458 MANUAL OF PHYSIOLOGY. 



the touch depends on the difference of tension of the serai-fluid 

 contractile substance within the muscle sheath. 



THE GRAPHIC METHOD OF KECORDING MUSCLE CONTRACTION. 



In order to study the details of the contraction of muscle, the 

 graphic method of recording the motion is applied. The curve 

 may be drawn on an ordinary cylinder moving sufficiently rapidly. 

 Where accurate time measurements are required it is better to 

 use one of the many special forms of instruments, called myographs, 

 made for the purpose. The principle of all these instruments is 

 the same ; namely, an electric current, which passed through the 

 nerve of a frog's muscle connected with the marking lever, is 

 broken by some mechanism, while the surface is in motion ; the 

 exact moment of breaking the contact can be accurately marked 

 off on the recording surface by the lever which draws the muscle 

 curve before the instrument is set in motion. The rate of motion 

 is registered by a curve drawn by a tuning fork of known rate of 

 vibration. 



In order that the muscle-nerve preparation may not be injured 

 by the tissues becoming too dry, it is placed in a small glass 

 box. the air of which is kept moist by a damp sponge. This 

 moist chamber is used when any living tissue is to be protected 

 from drying. 



The first myograph used was a complicated instrument devised 

 by Helmholtz ; in which a small glass cylinder is made to rotate 

 rapidly by a heavy weight, and when a certain velocity of rotation 

 is attained, a tooth is thrown out by centrifugal force, which 

 breaks the circuit of the current passing through the nerve of the 

 muscle. The tendon is attached to a balanced lever, at one end 

 of which hangs a rigid style pressed by its own weight against 

 the glass cylinder. When the circuit is broken the muscle con- 

 tracts, raises the lever, and makes the style draw on the smoked 

 glass cylinder. 



Fick introduced a flat recording surface moving by the swing 

 of a pendulum, by which the abscissa is made a segment of a circle, 

 and not a straight line, and the rate varies, so that the different 

 parts of the curve have varying time-values. The curves given 



