The Washed Leukocytes 



275 



the blood-serum, and of the bacterial suspension. Wright first 

 makes a mark with a wax pencil about i centimeter from the end 

 of the capillary tube. He first draws up the leukocytic layer of 

 blood-corpuscles to this mark, then removing the tube, permits the 

 column to ascend a short distance. Next he draws up the bac- 

 terial suspension to the same point, withdraws the tube, and per- 

 mits the column to ascend; then draws up the serum to be taken 

 to the same point; thus in the same capillary tube he has three 

 equal volumes of three different fluids, separated by bubbles of 

 air. It is next necessary to mix these, which is done by repeat- 

 edly expelling them upon a clean glass slide, and redrawing 

 them into the tube. After thus being thoroughly mixed, the fluid 

 is once more permitted to enter the capillary tube and come to rest 



Fig. 100. — Mixing liquids by repeatedly expelling on to slide and redrawing 

 into pipette (Miller). 



there. The end is now sealed in a flame, the rubber bulb removed 

 and the tube placed in a thermostat, or in case much work of the 

 kind is being done, to an opsonizing incubator in which the tempera- 

 ture is not modified by opening and closing the doors. The tube 

 remains in the incubating apparatus at 37°C. for fifteen minutes 

 (some use twenty, some thirty, minutes as their standard), is then 

 removed, whirled about its long axis between the thumbs and fingers 

 a few times to mix the contents from which the corpuscles have 

 sedimented, its end is broken off, and a good-sized drop is allowed to 

 escape upon a perfectly clean glass slide and spread over its surface. 

 The spreading is a matter of some importance, as an even dis- 

 tribution of the leukocytes is desirable. The capillary tube from 

 which the drop has escaped will form a good spreader if laid flat 

 upon the glass and drawn along, but the edge of another slide is 

 better, and in distributing the fluid, it is better to push than to pull 

 it with the end of the slide, rather than its side. 



