ELECTROMOTIVE ACTION IN NERVE 301 



again charge h. 2 with hydrogen, and so on. The whole region 

 round A is, however so soon as a stationary condition has been 

 established charged (in a degree that diminishes with the distance) 

 with hydrogen, that round C with oxygen. The currents that 

 arise from these charges, and at the same time maintain them, can 

 be detected in a leading-off circuit," as indicated above (Hermann). 

 For the more exact investigation of these phenomena, which 

 are important to the theory of electrotonus, Hermann subse- 

 quently employed a model, in which the moist sheath was 

 replaced by a free fluid (saturated zinc sulphate). This circulated 

 in a glass tube (Fig. 216) with lateral openings, through which 

 he passed a platinum wire. Amalgamated zinc wires served as 

 the leading-in and leading-off electrodes. Apart from the facts 

 quoted above, this experiment showed that every interruption of 

 the wire (core-conductor), or of the liquid sheath, between the 

 polarised and led-off parts, hindered the production of the extra- 

 polar currents, which, for the rest, are proportional with the 

 polarising current. They coincide with the electrotonic incre- 

 mental current of medullated nerve, in so far that, with a given 

 distance between the two tracts, their intensity increases with the 

 length of area traversed (with uniform intensity of polarising 

 current). The currents are further present at the moment of 

 closure, and where the combination employed (e.g. platinum in 

 zinc sulphate or sulphuric acid) is polarisable on both sides, are of 

 equal strength at anode and kathode. On the other hand, the 

 extrapolar currents on the kathodic side fail altogether, or appear 

 only in the immediate vicinity of the pole, when the combination 

 polarises on one side (the anode) only e.g. zinc wire in H 2 S0 4 or 

 Nad, copper wire in H. 2 S0 4 or ZnS0 4 . Lastly, as in nerve, 

 so in the core-model, the extrapolar incremental current fails 

 altogether with transverse direction of current. 



In the year 1883 Hermann discovered on a core-model 

 (platinum in zinc sulphate), 2 metres long, on passing in frequent, 

 brief, constant currents of uniform direction, with Bernstein's 

 rheotome that, with a great distance between the polarised and 

 led-off parts, the electrotonic currents sometimes began, or at any 

 rate attained their maximum, only after the polarising current 

 had been opened, which obviously points to an undulatory character 

 of the corresponding galvanic processes. With a shorter distance 

 between exciting and galvanometer tracts, the maximum of homo- 



