196 SECONDARY ELECTROMOTIVE PHENOMENA IN 



repeatedly taken up the investigation as my views and methods 

 improved, and innumerable experiments on polarisation of nerves 

 have been lying for years in my note-books. 



Among other things I had already, in the years 1857 and 1858, 

 completed a table which exhibited the secondary electromotive 

 actions in nerves for a series of times of closure and current densi- 

 ties in both directions. The experiments were made with the nerve- 

 multiplier, the two sciatic nerves of a frog laid together being 

 used. A new pair of nerves was employed for each time of closure, 

 and each current density in each direction. Pfliiger, who was 

 then in Berlin, had the great goodness to assist me in these 

 experiments. The table for nerves suffered in the same way as 

 that traced out for muscles two years before, from all the faults 

 which were attached to my results before the discovery of unpolaris- 

 able electrodes, of physiological salt clay, of the method of compen- 

 sation and of the aperiodic galvanometer, besides which the strength 

 of the primary current was not regularly nor closely enough 

 watched. In spite of this I am obliged to make use of the older 

 table, as it has not yet been possible for me, as in the case of 

 muscles, to replace it with one less faulty. As, however, the 

 results of the older table of nerves resemble very much those of the 

 new table of muscles, perhaps the evil is not so great. Indeed the 

 graphic representation given in Figs. 5 and 6 of the polarisation- 

 curves, drawn relatively to the times of closure and opening, apply 

 nearly as well to nerves as to muscles. Current densities less than 

 a certain amount only give negative polarisation. With greater 

 current densities of from 5 to 5 Groves, and very short time 

 of closure, purely positive polarisation appears. With a somewhat 

 longer time of closure, which amounted to perhaps 0-2 second, 

 the polarisation in nerves was already in opposite directions, that is 

 to say, a positive deflection immediately succeeded a negative one. 

 If the time of closure amounted to more than a second, the polar- 

 isation was purely negative. I obtained the strongest positive 

 polarisation with a very short closure, from 25 to 30 Groves ; as 

 in the case of muscle, the force remained apparently below that of 

 the current of the nerve at rest. The strongest negative action 

 resulted, exactly as in muscle, from the passage of relatively 

 weaker currents for a longer time. After 45' five Groves, after 

 15' seven Groves, after 5' ten Groves swung the needle against 

 the stop of the multiplier, that is, a stronger action was produced 

 than by the nerve-current. Here also, as in muscle, the observ- 



