580 PHYSIOLOGY. 



battery), a deviation of the galvanometer-needle will be apparent, 

 showing a reversal of direction of current, as was the case with the 

 electrodes in water. To get rid of this current, due to polarization 

 of the electrodes by the tissue of the muscle or nerve, it w r as neces- 

 sary to employ electrodes which were unpolarizable. Eegnault found 

 these to be zinc immersed in a strong solution of zinc sulphate. 

 DuBois-Reymond constructed electrodes upon this plan. They are 

 usually made by taking two small pieces of glass tubing, open at both 



Fig. 216. Tetanizing Key of DuBois-Reymond. (After ROSEN- 

 THAL.) (From Mills's "Animal Physiology," copyright, 1889, by D. 

 Appleton and Company.) 



Wires may be attached at 6 and c. When d is down the current is "short- 

 circuited," i.e., does not pass through the wires, but direct from c through d to 

 6, or the reverse, since 6, c, d are of metal and, on account of their greater 

 cross-section, conduct so much more readily than the wires, a Is an insulating 

 plate of ebonite. This form of key is adapted for attachment to a table, etc. 



ends and curved. One end of the tube is plugged with modeling 

 clay, moistened with salt solution, and then the tube is filled with a 

 saturated solution of sulphate of zinc in which is immersed a rod of 

 amalgamated zinc and to which one of the wires of the circuit is 

 attached. The non-polarizable electrodes of Porter's are porous, 

 boot-shaped cups filled with saturated solution of sulphate of zinc, 

 in which is plunged a zinc rod. 



After v the use of the unpolarizable electrodes the boot should be 



