GLASS MICROCAPILLARY ELECTRODES 



the block on a flat surface. Essentially this arrangement merely serves to 

 steady the hand. Although with the dissecting microscope the actual tip 

 cannot be observed, this method is capable of giving good results with 

 practice. With the multi-stage method the shape of each part of the electrode 

 can be controlled, a considerable advantage for some experiments. 



Other instruments for the production of microelectrodes utilizing 

 gravitational force have been constructed in which the capillary is drawn 

 horizontally in one stage (Kao^^). On the whole it seems that if an elaborate 

 construction is undertaken a flexible method of providing power should 

 be employed. 



Machines operated by springs — Many types of elastically operated micro- 

 electrode pulling machines have been constructed, though few have been 

 featured in publications. Three types are described here. 



Glass tubing 



Elastic, 



Stationary 



■X' block 

 with clamp 



Sliding "X" block 

 with clamp 



Elastic 

 Supporting rod 



Figure 35.1 A simple microcapillary pulling device 

 from a description by Crain^* 



The simplest mechanism is that in which one of a pair of clamps is mounted 

 on a horizontal slide operated by a spring or elastic band (Crain^*). Once 

 the glass tube is clamped, the elastic is stretched to the required degree and 

 heat applied either with a gas jet or electrically heated coil. An effective 

 sliding arrangement can be made from an X block and a metal rod, with 

 two elastic bands, one on either side of the rod (Figure 35.1). Various 

 additional features may be provided such as a knock-down switch to cut 

 off" heating current, and a mechanical switch to bring in additional elastic 

 bands. 



A more intricate type of spring operated machine is shown diagramma- 

 tically in Figure 35.2. The action of this machine is similar to manual 

 drawing. The glass tube is pulled apart and is simultaneously lifted away 

 from the heating loop. Two toothed discs 7 in. diameter are engaged side by 

 side, with rotatable clamps for glass tubing mounted near the periphery. 

 A horizontal rod sliding through both clamps keeps them parallel at all 

 positions, and heat is applied by an open U shaped loop of nichrome wire. 

 The machine is operated by a vertically mounted coiled spring attached to 

 a string which is wound round a grooved wheel mounted coaxially on one 

 of the large toothed discs. The spring acts to unwind the string by rotating 

 the discs, thus pulling the clamps apart. The pulling force can be varied 

 by altering the length of the spring. 



538 



