22 



capillary arei contamination, non-uniform filling with agar, air bubbles 

 inequalities in the electrolyte concentration of the agar. 



B. TAYLOR (MICROELECTEODES AND MI3ROMAGNETS) 



Two kinds of microelectrodes and one micromagnet have been perfected and used 

 with very good results. First, it was found that a platinum wire ( No. 35, G.P.) 

 inserted into a close-fitting quartz capillary can be drawn over a minute' oxy-' 

 acetylene flame to a perfectly insulated needle-point less than one micron in 

 diameter. Indeed, the platinum core in this exceedingly fine point may closely 

 approximate the limits of microscopic vision. 



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 3 

 4 



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The platinum wire at the opposite (undrawn) end extends a few mm beyond the quarts 

 capillary in order that the former may be annealed to an insulated copper wire of 

 about the same diameter as that of the platinum wire and two feet in length. The 

 drawing of the electrodes (see Pig. 17, 1 and 2) and the annealing are readily 

 done over the oxy-acetylene microburner (m.b.). About 3 mm. of the needle-tip of 

 the electrode is bent over the flame, at right angles (Pig. 17, 3, sh). This shank 

 fits into the instrument-holder of a micromanipulator. By means of the latter the 

 electrodes are operated with finest precision in a moist chamber on the stage of 

 the microscope. 



The second type of microelectrode is non-polarizable. For many purposes the platinum 

 electrode would appear to be entirely satisfactory, but certain experiments make 

 necessary the use of this second type. 



A micropipette, made preferably from a quartz capillary of about 1 mm in outside 

 diameter and 50 cm long, is filled by means of a good Luer syringe with a melted 

 0.5 per cent KCI solution of carefully dialyzed agar. When the agar solution has 

 thoroughly hardened, the micropipette is sealed with White's dental cement (of low 

 melting point) into a glass shank (Fig. 17, sh. ) similar to that described above 

 for platinum electrodes. The inner end of the pipette, which should extend only a 

 few mm into the "bowl" of the shank, is now well covered with a few drops of the 

 melted agar solution. When the agar has thoroughly cooled, the bowl of the shank 



