THE OPSONIC INDEX 217 



leucocytes) is pipetted off into a small tube, and the whole 

 is thoroughly mixed by repeatedly sucking into, and 

 expelling from, the pipette. The result is a suspension of 

 living leucocytes mixed with red corpuscles. 



The process.- (1) Make a pipette and place an india- 

 rubber teat on the thick end. With a grease pencil or 

 with ink, make a transverse line about an inch from the 

 point ; the volume of fluid contained between the point 

 and this mark is spoken of as the unit. 



(2) Having the patient's serum and the suspensions of 

 leucocytes and of bacteria ready to hand, take the pipette 

 between the index ringer and thumb of the right hand 

 and compress the nipple. Immerse the point beneath 

 the surface of the suspension of bacilli, and relax the 

 pressure on the nipple until the suspension has risen exactly 

 to the mark so that one unit has been drawn up ; then 

 remove the point from the fluid and relax the pressure 

 again so that a small volume of air is sucked up. This 

 will be quite easy if the point is a good one, otherwise 

 it will be difficult or impossible, as the column of fluid 

 will either refuse to stir or will oscillate violently. Next 

 immerse the point in the suspension of leucocytes and draw 

 up one unit. This will be separated from the suspension 

 of bacteria by the bubble of air. Kemove the point from 

 the suspension and draw up a second volume of air. 



Lastly, draw up one unit of the serum. There will now 

 be in the pipette (counting from the nipple towards the 

 point) one unit of bacterial suspension, a bubble of air, a 

 unit of leucocytes, a bubble of air, and lastly a unit of 

 serum (c, Fig. 35). 



(3) Put the point of the pipette on to a clean hollow- 

 ground slide or an artist's porcelain sunk palette, and 

 express the whole of its contents, and mix well together, 

 aspirating them repeatedly into the pipette and expelling 

 without causing bubbles. If bubbles form, a hot wire 



