240 PHYSIOLOGY OF MUSCLES AND NERVES. 



lecules combined in a particular way, many of which, 

 in combination, form a muscle-molecule or a nerve- 

 elemeiit respect ively. 



Wu have learned to regard the negative variation of 

 the muscle- or nerve-current as a movement of these 

 muscle- or nerve-molecules respectively, in consequence 

 of which the differences in tension between the longi- 

 t ud i mil and cross-sections become less. In explanation 

 of the electric phenomena of electrotonus, we may now 

 assume that under the influence of continuous electric 

 currents the nerve-molecules assume a different relative 

 position by reason of which the distribution of the 

 tensions on the outer surface of the nerve is (limited. 

 This changed position is retained as long as the electric 

 current flows through the nerve, and disappears more 

 or less rapidly after the opening <>f the current. At 

 first it takes effect only within the electrodes, but it 

 propagates itself through the extrapolar portions, be- 

 coming gradually weaker the further it is from the 

 electrodes. In illustration of this conception, we may 

 avail ourselves of the comparison which we have already 

 made of the nerve-molecules with a series of magnetic 

 needles. When the position of some of the needles in 

 the centre of such a series is changed, owing to some 

 external influence}, those needles which lie more on the 

 outside of the series must be turned to an extent de- 

 creasing ^ it h their distance from the centre. Or we 

 may al-o refer to the conception which physicists have 

 formed of the so-called elect r. .lysis, the analysis of a 

 Huid bv an electric current. All these analogies can 

 only explain the process in so far that \ve ivoignise how 

 an electric current is capable of causing a change in the 

 relative po<iti,,n of the muscle- and nerve-molecules, 



