Phyxi(J<t<iy of the Muscles. 495 



Electric shucks arc best applied by induction. (Sec fig. 144. The 

 coil b is placed inside of t and then the circuit through b and the battery 

 a is arranged to be opened and closed readily with a key.) The sudden 

 interruption ( unclosing ) of the current through the active coil fr, pro- 

 duces an instantaneous shock through the silent coil c and a sudden con- 

 traction of the muscle attached to it, another shock and another sud- 

 den contraction occurs when the current in the coil b is again closed. A 

 direct current from the battery itself is also capable of acting as an ir- 

 ritant on muscle, a pulsation generally occurring when the current is in- 

 terrupted, and again when it is closed or connected. If the current 

 remains closed, the muscle after the first contraction will partially relax 

 and remain so during the passage of the current. But by placing a 

 small ratchet wheel in the line of the current by the turning of which 

 with a crank the operator can rapidly break and connect the current, the 

 irritations can be repeated more rapidly than the muscle can recover 

 from the shocks, so that permanent rigid contraction or tetanus is pro- 

 duced. Muscular action, therefore, is in the form of a sudden pulsation 

 or the enduring tetanus ; which is really a succession of pulsations with- 

 out sensible interval. Every muscle is capable of accomplishing a cer- 

 tain amount of work by contraction. The following table shows what 

 was accomplished by a particular detached muscle before its contractility 

 was exhausted. The muscle was suspended and weights attached to it. 



In this particular case the best results came from the work expended 

 on 150 grammes. The thicker the muscle the greater the weight it can 

 raise ; the longer- the muscle fibres the higher the weight can be raised. 



In the foregoing experiment the muscle action was upon pulsation, 

 not tetanus. The work done in tetanus is in first raising the weight 

 and afterwards holding it up. The labor of raising the weight under 

 the stimulus of a single pulsation as above is accompanied by heat or 

 molecular change in the ultimate molecules of the muscle, which change 

 is not noticed in the table and would not be easy to estimate. It is one 

 of the forms of energy exhibited in the movement of the muscle, the 

 other demonstration of energy being the visible contraction and lifting 

 of the weight, which alone is shown in the table. In tetanus when after 

 the weight is lifted, it continues to be held up by the continued irrita- 

 tion of the muscle, the amount of heat disengaged is greatly increased ; 

 the appreciable sign of the work done in the holding up being the in- 

 creased molecular vibrations in the muscle itself, indicated by the sen- 



