23 



is almost filled with slightly moist, well pulverized AgCl (C.P.). Into the 

 silver chloride is inserted a No. 20 silver wire of convenient length (about 

 1 ft.). The end of the "bowl" is then filled and completely sealed with de 

 Khotinsky cement which thereby firmly holds in place the silver wire. It is 

 advisable to insulate the exposed portion of the silver wire by coating it 

 with de Khotinsky cement or by means of glass beads which can be quickly made 

 by cutting a capillary tube into lengths of 1 cm each. 



After mounting the two electrodes of this type in the micromanipulator they 

 are "shorted" for some time previous to use, in order to obviate any difference 

 of potential. 



The E.M.F. is provided by a dry cell of about 1.5 volts { the voltage being 

 precisely determined by means of a Weston Standard Cell ). Included in the 

 circuit are two resistance boxes totalling 12,000 ohms and one of 40 ohms, a 

 nitrogen-mercury key and a specially designed Leeds and Northrup galvanometer 

 having a sensitivity of 35,714 megohms. 



The micromagnets, consisting of quartz with a soft iron core, are drawn in 

 the same manner and quite as fine as the platinum electrodes described above. 

 Into a close-fitting quartz capillary 30 cm long is inserted a No. 30 soft 

 iron wire with free ends extending 20 cm beyond either end of the capillary 

 tube. The magnets are then drawn over the microburner as illustrated in Figure 

 17, 1. The very tip of the iron core is completely enclosed by the quartz. 

 After slightly curving the drawn ends ( Fig. 17, 5) each magnet is thereupon 

 mounted and temporarily cemented into the glass shank such that the free end of 

 the iron wire projects 3 or 4 cm beyond the base of the shank. This permits the 

 soldering of the wire onto one end of the soft iron core (i.e., Fig. 17,5) of 

 the magnet spool (m. s.). This spool, made of wood, is 2.5 cm long and 1.5 cm in 

 diameter - a size sufficient to accomodate the winding on of 1500 ft. of No. 36 

 triple insulated copper magnet wire (m.w. ). One end of the soft iron core (4 mm 

 in diameter) should extend about 3 mm beyond the spool in order to provide support 

 for the glass shank. Having soldered the iron wire to the projecting core, the 

 glass shank, now unsealed from the micromagnet, is slid over the free end of the 

 iron core whereon it is firmly cemented by means of the de Khotinsky wax. In turn, 

 the micromagnet is permanently cemented in the shank (Fig. 17, 5). 



The micromagnets, like the mieroelectrodes, are supported and operated in the moist 

 chamber by means of the micromanipulator. 



It is evident that these electrodes and magnets afford a means for the study of 

 , the electric and magnetic properties of protoplasm in the interior of a living cell, 

 thus eliminating an unknown factor - the cell-membrane. But they also provide 

 means for an independent study of this unknown factor. It is believed that other 

 uses also may be made of these microinstruments. 



0. TAYLOR AND WHITAKEH. 



A hydrogen microelectrode has been designed by Taylor and Whitaker. Gases or 

 liquids may be substituted in place of hydrogen for either the saturation or the 

 protection of the platinum electrode. The microelectrode is non-polarizable, and 

 is sheathed within a quartz micropipette. Its construction is as follows J 



A platinum wire is tightly fitted into' & quartz capillary and the two together are 

 drawn to microscopic dimensions over a minute oxygen-gas flame. The electrode tip 

 is then cut off under the microscope at a suitable point with a microdiamond. 



