Abstract
Several types of microelectrodes have already been devised by different investigators. 1 In all these electrodes the conducting medium, whether of metal or of KCl-agar, is enclosed in a micropipette of glass or quartz. It is possible to make electrodes of similar fineness from metallic wires, but they are too flexible for use.
In the new type of microelectrodes described here, 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 micro-needles. The advantages are: (1) they can be easily made and in large numbers at one time, (2) many pure metals can be used, (3) electric contacts of any geometrical shape and fineness can be easily made, (4) the non-polarizable electrode can be made sterile, and (5) their electric resistance is low.
The best way to deposit films of metal on glass and quartz is by spattering, i. e., by placing them in the dark space of high voltage vacuum discharge. But for the deposit of silver films on glass needles, Brashear's 2 method of silvering glass has been found very satisfactory; for bright platinum films Meillere's method 3 is used.
The desired number of micro-needles is drawn in the way described in detail by Chambers. 4 The shank ends of the needles are warmed in a nicroflame and embedded vertically up in a block of paraffin and are then cleaned by immersing the needles vertically down in a beaker of cleaning fluid. After a few hours in the cleaning fluid the needles are thoroughly washed in running water and then kept immersed in a large beaker of distilled water till they are to be placed in the silvering solution.
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