stem contains one part. The dilution of the fluid in the 

 bulb is therefore ten times (vide supra). The object is 

 to use blood as little diluted as possible, as leucocytes 

 are comparatively few in number. 



The Diluting Fluid. About one -half per cent, 

 acetic acid is used in order to dissolve the obscuring red 

 cells. To this is added a little filtered stain, so that the 

 nuclei of the leucocytes are coloured. 



The Counting Chamber. If we take the normal 

 value for leucocytes to be 10,000 per mm. 3 ; then, on 

 400 squares (i.e., the whole of the ruled area) there 



would be 10,000 x -3 = 1000. But the blood is 



4000 



diluted ten times so that 100 would be the possible 

 maximum. Now this number is too small to give an 

 accurate result, so that it is necessary to use a chamber 

 which has a set of extra squares ruled, e.g., Turk's 

 leucocyte counter. By the use of this it is theoretically 

 possible to count 900 leucocytes. 



Calculation. The number of leucocytes per mm. 3 

 4,000 x total number leucocytes counted x the dilution 

 Number of squares counted. 



The normal value for leucocytes is about 10,000. 



Procedure. I. Pour out the diluting fluid into a 

 watch glass. 



2. Suck up the blood, which must be plentiful, 

 to mark I, holding the pipette nearly horizontal, as 

 otherwise the blood will flow out. This tendency may 

 be checked by plugging the rubber tube with cotton- 

 wool. 



3. Wipe off blood from outside of the point. 



4. Place the_finger on the point and then place 

 the point below the surface of the diluting fluid. 



5. Now suck and, while still sucking, remove the 



