12 



of fluid lying over the squares is TS mm. (= 0*1 as 

 marked on the slide). Therefore, the volume of fluid 

 lying over each square is 4tjo x A = ioVo mmA 

 Suppose, now, that on counting we find ten red cells on 

 a square. Then in T^OO mm. 3 there are ten red cells. 

 Therefore in I mm 8 , there are 10 x 4000 = 40,000 red 

 cells. But the blood has been diluted 100 times. 

 Therefore, normally, there would be 40,000 x 100 = 

 4,000,000 in I mm*. 



In practice it is not sufficient to count one square 

 but it is necessary to count many. If then we add up 

 all the red cells (e.g. 1000) counted and divide by the 

 number of squares counted, we get the number for one 

 square. So that we get this formula for the number of 

 corpuscles per mm. 3 



4000 x dilution x total number of red cells counted 

 Number of squares counted. 



The normal average values are for man 5,000,000 

 and for woman 4,500,000. 



Orientation Lines. Every fifth row of squares has 

 a line drawn through its middle dividing it into two 

 oblongs. These lines are simply 'to prevent the eye 

 losing itself among so many small squares, and for 

 purposes of counting or calculation are disregarded. 



Procedure. I. The pipette must be quite dry 

 and the glass ball move quite freely. 



2. Prick the finger ; the blood must flow freely. 

 Pressure on the finger must not be used as plasma is 

 squeezed out of the tissues. 



3. Place the tube in the mouth and hold the 

 pipette so that the scale is completely in view. 



4. Suck up blood exactly half-way, i.e.^ 0*5 for 

 bloods fairly normal, but to I for anaemic bloods. 



5. Wipe off adherent blood, and placing the point 



