THE MUSCULAR SYSTEM. 



411 



placed under a glass shade, the air in which is kept moist by means of 

 blotting paper saturated with saline solution. 



Effects of a Single Induction Shock. With a nerve-muscle pre- 

 paration arranged in either of the above ways, on closing or opening the 

 key in the primary circuit, we obtain and can record a contraction, and 

 if we use the clockwork apparatus revolving rapidly, a curve is traced 

 such as is shown in Fig. 288. 



Another way of recording the contraction is by the pendulum myo- 

 graph (Fig. 289). Here the movement of the pendulum along a certain 

 arc is substituted for the clockwork movement of the other apparatus. 

 The pendulum carries a smoked glass plate upon which the writing lever 

 of a rnyograph is made to mark. The opening or breaking shock is sent 



Fia. 287. Arrangement of the apparatus necessary for recording muscle contractions with a 

 revolving cylinder carrying smoked paper. A, revolving cylinder; B, the frog arranged upon a 

 cork- covered board which is capable of being raised or lowered on the upright, which also can be 

 mov 

 tendon of the gastrocnemi 



- , 



ed along a solid triangular bar of metal attached to the base of the recording apparatus the 

 don of the gastrocnemius is attached to the writing lever, properly weighted, by a ligature. 

 The electrodes from the secondary coil pass to the apparatus being, for the sake of conveni- 

 ence, first of all brought to a key, D (Du Bois Reymond's); C. the induction coil; F, the battery (in 

 this fig. a bichromate one) ; E, the key (Morse's) in the primary circuit. 



into the nerve-muscle preparation by the pendulum in its swing opening 

 a key (Fig. 289, C.) in the primary circuit. 



Single Muscle Contraction. The tracing obtained of a single 

 muscle contraction (muscle curve) is seen in Fig. 288, and may be thus 

 explained. 



The upper line (m) represents the curve traced by the end of the lever 

 after stimulation of the muscle by a single induction-shock: the middle 



