Chap. VI.] 



ELECTRODES. 



61 



Fig. 34. Platinum Electrodes. 



plate e, fixed into a block of vulcanite h. Through holes 

 in the vulcanite pass platinum wires, the ends of which 

 are beaten out flat and L-shaped. At the end d of 

 the platinum wires are 

 binding screws, by means 

 of which short wires from 

 the screws on b can be 

 attached, and these again 

 can be connected with 

 wires from an element or 

 induction coil. If then a 

 nerve be laid across the 

 L-shaped points, which 

 are not allowed to touch 

 one another, the current 

 will reach the nerve by 

 one platinum electrode, travel along the nerve till the 

 other electrode is gained, and so return. By the 

 screws in h the distance between one electrode and 

 another can be increased or diminished, and thus the 

 current can be made to travel through a greater or less 

 length of nerve. An easy way of making electrodes 

 suitable for physiological work is to pass two plati- 

 num wires through a piece of cork at the desired 

 distance from one another. The cork may then be 

 fixed to a support. The wires from battery or coil 

 can then be easily attached to two of the free ends. 

 Electrodes may also be made by fastening two wires 

 on either side of a slip of wood of the thickness suffi- 

 cient to keep them the desired distance apart. Coat 

 the whole with paraffin, and when it is cool the paraffin 

 can be scraped away and the requisite length of wires 

 exposed. 



The moist stimulation tube is devised to 

 meet an objection brought against other electrodes ; 

 the objection, namely, that a nerve laid over the 

 ordinary electrodes rapidly dries, and is, therefore^ 



