30 HAND-BOOK OF PHYSIOLOGY. 



lever. In this arrangement the muscle is in situ, and the nerve disturbed 

 from its relations as little as possible. 



The muscle may, however, be detached from the body with the lower 

 end of the femur from which it arises, and the nerve going to it may be 

 taken away with it. The femur is divided at about the lower third. The 

 bone is held in a firm clamp, the nerve is placed upon two electrodes con- 

 nected with an induction apparatus, and the lower end of the muscle is 

 connected by means of a ligature attached to its tendon with a lever 

 which can write on a recording apparatus. 



To prevent evaporation this so-called nerve-muscle preparation is placed 

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

 paper saturated with saline solution. 



EFFECT OF A SINGLE INDUCTION SHOCK. 



Taking the nerve-muscle preparation in either of these 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. 281). 



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

 graph (Fig. 282). Here the movement of the pendulum along a certain 



FIG. 281. Muscle-curve obtained by the pendulum myograph. s, indicates the exact instant of 

 the induction shock; c, commencement; and m x, the maximum elevation of lever; t, the line of a 

 vibrating tuning-fork. (M. Foster.) 



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. myograph is made to mark. The opening or breaking shock is sent 

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

 key (Fig. 282, C. ) in the primary circuit. 



Single Muscle Contraction. The tracings obtained in a manner 

 above described and seen in Fig. 281, may be thus explained. 



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



