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 

 101. 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 c thick.' 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 A mm. Therefore, the area of 

 each square is iro 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. 



