General physiology; an outline of the science of life . ically positive, the end of the zincelectrically negative. If the two ends beunited by a metallic conductor, such as awire, at the moment when the union isestablished, the electrical tension becomesequalised. Since, however, the tension is being constantly renewedat the place of contact of the metals with the liquid, there results acontinuous equalisation, which is termed a constant galvanic continuity of copper, wire, zinc, liquid, and copper, forms in acertain sense a closed circuit, in which the current flows. Thisgalvanic
General physiology; an outline of the science of life . ically positive, the end of the zincelectrically negative. If the two ends beunited by a metallic conductor, such as awire, at the moment when the union isestablished, the electrical tension becomesequalised. Since, however, the tension is being constantly renewedat the place of contact of the metals with the liquid, there results acontinuous equalisation, which is termed a constant galvanic continuity of copper, wire, zinc, liquid, and copper, forms in acertain sense a closed circuit, in which the current flows. Thisgalvanic current has always the same direction ; outside theliquid it flows from the copper, the positive pole, through the wireto the zinc, the negative pole. In the liquid its direction isevidently reversed; from the zinc, through the liquid, back to thecopper ; but this reversal need occasion no confusion, since it iscustomary to term the poles outside the liquid the positive andnegative poles. The copper is the positive, the zinc the negative 1 Cf. p. Fig. 188.—Galvanic free pole of the zinc ( —)is joined to the free pole ofthe copper (+) by a wire ; acircuit is thus formed, inwhich the direction of thecurrent is indicated by thearrows. STIMULI AND THEIR ACTIONS 405 pole, or, as it is also said in order to express in words the directionof the current, the copper ( + ) is the anode, the zinc ( —) thehathode. This primitive form of galvanic element, upon which, slightlymodified, is based the very powerful chromic acid clip-element inwhich carbon and zinc dip into dilute chromic acid, has provedfor many purposes unserviceable. If the circuit be kept closedfor a considerable time, , if the metallic union between the twoends of the metals be not interrupted, or, as is said, the currentbe not broken, it is found that the current is not so strong as atthe beginning. This depends upon the fact that certain substances,the so-called polarisation-prodiicts, have be-
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