322 ELECTRO-PHYSIOLOGY CHAP. 



artificial cross -sections, while the upper surface (the "natural 

 longitudinal section " of du Bois) corresponds with the natural, 

 uninjured surface of the muscle. If unpolarisable electrodes are 

 so applied to the muscle -prism that the one leads off from the 

 artificial cross-section, the other from the middle of the natural 

 longitudinal section, it will be found, with a properly sensitive 

 galvanometer in the circuit, that there is invariably a pronounced 

 deflection, i.e. a current, which flows in the leading -off circuit 

 from longitudinal to transverse section, in the muscle on the 

 contrary from cross-section to longitudinal surface. 



Since any point of the longitudinal section, when connected 

 with any point of the transverse section, invariably gives a 

 current in the same direction, it may be stated generally that the 

 entire surface of the muscle cylinder is positive, and every cross- 

 section of the same negative in potential. It soon appears, 

 however, that the distribution of potential is unequal ; if the 

 muscle cylinder is conceived as divided in two halves, by a 

 plane parallel with its ends, and passing through the centre, the 

 greatest positive potential at the surface corresponds with the 

 " equator," i.e. the circumference of this section. From the equator 

 the positive potential on either side declines unequally, i.e. falls 

 more rapidly towards the end-surfaces, until at the margin between 

 longitudinal and transverse section it becomes practically zero. 

 Every line of potential, or isoelectric curve, therefore, forms a circle 

 parallel with the equator. The negative potential always decreases 

 at the ends, on either side, from centre to periphery. It is easy to 

 see from this distribution of potential that the magnitude of decline 

 may vary considerably, according to the position of the electrodes 

 of the leading -off circuit, so that the lines of current can 

 fall into a strong, weak, or ineffective arrangement. There will 

 obviously be no current on leading off from two points of the 

 equator, or any isoelectric curve parallel with it ; nor from points 

 of the longitudinal section symmetrical with the equator, or 

 corresponding points of the terminal sections. On the other 

 hand, a weak variation appears on leading off from two points of 

 the longitudinal section asymmetrical with the equator, or two 

 asymmetrical points of the section itself, or from both artificial 

 cross-sections. Fig. 102 gives a schematic representation of all 

 these possible cases ; a, b, c, d stand for sections of the muscle 

 cylinder ; the arrows show the direction of current flowing into 



