26 



E. SEN. 



In the type of electrode devised by Sen, the conducting medium is a continuous 

 film of silver, gold, or platinum for stimulating electrodes; and silver-silver 

 chloride for non-polarizable electrodes, on the outer surface of glass or quartz 

 microneedles. Any desired number of microneedles is drawn out according to the 

 method of Chambers, the shank ends of the needles are warmed in a micro-flame 

 and embedded vertically in a block of paraffin. The needles are then cleaned by 

 immersing vertically down in a beaker of cleaning fluid for some hours, and then 

 thoroughly washing them in running water. They are then silvered by Brashear's 

 method, washed and dried in a hot oven. Electric contacts with these silvered 

 needles are made by inserting them in the electrode holder (Pig. 20, g /'lass 

 tube, W, '.Vood's metal, E, microelectrode, L, copper wire lead). 





w 



Pig.Z0 



food's Metal previously placed in the tapering end of the holder, is melted by 

 gentle heat and the needle thrust in. On cooling of the metal a good contact is 

 secured. After mounting the coated needle in this way, thicker coats of silver 

 or any other metal can be deposited electrolytically. The electrodes are washed 

 and kept in distilled water for some hours before use. 'Then necessary the metallic 

 film of the shank can be insulated by applying shellac with a fine brush. The 

 insulation of the micro-tip is done under a microscope. The tip pointed upward 

 is illuminated in the dark field of the microscope and its shank is gradually 

 lowered by rack and pinion into a small cup of shellac solution. By this method 

 one can insulate to within 5-10 microns from the tip. Ettisch and Peterfi, 1925a, 

 b, Gelfan, 1927, Taylor, 1925 a, Taylor and V/hi taker 1926, '27, '•right and 

 McCoy 1927. 



