The Washed Leukpcytes 



283 



by a rubber bulb. The object of the experimenter is to take up 

 into this pipette , equal quantities of the creamy layer of blood- 

 corpuscles, of 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 bacterial suspension to the same point, withdraws the tube, 

 and permits 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 repeatedly 

 expelling them upon a clean glass slide, and redrawing them into the 



Fig. g6. — Mixing liquids by repeatedly expelling on to slide and redrawing 

 into pipette (Miller). 



tube. After thus being thoroughly mixed, the fluid is once more 

 permitted to enter the capillary tube and come to rest 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 temperature 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 sedi- 

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

 escape upon a perfectly clean glass sUde 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 shde is 



