458 



MUSCLE PHENOMENA. 



demonstrates the existence of an electric current flowing from the 

 normal to the cut portion. If the muscle is caused to contract, 

 the needle of the galvanometer will return to the position of rest. 

 The first current was formerly called the current of rest, but is now 

 known as the current of injury or demarcation current ; while the 

 second is the current of action, or negative variation current. 



Du Bois Reymond explained the current of rest by supposing 

 that in the normal muscle at rest there were electric currents due 

 to the fact that muscle was made up of electromotive molecules, 

 and that each of these molecules is positive at the center and 

 negative at the ends, and this difference of electric tension be- 

 comes manifest when the muscle is cut and the negative ends are 

 exposed. Hermann, however, denies the existence of currents in 



FIG. 266. Secondary tetanus (Lombard). 



normal muscle, and attributes their generation to the injury to the 

 muscle caused by its action, chemic changes being thus brought 

 about. Other injury than cutting will produce the same result, 

 and as these changes take place at the point between the normal 

 and injured tissue the term " demarcation" has been applied to 

 the current thus produced. 



It should be said, however, that there are authorities who hold 

 with Du Bois Reymond that normal muscle in a condition of rest 

 is the seat of electromotive forces, which require changed condi- 

 tions in muscle to bring them forth. 



It has been already stated that dead muscle is iso-electric ; 

 dead muscular tissue is, however, electrically negative to normal 

 living muscle. 



Secondary Contraction (Fig. 266). To demonstrate secondary 

 contraction two nerve-muscle preparations are made, and the 

 nerve of one is placed upon the muscle of the other. Such an 

 arrangement constitutes a physiologic rheoscope or rheoscopic frog. 

 When the nerve of the first preparation is stimulated, not only its 

 muscle, but also that of the second preparation, contracts. If the 

 stimulation is single, a secondary contraction or twitch results ; 

 while if the stimuli cause tetanus of the first muscle, there will 

 be secondary tetanus of the second muscle. 



