26 PRACTICAL HISTOLOGY [ill 



1. With a cloth carefully remove any blood adhering to the 

 point of the pipette. Slowly draw up Hayem's fluid, gently 

 turning the pipette until the mixture is exactly at the mark 101. 

 Put the finger on the tip of the pipette, leaving the capillary tube 

 full of the diluting fluid, and by gently shaking thoroughly mix the 

 blood arid the fluid, taking care that the contents of the capillary 

 tube are not drawn up into the diluting chamber. The blood is 

 thereby diluted 1 in 100. Allow the contents of the capillary 

 tube, and a few drops of the diluted blood, to escape, and then at 

 once carefully place a small drop of blood on the centre of the 

 counting chamber. Put on the cover-slip by a sharp lateral 

 thrust ; this assures its close apposition to the wall of the 

 chamber and Newton's colour rings should appear. Allow two 

 or three minutes for the corpuscles to settle, then count the 

 number of corpuscles in at least 10 adjacent squares, including 

 in each square any corpuscles overlapping the upper and the left 

 boundary lines but, by way of compensation, excluding those 

 overlapping the lower and right boundary lines. 



In order to facilitate the process of counting the squares are 

 divided into groups by lines bisecting every fifth horizontal and 

 vertical column of squares. 



Determine the average number found for a square. Since 

 the fluid on each square is 33^ cub. mm. the average number 

 of corpuscles found multiplied by 4000 gives the number in 1 cub. 

 mm. of the diluted blood, and 100 times this is the number in 

 1 c.mm. of the blood. 



8. Enumeration of the white corpuscles. Dilute the blood 

 1 in 10 with the mixing pipette (7, Fig. 1, using the same 

 precautions as before, and taking care that a large drop of 

 blood is collected before the point of the pipette is put into 

 it. As diluting fluid use "5 p.c. acetic acid (coloured with methyl- 

 violet) since this renders the red corpuscles invisible. Count the 

 number of white corpuscles lying on the large squares formed 

 by the lines bisecting every fifth horizontal and vertical column 

 of small squares. Count the number on ten of these large 

 squares, using a rather low power unless the microscope is fitted 

 with a mechanical stage. Calculate the average number for a 



