32 PHYSIOLOGY OF MUSCLES AND NERVES. 



An electric current from the battery itself is also 

 capable of acting as an irritant on muscle. If the poles 

 of the battery are connected with the muscle, a constant 

 current passes through it. If one of the connecting 

 wires consists of two parts, a capsule filled with quick- 

 silver may be inserted between the cut ends. One end 

 of the wire must be allowed to remain immersed in the 

 quicksilver ; the other end must be bent into the form 

 of a hook so as to allow it to be easily immersed in, and 

 again withdrawn from, the quicksilver. This makes 

 it easy to close the current within the muscle, and 

 to interrupt it again at pleasure. At the moment 

 at which the current is closed, a pulsation is observed 

 entirely similar to that which would be produced by 

 an electric shock. The muscle contracts, and the disc 

 is jerked upward and then falls again. But it does 

 not return quite to its original position ; it remains 

 somewhat raised, thus showing that the muscle is now 

 continuously contracted ; and this contraction lasts as 

 long as the current passes iminterruptedly through the 

 muscle. 



If the current is interrupted, a pulsation which 

 jerks the lever upward is sometimes but not always 

 observable ; the muscle then, however, resumes its 

 original length, which it retains until it is irritated 

 anew. 



2. These experiments show that muscle exhibits 

 two forms of contraction : the one, which we called pul- 

 sation, is of short duration ; the other, which is produced 

 by a constant electric current, endures longer. This 

 more enduring form of contraction may, moreover, be 

 yet more conveniently produced by allowing an irritant 

 such as in itself would only produce a single pulsation 



