OF THE ELECTRICAL ORGAN OF TORPEDO MARMORATA. 
523 
latter reveal themselves as prolonged changes, in which the dorsal surfaces of the 
columns are galvan©metrically positive to the ventral. 
A polarising current directed through the tissue in the direction of that of the 
organ response is the most effectual for the production of the change in question. 
Such a polarising current has been termed by du Bois-Reymond “ homodromous” ; it 
will be denoted in this work by the sign ( + ), since the cathode of the polarising 
circuit is on the dorsal surface of the columns. A current oppositely directed through 
the organ columns will be denoted by the sign ( —). 
If the phenomena of electrolytic polarisation, and these only, are present in the led- 
through tract, then a (-f-) polarising current will be followed by a (—) after-effect, 
a ( —) polarising current by a (+) after-effect, the signs referring in all cases to the 
condition of the dorsal electrode. 
Such is the case in the following example, which is given to show the polarisable 
character of the tissue. 
A strip of organ, consisting of several entire columns, having been prepared from a 
small Torpedo, and measuring 13 mm. in length and 2 mm. in thickness, was jffaced 
upon a glass plate and led off as usual from the dorsal and ventral ends. Upon the 
kaolin plugs of the leading-off’ electrodes were placed the kaolin plugs of another pair 
of non-polarisable electrodes, which served to lead the polarising current through 
the tissue. A paraffin switch of the kind used by Hermann was introduced into 
the galvanometer and polarising circuits. By its movement the galvanometer circuit 
was broken, and the polarising circuit closed about afterwards; the return of the 
switch broke the polarising and then re-closecl the galvanometer circuit. The move¬ 
ment of the switch was effected in the one direction by the hand, in the other by an 
elastic spring. The sensibility of the galvanometer was the same as in the early 
experiments, and the falling time of the needle was fifteen seconds. The effect was 
therefore accurately indicated by reading the amount of the deflection every fifteen 
seconds. 
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