GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 147 



the slit, it will influence the sensitized surface except where the mercury column inter- 

 venes ; the movements of the mercury will be photographed as a silhouette. 



2. Currents of Rest. — A normal resting nerve or muscle presents no dif- 

 ferences in electric tension and gives no evidence of electric currents, wherefore 

 we say it is iso-electric. If any part of the structure be injured, its electrical 

 condition is forthwith changed, and if the injured portion and some normal 

 part be connected with a galvanometer, an electric current is observed to flow 

 from the normal region to the point of injury. These muscle- currents were 

 discovered at about the same time by Matteucci and Du Bois-Reymond, and 

 the latter wrote a now celebrated treatise upon the electrical phenomena to be 

 observed in the nerve and muscle under varying conditions. 1 



Directions of Currents of Best. — If a striated muscle, with long parallel 

 fibres, such as the sartorius or the semimembranosus of a frog, be prepared 

 with care not to injure the surface, and then be given a cylindrical shape by 

 cutting oif the two ends at right an- 

 gles to the long axis, the piece Mill 

 present two cross sections of injured 

 tissue and a normal longitudinal sur- 

 face (see Fig. 64). If non-polarizable 

 electrodes, connected with the coils of 

 wire of a galvanometer, be applied to 

 various parts of such a piece of mus- 

 cle, it will be found that all points on 

 the longitudinal surfaces are positive 

 in relation to all points on the cross 

 sections, but that the differences of 

 tension will differ according to the 

 points which are compared. Suppose 

 that the cylinder be divided into 

 equal halves by a plane parallel to the 

 cut ends. Points on the line bound- 

 ing this plane, the equator, show the 



greatest positive tension, and the farther other points on the longitudinal sur- 

 face are from the equator the less their tension. Points on the cross section 

 show a negative tension, and this lessens from the centre to the periphery of 

 the cross section. Points on the cross section equidistant from the centre, or 

 on the longitudinal surface equidistant from the equator, have the same poten- 

 tial and give no current, while points placed unsym metrically give a current. 

 Splitting the cylinder by separation of the parallel fibres gives pieces of mus- 

 cle which show the same electrical peculiarities, and without doubt the same 

 would be true of separate muscle-fibres or pieces of fibres. 



Samjloff 2 says that the electro-motive force of the currents ordinarily 



1 Unterwchungen fiber thierische Etektricitat, Berlin, 1849. 

 - ^anijlotl': Pfluger'a Archiv, 189 ( J, Bd. Ixxviii. S. 1. 



Fig. 64.— Schema to show the direction of cur- 

 rents to be obtained from muscle. The schema 

 represents a cylindrical piece of muscle with nor- 

 mal longitudinal surface (a, c and h, d), and two 

 artificial cross sections (a, 6 and c, d). The position 

 of the equator is shown by line e. The unbroken 

 lines connect points of different potential, and tin- 

 arrows show the direction which the currents 

 WOUld take were these points connected with a 

 galvanometer. The broken lines connect points 

 of equal potential from which no current would be 

 obtained. 



