

PHASES OF A SINGLE CONTRACTION. 461 



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 rota- 

 tion 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 in the following wood-cuts are drawn with the Pendulum 

 Myograph. 



Du Bois-Reymond draws muscle curves on the smoked surface 

 of a small glass plate contained in a frame, which is shot by. the 

 force of a spiral spring along tense wires, and on its way breaks 

 the contact. The trigger used for releasing the spring sets a 

 tuning-fork at the same time vibrating. 



SINGLE CONTRACTION. 



In response to a single instantaneous stimulus, such as the 

 making or breaking of an electric current, a muscle gives a mo- 

 mentary twitch or spasm, commonly spoken of as a single con- 

 traction, which is of so short duration that, without the graphic 

 method of recording the motion, we could not appreciate the 

 phases which are seen on the curve. 



