ELECTRICAL CURRENTS IN NERVE AND MUSCLE. 555 



while the surface is in connection with the other (Nobili, Matteucci, du Bois- 

 Reymond). The direction of the current is from the (positive) longitudinal section 

 to the (negative) transverse section in the conducting wires (i.e., within the muscle 

 itself from the transverse to the longitudinal section (figs. 380, I, and 399, I)). 

 This current is stronger the nearer one electrode is to the equator, and the other 

 to the centre of the transverse section ; while the strength diminishes, the nearer 

 the one electrode is to the end of the surface, and the other to the margin of the 

 transverse section. 



Smooth muscles also yield similar currents between their transverse and longitudinal surfaces 

 (334, II. ). 



3. Weak electrical currents are obtained when (a) two points at unequal 

 distances from the equator are connected ; the current then passes from the point 

 nearer the equator ( 4- ) to the point lying further from it ( - ), but of course this 

 direction is reversed within the muscle itself (fig. 399, II, ke and le). (b) Similarly 

 weak currents are obtained by connecting points of the transverse section at 

 unequal distances from the centre, in which case the current outside the muscle 

 passes from the point lying nearer the edge of the muscle to that nearer the centre 

 of the transverse section (fig. 399, II, i, c). 



4. When two points on the surface are equidistant from the equator (fig. 399, 

 I, x, y, v, z, II, r, e), or two equidistant from the centre of the transverse section 

 (II, c) are connected, no current is obtained. [Because the points are iso-electrical, 

 that is of equal potential.] 



5. If the transverse section of the muscle be oblique (fig. 399, III), so that the 

 muscle forms a rhomb, the conditions obtaining under III are disturbed. The 

 point lying nearer to the obtuse angle of the transverse section or surface is positive 

 to the one lying near to the acute angle. The equator is oblique (a, c). These 

 currents are called "deviation currents or inclination currents" by du Bois-Reymond, 

 and their course is indicated by the lines 1, 2, and 3. 



The electro-motive force of a strong muscle-current (frog) is equal to 0*05 to 0*08 of a 

 Daniell's element ; while the strongest deviation current may be 0*1 Daniell. The muscles of 

 a curarised animal at first yield stronger currents ; fatigue of the muscle diminishes the strength 

 of the current {Roeber), while it is completely abolished when the muscle dies. Heating a 

 muscle increases the current ; but above 40 C. it is diminished {Steiner). 

 Cooling diminishes the electro-motive force. The warmed living mus- 

 cular and nervous substance is positive to the cooler portions {Her- 

 mann) ; while, if the dead tissues be heated, they behave practically 

 as indifferent bodies as regards the tissues that are not heated. 



6. The passive nerve behaves like muscle, as far as 2, 3, 

 and 4 are concerned. 



The electro -motive force of the strongest nerve-current, according S 

 to du Bois-Reymond, is 0*02 of a Daniell. Heating a nerve from 15 to 

 25 C. increases the nerve-current, while high temperatures diminish 

 it {Steiner). 



7. If the two transversely divided ends of an excised nerve, 

 or two points on the surface equidistant from the equator, be 

 tested, a current the axial current flows in the nerve-fibre 

 in the opposite direction to the direction of the normal impulse 



in the nerve ; so that in centrifugal nerves it flows in a cen- -_ 



, , 1 j. ,. , . , , , . , . , Nerve-muscle prepara- 



tnpetal direction, and in ceutripetal nerves in a centrifugal tion of a iY ^ a l F 



direction (Mendelssohn and Christiani). femur ; S, sciatic 



The electro-motive force increases with the length of the nerve and "erve ; I, tendo Ach- 

 with the area of its transverse section. Fatigue {e.g., tetanic stimula- na- 

 tion) weakens it, especially in motor nerves, and to a less extent in centripetal nerves. 



[Nerve-Muscle Preparation. This term has been used on several occasions. It 

 is simply the sciatic nerve with the gastrocnemius of the frog attached to it (fig. 401). 



