204 SECONDARY ELECTROMOTIVE PHENOMENA IN 



strength of the polarising- current. 2. If the polarising current 

 acts during an unequal length of time on the nerves under other- 

 wise unaltered circumstances, the polarisation increases ; it rises at 

 first faster, and later more slowly, finally reaching its maximum 

 extremely slowly. 3. If the polarising current is opened, the 

 polarisation instantly reaches its highest amount, and after that 

 sinks continuously. This decrease is at first very rapid, later on 

 always slower, so that the polarisation persists a long time after 

 the opening of the polarisation-current, and only approaches the 

 zero point asymptotically.' Tigerstedt would certainly have met 

 with the internal positive polarisation of nerves in his carefully- 

 conducted experiments, if he had employed greater current den- 

 sities and a shorter time of closure. As it was, however, he 

 remained, like his predecessors, on the further side of the critical 

 time of closure. Neither Hermann, Fick, nor Tigerstedt had a gal- 

 vanometer in the battery circuit. I do not think that this was of 

 any importance in their experiments, but I would caution any one 

 from engaging in a series of experiments with strong currents and 

 long times of closure without following this rule. (Sect. 6.) 



17. On the Influence of the Direction of the Primary Current 

 on the Secondary Electromotive Actions of Nerves. 



It was the desire and hope of communicating something definite 

 about the dependence of internal positive polarisation of nerves on 

 the direction of the polarising current, that chiefly withheld me 

 from publishing my investigations in their present condition. The 

 remarkable fact that the greater strength of positive polarisation of 

 muscle in the direction from the equator, in or near which the hilus 

 is situated, towards the ends (Sect. 9), led me for a time to suppose 

 that the intra-muscular nerves were concerned, and that they 

 underwent a stronger positive polarisation in a centrifugal direc- 

 tion. This led me to the idea of experimenting as to how the 

 motor and sensory roots of the spinal nerves would behave, in 

 relation to internal polarisation. 



Polarisation experiments on the roots are naturally made much 

 more difficult by their shortness. The first requisite is to procure 

 the largest possible frogs. In 1857 I measured a R. esculenta of 

 298 mm. and one of 305 mm. from the point of the nose to the 

 longest toe. I succeeded, however, in applying four wedge-shaped 



