104 PHYSIOLOGY OF MUSCLE AND NERVE 



This electrical difference persists as long as the injury. The same 

 conditions prevail in a degenerating muscle, its degenerated portion 

 being galvanometrically negative to its normal portion, but naturally, 

 these differences cease as soon as the degeneration has progressed 

 evenly throughout its substance. Dead tissue gives no current. In 

 order to obtain the current of injury in an unmistakable manner, it 

 is best to employ a cylindrical muscle and to injure it by cutting trans- 

 versely across one of its ends. One non-polarizable electrode is then 

 placed against this cross-section, while the other is adjusted externally 

 upon the equator of the muscle. In 'explanation of this current 

 DuBois-Reymond has proposed the so-called molecular theory which 

 assumes that the muscle is built up of a seiies of the smallest possible 

 molecules which are electrically charged and are surrounded by an 

 indifferent conducting fluid. These individual molecular elements 

 are peripolar, i.e., their equatorial zones are positive and their polar 

 zones negative. The former are directed toward the surface and the 

 latter toward the cross-section of the muscle. Hermann's^ explana- 

 tion is based upon the so-called ''alteration theory" which assumes 

 that muscle tissue develops no electrical current as long as its chemical 

 constitution remains the same throughout its substance. Electrical 

 differences, however, arise immediately if the chemical equilibrium of 

 any of its zones is disturbed either by injury, degeneration or activity. 

 Oker-Blum^ claims that these differences in the electrical potential of 

 a muscle are dependent upon its varying concentration and are caused^ 

 therefore, by the speed of movement of its different ionic constituents. 

 Bernstein^ refers them to a process of dissociation. But these theories, 

 as well as the one advocated more recently by Overton'* are altogether 

 too incomplete and indefinite to be made the subject matter of a prof- 

 itable discussion for students. 



In 1842 Matteucci made the observation that if the sciatic nerve 

 of one leg is placed upon the muscles of the opposite leg, the muscles 

 of both legs may be made to contract by simply stimulating the sciatic 

 nerve on the normal side. This experiment, which is known as 

 the ''induced contraction" or "secondary tetanus," may also be per- 

 formed in the following manner (Fig. 59). Two muscle-nerve pre pa- 

 rations. (A and B) are placed near one another upon a glass plate in 

 such a way that the sciatic nerve of muscle B rests lengthwise upon the 

 body of muscle A, If the nerve of muscle A is now stimulated with a 

 weak induction shock, the reaction involves not only muscle A but 

 also muscle B. The essential point to be remembered about this 

 experiment which is usually designated as the rheoscopic frog prepara- 

 tion, is that muscle B is not stimulated directly by the current applied 

 to nerve A, but indirectly by the ^^ current of action' ' generated in 

 muscle A in consequence of its contraction. 



1 Handb. der Physiol., Leipzig, i, 1879, 235. 



2 Pfluger's Archiv, Ixxxiv, 1901, 191. 

 8 Ibid., xcii, 1902, 521. 



* Sitzungsb. der ph.-med. Gesellsch., Wurzburg, 1905. 



