GROUPS OF GLASS MICROELECTRODES 



be used : however, if the study is to be made at a depth within it is usually 

 necessary to arrange the electrodes with their longitudinal axes parallel 

 so that they may be introduced in this direction. Tomita and Torihaina^^ 

 have described an arrangement for two electrodes in which one is actually 

 introduced through the other and both can be moved independently along 

 their common axis. 



A group of electrodes can be placed close together and parallel by using 

 their stems to ahgn them side by side. For this purpose the stem diameter 

 must be made equal to the spacing required, and the shanks and tips have 



Longitudinal 

 alignment 



(a) 



Transverse 

 alignment 



(b) 



Figure 35.16 Schematic representation of the alignment of electrodes 



to be coaxial with the stem. Such electrodes can only be prepared by 

 mechanical means. Inter-electrode spacing larger than the diameter is 

 accomplished by interposing a spacer such as paper, foil or cover slip. 

 With small spacing it becomes more difficult to make glass electrode 

 assemblies with parallel stemmed electrodes less than 0-1 mm diameter: 

 metal electrodes made of uniform wire may be of use. 



Groups of electrodes with very small spacing can however be arranged 

 by manipulating electrodes or their tips into place. For this purpose 

 capillary electrodes are drawn by hand with a range of tapers and lengths, 

 and the shanks of those suitable are cut off at the shoulder of the stem. 

 The open end forms a small funnel which facilitates the introduction of 

 wire connections. 



Longitudinal spacing — When a series of collinear points at different depths 

 are to be studied it is sometimes possible to introduce an electrode assembly 

 along the line. In this case the electrodes can be held together with their 

 tips placed at the required intervals along their shanks {Figure 35.16a). 

 This form of spacing is simpler to arrange than that side by side {Figure 

 35.16b). One electrode is cemented lightly with wax across a thick hypo- 

 dermic needle {Figure 35.19) with the aid of a small soldering iron. Some 

 Vaseline is applied to a small area of another electrode a short distance 

 from the thick end and the second electrode is placed along the first one. 

 The second electrode is manipulated under a microscope until the tip is at 

 the required position, the Vaseline being sufficient to support it in place 

 while they are cemented together. The cement used should be very thin and 

 spread by surface tension, but should not dry too rapidly. Durofix diluted 

 with ethyl alcohol has been found satisfactory but it tends to cover electrode 

 tips. A weak solution of gelatin can be used and is much less likely to block 

 the orifice; it can be dried quickly under a lamp and eventually hardened 

 if necessary in formalin. Further electrodes can be added in this manner. 

 Groups of seven electrodes at a spacing of 100-150 // have been constructed 

 which are not much larger near the tip than some single electrodes. 



563 



