MICROLITER BIYER TECHNIQUE 369 



of the heated air, so it is necessary to remove it from the flame be- 

 fore the enlargement exceeds 10-15 fi. 



A stopper is placed in an oil seal by introducing it into the diver 

 with fine forceps and dropping it into the oil seal. A bubble, usually 

 found under the stopper, is removed and the stopper is completely 

 submerged at the same time by pushing the stopper down with the 

 tip of the oil pipette until the bubble bursts at the lower meniscus. 

 To remove a stopper from an oil seal, the mouth seal is first re- 

 moved, and the mouth of the diver is rinsed with water and dried 

 with filter paper rolls. Then the whole space over the oil seal is filled 

 with oil and the diver is inverted into oil to let the stopper fall out. 



A stopper is placed in the mouth seal by the following procedure: 



1. Place the fully charged diver in the flotation vessel where it 

 will remain at the surface because it has been calibrated to bear a 

 stopper and is therefore too light. 



2. Rinse the mouth seal with medium (page 367). 



3. Pick up the stopper with the forceps especially designed to 

 handle it (Fig. 129) and place the tip of the stopper which protrudes 

 from the forceps into the mouth of the diver. Linderstr0m-Lang 

 and Holter (1942) describe the forceps as follows: 



5 cm. 



Fig. 129. Forceps for placing glass stoppers. 

 From Holter (1943) 



"It consists of a piece of thin metal tube, 15 cm. long and 2-5 mm. outside 

 diameter, which encloses a metal pin, 1.5 mm in diameter, 2 cm. longer than 

 the tubing and ending in a knob. On its lower end the tube carries two narrow 

 sheets of springy metal, 2 mm. wide and 2 cm. long, which are soldered on to 

 the outside of the tube in such a fashion as to protrude 15. mm. over the mouth 

 of the tube, parallel to its axis. By a slight bend the sheets are made to meet 

 at their ends, thus forming a pair of tweezers. Between the knob at the upper 

 end of the pin and some kind of button near the upper end of the tube lies 

 a spring which, when at rest, keeps the pin partially lifted out of the tube. By 

 pressing the knob of the pin down one forces the tweezers apart, thus releasing 

 any object which they have held." 



