A New Micro-Electrode for Electro-physiological Work

Abstract

AN electrode suitable for picking up single-fibre potentials from mammalian nerves should have the following characteristics: (a) a low electrical impedance to reduce the pick-up of ‘noise’, (b) a small diameter to isolate single fibres, and (c) sufficient rigidity to prevent it from bending or breaking when inserted into the nerve. The use of electrolytic conductors is unsatisfactory from the point of view of (a) and (b). The use of a thin wire the end of which protrudes from an insulating glass capillary suggests itself for overcoming these difficulties. There is no question of feeding the wire into the capillary portion of the tube from the wide end. Therefore, the reverse procedure was adopted. Capillary tubes were drawn out by a method previously described¹. A piece of silver wire (diameter, 0.61 mm.) was soldered to a piece of platinum wire of similar diameter. The silver wire was previously drawn out and annealed in turn until it broke with a blunt point, thus allowing one to push it farther into the capillary part of the tube than would otherwise be possible. Grinding the wire to a sharp point involves a greater risk of breaking the capillary. The wide part of the tube was sealed to the platinum, care being taken lest the solder joint was melted.