PHENOMENA OP MUSCLE AND NERVE. 285 



+ after-effect might be caused by ordinary polarisation with this 

 arrangement, supposing, for instance, enveloping layers of badly- 

 conducting polarised portions of tissue to be present. Should the 

 + after-current also appear by leading-off on the same surface 

 with the leading-in electrodes, then this possibility is removed. 

 As a matter of fact this is the case : no marked difference appears 

 between the results obtained with contacts on the same and on 

 opposite surfaces. 



The simplest arrangements sufficed to show the phenomenon. 

 A Pohl's commutator without cross-wires served to close the 

 galvanometer-circuit immediately after the battery-circuit was 

 opened, the commutator being coupled up by I, 2, with the battery, 

 by 4> 5 with the galvanometer-circuit. In my 

 former experiments upon extrapolar after-currents 1 

 this method was not satisfactory, owing to insuffi- 

 ciency of insulation; but the effects of insufficient 

 insulation are much less marked in the case of intra- 

 polar than in that of xtrapolar after-currents. Sub- 

 sequently the wooden reverser was replaced by a paraffin one. 

 The switching from battery to galvanometer-circuits was effected 

 as quickly as possible by hand, in the case of long closures by a 

 clock. 



In muscle, after a very short closure, the after-current appeared 

 to be mostly diphasic 2 ; a quick, sometimes momentary being 

 followed by a long-enduring + deflection which mostly only 



1 ' Untersuchungenzur Physiologic der Muskeln und Nerven,' Part 3, Berlin, 1868 

 p. 71. 



2 It seems to me that du Bois-Reymond has seen this diphasic (doppelsinnig} effect 

 more seldom than I have, and the cause probably lies in the extreme lightness of the 

 magnet system of my galvanometer ; it weighs only 0-9 gr. (see ' Pfliig. Archiv,' 

 vol. xxi. p. 436). Besides this, very effectual damping gives aperiodicity with a 

 relatively slight amount of astasia : it is thus conceivable that a heavier or more 

 astatic system may not show the very small negative jerk of which my instrument 

 gives plain indications. 



It may also be noticed here that with rapidly vanishing polarisation-currents the 

 velocity of the movement of the magnet must largely influence the amount of the 

 deflection, since the current itself becomes smaller during the deflection. This 

 influence, as to which I have many times convinced myself, is rendered especially 

 predominant through aperiodicity. On this ground, as I have often seen, the deflec- 

 tions caused by rapidly decreasing polarisation-currents are not diminished by with- 

 drawal of the bobbin to the same extent as in the case of constant currents ; the 

 shorter time which the diminished deflection requires enables the maximum of deflec- 

 tion to coincide with a greater strength of current than would be the case if the 

 instrument were rendered more sensitive. 



