x ELECTROMOTIVE ACTION IN NERVE 317 



(as well as characteristic of the physical considerations which till 

 recently prevailed in physiology) to study the theories which 

 were subsequently expressed as to the nature of electrical ex- 

 citation in particular, from the starting-point of the molecular 

 hypothesis. In vol. i. of Funke's excellent text-book (2nd ed. 

 IS (3 3) the following characteristic statement occurs on p. 859 : 

 " The exciting electrical current disposes the molecules of the 

 nerve between the electrodes in a dipolar arrangement, on the 

 system of the voltaic pile ; the molecules which lie at the edge of 

 the dipolar layer first produced by the electrical current attract 

 those which lie beyond the electrodes, and are directed contrary 

 to the exciting current. These again act upon the next inverted 

 series, and so on, until all the molecules are arranged down to the 

 end of the nerve like a pile. It follows that at the moment 

 when electrotonus is produced in the tube of the nerve, a process 

 of transmission takes place, analogous with the course of a wave 

 along a trough filled with water. In this last case we learn from 

 physics that there is a progressive displacement of the single 

 particles of fluid, at a given rate, from the point at which the wave 

 is excited to the end of the trough : in nerve there is a progres- 

 sive displacement of the molecules from the excited spot to the 

 two ends in succession, in consequence of the electrical action at 

 a distance of each molecule upon its neighbours. The propaga- 

 tion of this molecular movement occurs like that of the wave of 

 water, with comparatively low and measured velocity. A process 

 of transmission corresponding in some degree with the negative 

 wave occurs in the nerve-tube at the moment when electrotonus 

 ceases. When the exciting current is interrupted, the molecules 

 between the electrodes return by virtue of an unknown directive 

 force to the peripolar arrangement; their directive action upon 

 those external to them consequently disappears the latter also 

 return to the peripolar disposition, along with those succeeding to 

 them, and so on to the end of the nerve. The attraction of the 

 molecules at the close of electrotonus (opening of the current) is 

 opposite in direction to that at its commencement ; the direction 

 of transmission is the same, analogously with the relations of the 

 positive and negative wave of water. We have already seen that 

 the beginning and end of electrotonus, the closure and opening of 

 the exciting current, are accompanied by a twitch of the muscle 

 connected with the nerve, i.e. that the muscle twitch due to the 



