II 
To Count the Red Cells 
The Thoma-Zeiss Pipette *—For counting the red 
cells has a narrower calibre than that used for 
counting white cells and the top of the bulb is marked 
ioi. The stem is equal to one part, consequently the 
bulb is equal to one hundred parts, and when one part 
of blood and diluting fluid fill the bulb, the dilution of 
the former one part is one hundred times. The glass 
ball in the bulb is simply to aid the mixing process. 
Diluting Fluid .—Blood cannot be counted without 
dilution as it is too * 1 2 3 4 thick. 5 6 In an emergency 0’9 per 
cent, salt solution may be used but preferably Hayem’s 
fluid, viz. :— 
Mercuric chloride I part 
Sodium chloride 2 parts 
Sodium sulphate 10 ,, 
Water 400 ,, 
Counting Chamber .-—The central disc has a number 
of minute squares (400) ruled upon it. The side of 
each smallest square is Fs mm. Therefore, the area of 
each square is ±ho mm. 2 , as marked on the slide. 
Further, when the cover glass is in position the depth 
* To Clean Pipettes 
For any accuracy of observation the pipettes should be scrupulously clean. 
There should not be the slightest tendency for the glass ball to stick to the sides. 
After a count has been made, the rubber tube is removed and the contents 
ejected by blowing from the pointed end. 
1. Suck up dilute acetic acid so that all traces of stain are removed. 
2. Suck up several lots of clean water to remove the acid. 
3. Then absolute alcohol two to three times to remove the water. 
4. Then ether two to three times to remove the alcohol. 
5. Finally, blow hot air through with a syringe, the glass barrel of which may 
be heated in a flame (or simply suck air through). 
6. Occasionally it is necessary to clean the bulb by digestion. The pepsin or 
trypsin can be got in tabloid form. 
