OF MOVEMENT IN ANIMALS. 



33 



theless retain for several hours the circulation of the blood, 

 and the power of motion under the influence of electric 

 discharges. An electric excitator conveys the current from an 

 induction coil to the nerve of the frog. 



In order to register these movements and to depict them 

 by curves which express their different phases, they are trans- 

 mitted to the m3^ograph in the manner already described. 

 The tendon of the muscle is cut, and connected by a wire 

 which is fastened at the other end to the lever of the 

 registering apparatus ; the latter moves in a horizontal plane, 

 when the contractile force of the muscle is exerted upon it. 

 As soon as the muscle ceases to act, the lever returns, under 

 the pressure of a spring, to its original position. At the free 

 extremity of the lever is a point w^hich traces, on a turning 

 cylinder covered with smoked paper, the motions produced by 

 the alternate contraction and relaxation of the muscle. 



When the cylinder is motionless, the lever traces, for each 

 muscular shock, a straight line which expresses (by amplifying 

 it in a known proportion) the extent of the contraction of the 

 muscle. Several authors limit themselves to this kind of 

 myography, by which they ascertain the variations produced by 

 different influences in the intensity of muscular action. By 

 giving the cylinder a rapid rotatory motion, a curve is obtained 

 which expresses by its height the extent of the contraction, 

 and indicates by its inclination, which constantly varies, the 

 speed with which the muscle passes through the different 

 phases of the shock. Finally, in order to obtain, without 

 confounding them, a great number of successive tracings, 

 the foot of the myograph is placed upon a little railroad 

 which works parallel to the axis of the cylinder. The 

 writing point then traces an indefinite spiral all round the 

 cylinder, and on this spiral a number of regularly gradu-ated 

 curves (Fig. 5) are traced, answering to a series of electric 

 excitations produced at equal intervals ; each of these curves 

 corresponds with one of the electric shocks. 



If the speed with which the cylinder turns be augmented 

 or diminished, a change ensues in the appearance of the 

 curveSj which necessarily occupy a greater or less space on 

 the paper, but if a uniform speed in the rotation of the 

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