ELECTRIC PHENOMENA IN MUSCLES. 



479 



and stimulated directly. These observations have generally been made on 



the gastrocnemius of the frog, the phenomena being recorded by a register- 



ing apparatus, the simplest form 



of which is the myograph of 



Helmholtz. This instrument is 



used in recording muscular con- 



tractions by causing the record- 



ing point to play upon a smoked 



paper moving at a known rate. 



If the muscle of the frog, slight- 



ly weighted, be stimulated by a 



single induction-shock, there is 



first a latent period, when there 



is no contraction, then a con- 



traction followed by relaxation, 



and finally a slight, elastic vibra- 



tion before the muscle becomes 



m , i FIG. loo. Diagram of the myograph of Helmholtz (Lan- 



quiescent. These phenomena dois). 



nrp illnstratprl in tbp onrvp p-ivpn M < muscle flxe(i b - v the clamp (K) by a portion of the fe" 

 irve gl\ei mur . F ^ recording point . PI counterpoise used to bal- 



in Fig. 156 in which, however, * f e w leTer ; w ' pan for weights ; s - S) su PP orts for 

 the latent period is not measured. 



In a muscle prepared in this way, the maximum of stimulation and the 

 maximum of power measured by a weight lifted can readily be ascertained, 

 and certain phenomena due to fatigue of the muscle have been observed. In 

 a fatigued muscle, the latent period is lengthened and the elevation of the 

 curve of contraction is not so high, showing a slower and longer action. 

 When a muscle is excited to tetanic contraction by a rapidly interrupted 

 current of considerable strength, the elevation produced by the initial con- 



traction is nearly vertical, 

 and is followed by a hori- 

 zontal straight line which 

 marks the tetanic condi- 

 tion. The phenomena in- 

 duced by direct stimulation 

 of muscles are somewhat 



IG. .-urve o a snge muscuar conracon anos. PY atr(rprniWl whpn tnp stim- 



A F, abscissa ; A C, ordinate ; A B, latent period ; B D, period of exaggerated WD 



contraction ; D E, period of relaxation ; E F, elastic vijra- ulug IS apl)lied to the mo- 

 tion. * 



tor nerve. 



Electric Phenomena in Muscles. It was ascertained a number of years 

 ago, by Matteucci, that all living muscles present electric currents. The 

 direction of these currents is from the longitudinal surface to the transverse, 

 or cut surface of the muscle, as is shown in Fig. 157. A simple method 

 of demonstrating the muscular current is to prepare the leg of a frog with 

 the crural nerve attached, and to apply one portion of the nerve to the 

 deep parts of an incised muscle and the other to the surface. As soon as 

 the connection is made, a contraction of the leg takes place. The current 



FIG. \m.-Curve of a single muscular contraction (Landois). 



