APPARATUS AND MANIPULATIONS 19? 



pended lamp equipped with a 150 watt bulb and Daylight glass 

 filter are also needed. 



2. Manipulations 



1. Connect a length of capillary tubing to the water manipulator, 

 and fix the tube on the stage of the microscope so that it is parallel 

 to, and lying on, the micrometer scale with its open end near the 

 edge of the optical field farthest from the manipulator. 



2. Force water from the manipulator into the tube until half of 

 its length is filled. 



3. Bring the tip of a pipette filled with the solution into the 

 optical field and insert it into the open end of the capillary tube. 

 Carefully blow the liquid out of the pipette, at the same time draw- 

 ing it into the tube by turning the piston screw of the water manipu- 

 lator. The volume of liquid introduced is determined by the length 

 of the column as measured on the micrometer scale visible through 

 the tube. When the appropriate amount of the solution has been 

 introduced move the column inward so that its distal meniscus is 

 near the center of the field. 



4. In the same manner introduce columns of reagents, and, when 

 these have been added, break off the portion of the tube containing 

 all the columns (about 3-4 cm. long) and seal both ends quickly in 

 a minute gas flame. Set aside in a horizontal position. When breaking 

 off the tube, caution is required to avoid including any portion of 

 the tube which has been wetted with the manipulator water ( a dia- 

 mond point is useful for cutting the tubes at the proper place) and 

 when the ends are sealed, care must be exercised to avoid heating 

 adjacent liquid columns. 



5. In order to mix the solutions, briefly centrifuge the sealed 

 tubes to bring the separated columns together, invert, and again 

 centrifuge. Then repeat the inversion and centrifugation. (This may 

 be simplified, see page 178.) 



6. When it is necessary to heat the mixture, place the tubes in 

 a hot water bath. 



7. Since it is essential that color comparisons be made with tubes 

 of the same diameter, the tubes to be compared should be obtained 

 from the same original length of uniform-bore tubing. When many 

 tubes are to be compared, the various original lengths of tubing re- 

 quired may not have the same diameters. In this case break a single 



