CAPILLARY DIVER TECHNIQUE 389 



pipette and diver less important than it is when microliter divers 

 are used. 



The ball-tipped pipette may also be used to place oil in direct 

 contact with W, if desired. This is accomplished by moving the ball 

 very close to W so that the oil will be able to come into contact 

 with W before a separate seal can be formed. The thickness of such 

 an oil layer can be regulated by drawing back into the pipette any 

 excess oil. 



Placing Mo. A glass tube is fitted on the rubber stopper (r) to 

 form a vessel around the diver as in C, Figure 135. The vessel is 

 filled with flotation medium to 2-3 mm. over the top of the diver. 

 In order to facilitate observation under the microscope, a square 

 piece of cover slip is cemented on the tube with Canada balsam and 

 the edges of the cover slip are held with DeKhotinsky cement to 

 prevent it from sliding off {E, Fig. 135). 



M2 is then placed by withdrawing air from the end of the diver 

 through the tip of a pipette, arranged as shown in E, Figure 135. 

 As the tip is brought into the end of the diver, gentle suction is 

 applied so that the end of the tip is kept at the surface of the 

 medium. In this way, the length of Mo will be equal to the distance 

 the end of the pipette tip is brought into the diver. 



Zeuthen (1943, page 506) has described the process of placing a 

 1.00 mm. M2 as follows: 



"Before the pipette is introduced into the diver, a horizontal Une in the ocular 

 01 the micro.scope is brought to intersect with the image of the pipette 1.00 mm. 

 from its tip ; in placing il/n, the diver, encircling the pipette, is raised so much 

 that its edge is just level with the line chosen in the ocular. After making sure 

 that actually a current of medium has passed from the surrounding liquid 

 through the diver's neck into the pipette, the latter may be withdrawn from 

 the diver, emptied by blowing, and rinsed with water." 



Placing Ml. The medium in the vessel surrounding the diver is 

 poured out; the diver is inverted and the M2 end is placed in the 

 slit. The vessel is again filled with medium, and the ensuing pro- 

 cedure is the same as that used for placing M2. 



Transfer of Diver to Flotation Vessel. 



1. Remove diver from the slit and allow to float in the medium 

 over the rubber stopper with the M2 end upward. 



2. Draw the diver up into an ordinary pipette having a drawn- 

 out tip, along with about 0.5 ml. medium. Keep the ilfo end up. 



