i6 



The standards fade in the tropics and must be 

 returned for graduation. 



Procedure. I. Place a little water in the gradu- 

 ated tube. 



2. Fill the pipette carefully, holding it almost 

 horizontal, and wipe off any blood on the outside. 



3. Blow out into the tube. Now wash out the 

 pipette thoroughly by sucking up and blowing out 

 successive lots of water from the rubber pipette supplied. 



4. Add water by successive amounts of five 

 scale divisions and stir thoroughly with a piece of wire 

 or probe. 



Sabli. Is constructed on the same principle as the 

 Gowers, except that in this case the standard is one of 

 acid haematin. The blood to be examined must 

 therefore be treated with about ten times its volume of 

 one-third per cent, hydrochloric acid ; then fill up with 

 water. 



It is a very accurate instrument. Gently shake 

 the standard when a sediment occurs. 



Fleischl-Miescher. Fully described in the book 

 accompanying each instrument. It is very accurate 

 but expensive. 



For choice use a Talqvist and Sahli. 



COLOUR INDEX 



When the haemoglobin [is 100 per cent, and the 

 red cells five million (i.e., with the ratio - p k ) 



k, OOO,OOO Jtx.D.C/ 



the colour index is said to be I. 



If this ratio were equal to I the colour index 

 would then be 50,000. So that to find the colour 

 index, after counting the red cells and estimating the 



