268 



GENERAL PHYSIOLOGY 



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products of the moist conductor appear at the two ends of the 

 wire, the electrodes, and accumulate there. The precipitation of 

 these products at the two poles produces an electric tension that 

 leads to a current, the so-called polarisation-current, flowing in a 

 direction contrary to the original one. It is evident that the 

 stronger the polarisation-current becomes, the more must the 

 intensity of the original current be thereby diminished. If, 

 therefore, a current be led off from a living tissue by means of 

 metallic electrodes, after a short time a polarisation-current 

 appears that completely obliterates the tissue-current. In order 



to avoid this inconvenience, so-called 

 non-polarisaile electrodes have been con- 

 structed, which consist of non-metallic 

 conductors. The most convenient of 

 these non-polarisable electrodes are the 

 brush electrodes suggested by Fleischl, 

 which consist of a glass tube closed at 

 one end by a stopper of plastic clay, 

 and filled with a concentrated solution 

 of sulphate of zinc. A short, soft, 

 pointed camel's-hair brush is stuck into 

 the stopper, and into the solution of 

 zinc sulphate there is dipped an amal- 

 gamated zinc rod, to which the wire is 

 fastened (Fig. 122). The brushes of two 

 such electrodes, each of which is attached 

 to a movable stand, are laid upon the 

 living tissue. Experience has shown 

 that in this manner the disturbing pheno- 

 mena of polarisation are avoided. 



In the electrical phenomena of most 

 animal- and all plant-tissues the currents 

 are always so feeble that especially sensi- 

 tive apparatus is necessary for their de- 

 monstration ; but in the interesting elec- 

 trical fishes there are currents of extraordinary strength, although 

 the well-known tale of Alexander von Humboldt, that the South 

 American electric eel is able to stun horses by its shocks must 

 rest upon an error. In contrast to the currents of other tissues, 

 those of the electric fishes are characterised chiefly by their short 

 duration and great intensity ; the}- appear as brief, strong electric 

 shocks, which can be given off by the animal several times in 

 succession, either spontaaeouslj' or upon stimulation. This is 

 comprehensible when it is considered that the production of 

 electricity in these animals serves as a means of defence, which 

 has become differentiated to this great efficiency during the 

 evolution of the race. In accordance with this fact special 



Fig. 121. — Schematic. SartoHus 

 muscle of the frog. At the two 

 ends are the bony attachments. 

 /. When uninjured and at rest, it 

 is without a current. //. When 

 injured (cut across), it shows a 

 current, the injured place being 

 negative. ///. When active (a 

 contraction wave is passing from 

 the right through the muscle), it 

 shows a current ; the active place 

 is negative. 



