94 GENERAL PROPERTIES OF LIVING TISSUES 



diameter, in which is placed the zinc. The foot is 

 20 mm. long, measured from its junction with the 

 leg. In the foot is a well for normal saline solution 

 which shall keep the feet 'equally saturated. The 

 boots should ordinarily be kept in normal saline so- 

 lution. In use the hollow leg of the boot is half-tilled 

 with saturated solution of zinc sulphate and placed in 

 the clip. The well in the foot of the boot is now filled 

 with normal saline solution. If metal clips are used 



Fig. 23. Non-polarizable electrodes ; about 

 two-fifths the actual size. 1 



the boots should be mounted on separate rods, to 

 prevent the current passing through the unglazed 

 boot to the metal holder and thus to the other boot. 

 This difficulty is avoided by the rubber holders shown 

 in Fig. 24. The electrodes may be mounted on a 

 brass rod called the mounting-rod, or in the moist 

 chamber shown in Fig. 24. The boot electrodes 

 serve equally well for leading off the nerve or ra.ua- 



1 First described in " Science," 1901, xiv, pp. 567-570. The 

 well was added in Nov. 1905. 



