13 
below the surface of the fluid suck up carefully to the 
mark ioi. 
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 . 9 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. y 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 Pifette for Leucocytes .—Has a stem of fairly 
wide calibre. Above the bulb is the mark 11. The 
