CONDUCTIVITY IN MUSCLE 447 



Another way of recording the contraction is by use of the pendulum myograph, figure 

 352. Here the swing of the pendulum along a certain arc is substituted for the clock- 

 driven 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 



FIG. 319. Arrangement of the Apparatus Necessary for Recording Muscle Contractions 

 with a Revolving Cylinder Carrying Smoked Paper. A, Revolving cylinder; B, the frog arranged 

 upon a cork-covered board which is capable of being raised or lowered on the upright, which 

 also can be moved along a solid triangular bar of metal attached to the base of the recording ap- 

 paratusthe tendon of the gastrocnemius is attached to the writing lever, properly weighted, 

 by a ligature. The electrodes from the secondary coil pass to the apparatus being, for the sake 

 of convenience, first of all brought to a key, D (Du Bois Reymond's); C, the induction coil; F, 

 the battery (in this figure a bichromate one); E, the key (Morse's) in the primary circuit. 



is sent into the nerve-muscle preparation by the pendulum in its swing opening a key, 

 figure 352, C, in the primary circuit. A muscle or its nerve is more irritable to an opening 

 shock than it is to a closing shock of the same strength, because the duration of the former 

 is shorter than that of the latter. 



Conductivity in Muscle. In an ameba or other simple undiffer- 

 entiated contractile protoplasmic unit a stimulus applied at any point is 

 quickly transmitted throughout the entire mass. Just so is it with differenti- 

 ated muscle. A stimulus applied at any point of a muscle will quickly be 

 propagated through the mass as far as there is protoplasmic continuity. In 

 cardiac muscle and in smooth muscle there is uninterrupted conduction from 

 cell to cell. But in voluntary muscle each fiber is physiologically isolated from 

 its neighbors. When a voluntary muscle fiber is stimulated either at the ex- 

 tremities or at its middle, the effect of the stimulus quickly passes through the 

 entire fiber, whether it arouses a distinct act of contraction or not. 



