470 ELECTRO-PHYSIOLOGY CHAP. 



(as may easily be obtained by freezing thin layers of water) 

 as carefully as possible between the tongue and the leading-off 

 electrode. The current will then sink almost instantaneously to 

 zero, and is, as a rule, reversed in a few seconds. The new out- 

 going current may sometimes be of such dimensions that the scale 

 flies out of the field. If the single application of ice is not 

 sufficient, repetition of the treatment is sure to be success- 

 ful. After the ice has melted, the reversed current generally 

 diminishes rapidly, and finally turns round again as an entering 

 current. The diminution, which occurs more rapidly at first than 

 later, is not always uniform, but takes place with more or less 

 considerable oscillations. 



If the facts previously communicated are decidedly in favour 

 of the view that we here have mainly an effect of cooling, the 

 obvious objection must be answered that contact of the electrode 

 with the melting ice might give rise to a " thermo-current." This 

 conjecture is the more probable, since currents are actually known 

 to exist in consequence of the unequal warmth of the leading-off, 

 unpolarisable electrodes. Not merely are important thermo- 

 electric effects caused by unequal temperature in the two tubes 

 containing the glass-rods, but as found by Worm-Miiller and 

 verified by Griitzner a weaker " thermo-current," reversed in direc- 

 tion, may also arise between the clay plug saturated with NaCl 

 solution, and the solution of zinc sulphate. It passes from zinc 

 sulphate to clay, with an E.M.F. of 0'002 Dan. at 35 difference 

 of temperature. Control experiments, effected for the most part 

 with the clay block alone, as well as with dead, electrically in- 

 effective preparations of the tongue placed upon it, gave only 

 weak deflections in the same direction as before the experiments 

 in question, i.e. the cooled electrodes were, so to speak, weakly 

 positive. There is not, however, the smallest reason to refer the 

 very marked action of normal preparations to this cause. Apart 

 from all the other reasons that have been given, it is only 

 necessary to point out that the full effect of the outgoing current 

 appears also in the case in which the brush -electrode is first 

 brought into contact with the tongue some time after it has been 

 laid upon ice (after removing the water of liquefaction), when a 

 marked deflection at once follows in the expected direction, and 

 finally drives the scale off the field which can hardly, in this 

 case, correspond with any difference in temperature. Moreover, 



