever, 

 which is very like the lever in fig. 321, 

 while the style inscribes its movements 

 on the blackened plate.] 



[The pendulum is fixed in the catch, 

 C, as shown in the figure ; the key, 

 K.', is closed and placed in the primary 

 circuit, while two wires from the 

 secondary coil of an induction machine 

 are attached to the muscle. When 

 (c the pendulum swings, the projecting 

 tooth, S, knocks over the contact at 

 K', and breaks the primary circuit, 

 when a shock is instantly transmitted 

 through the muscle. Before stimu- 

 lating, allow the pendulum to swing 

 to obtain an abscissa. The time is 

 recorded by a vibrating tuning-fork, of 

 known rate of vibration, connected 

 with a Dupre's electric chronograph. 

 Dupre's chronograph is merely a small 

 electro-magnet with a fine writing 

 style attached, which vibrates when it 

 is introduced in an electrical circuit, 

 in which is placed a vibrating tuning- 

 fork. The signal vibrates just as often 

 as the tuning-fork.] 



[Du Bois' Spring Myograph. It 

 consists of a glass plate fixed in a 

 frame, and moving on two polished 

 steel wires, stretched between the supports A and B (fig. 323). At & is a spring which, when it 

 is compressed between the upright, B, and the knob, b, drives the glass plate from B to A. As 

 the plate moves from one side to the other, a small tooth, d, on its under surface, opens the 

 key, h, and thus a shock is transmitted to the muscle. The arrangement otherwise is the same 

 as for the pendulum myograph. The smoked glass plate is liberated by the projecting finger- 

 plate attached to the upright, A.] 



[Marey's Simple Myograph. The gastrocnemius is attached to a horizontal lever, which in- 

 scribes its movements on a revolving cylinder. This form of myograph, when provided with two 

 levers.is very useful for comparing the action of a poison on one limb, the other being unpoisoned. ] 

 [Pfliiger's stationary form is simply a Helmnoltz's myograph (fig. 320) arranged to record 



Fig. 321. 



Fick's pendulum myograph, as improved by v. Helm- 



holtz ( T \ natural size), side aud front view. 



