13 



below the surface of the fluid suck up carefully to the 

 mark 101. 



6. Rotate thoroughly between finger and thumb 

 for some minutes. 



7.' Blow out the stem contents which are only 

 diluting fluid and then rapidly put a small drop on the 

 centre of the disc. 



8. Breathe on the cover glass and lower it rapidly 

 into position with a needle, so as to avoid bubbles. 



The fluid must cover the disc completely, and there 

 should be no air bubbles. If not filled properly, rotate 

 the pipette thoroughly before trying a second drop. 



9. When Newton's rings (i.e., the play of colours 

 seen on a film of tar, etc.) are seen between cover glass 

 and slide, then, and not till then, is the former in its 

 correct position and counting can be proceeded with. 



10. Make certain that the lines of the squares can 

 be focussed with the lens used, e.g. T Leitz. Generally 

 it is necessary to use the thin cover glass supplied and 

 not the thick one. Take care that the diaphragm of the 

 microscope is as nearly closed as possible. 



11. Examine with ai-inch lens to see that the red 

 cells are evenly distributed over the squares. If this is 

 not so the count is not reliable, and errors in mixing or 

 in filling the chamber have probably arisen. 



12. In case of red cells overlapping the sides of a 

 square, even in the slightest degree, count only those 

 on two adjoining sides. 



13. Count a thousand red cells. 



To COUNT THE WHITE CELLS 



The Pipette for Leucocytes. Has a stem of fairly 

 wide calibre. Above the bulb is the mark II. The 



