25 



D. GELFAN. 



Another type of non-polarizable electrode has been designed by Gelfan. It 

 consists of three parts, the micropipette (Fig. 19, b), the tip of which 

 penetrates into the cell; the main pipette (Fig. 19, a), into the shank of 

 which the micropipette is sealed, and the AgCl electrode (Fig. 19, e). The 

 latter is sealed into a glass plug (Fig. 19, c) which is ground to fit perfect- 

 ly the other end of the main pipette. The main pipette and the capillary micro- 

 pipette are both filled with the same agar which is impregnated with KC1. The 

 system is then Ag (Fig. 19, d), AgCl (Fig. 19, e), KC1 in agar (Fig. 19, f). 



b 



Fi* 19 



The main pipette (Fig. 19, a) is drawn out from glass tubing to a suitable size 

 for the pipette-holder of the micromanipulator. For the micropipettes, capillary 

 pipettes are drawn out from clear quartz tubing to about 0.5 mm. in diameter. 

 These in turn are drawn out at one end to minute points over an oxygen micro- 

 flame. The tips of the pipettes, which have openings of about 1-2 microns in 

 diameter, are bent at an angle of almost 90 degrees. 



The author further discusses the preparation of the AgCl electrode, the prepar- 

 ation of the agar, and describes the method of filling the micropipette with agar. 



The electrodes when used are connected in series with ^two or three dry cells, 

 a two-way switch, and a sensitive Leeds and Northrup galvanometer. The wires of 

 the system must be well insulated. 



