ESTIMATION OF RED CORPUSCLES. 145 



PROCESS. 



1. Pricking the patient. The blood may be procured 

 from the convex border of the lobe of the ear or from 

 the lateral surface of the last phalanx of the finger. 

 The advantage of the former situation is that the pain 

 is very slight, the skin being thin, and that the patient 

 cannot see what you are doing and is not likely to start 

 at the critical moment. It is to be recommended for 

 children and nervous women. The advantage of the 

 finger is that the skin is free from hairs, and these are 

 objectionable in the preparation of film preparations by 

 the cover-glass method ; an additional advantage is that 

 the patient can put his hand into the position most 

 convenient to you and you have not to lean over him. 



The area of the skin to be punctured is washed 

 with soap and water and then with pure water, and 

 wiped dry. No other sterilisation is necessary unless 

 you are also taking blood for bacteriological purposes. 

 The needle is sterilised by being passed slowly through 

 the flame of a spirit lamp or Bunsen's burner ; the area 

 of skin to be pricked is taken between the finger and 

 thumb of the left hand, and a rapid and fairly deep stab 

 made with the needle. The skin is then released and a 

 drop of blood allowed to exude ; this is wiped away and 

 the next drop which oozes out is used for examination. 



The skin must never be pinched when blood is being 

 withdrawn ; the blood must always be allowed to flow 

 out naturally. 



2. Filling the pipette. The degree of dilution is deter- 

 mined by the number of corpuscles per cubic millimetre 

 which you expect to find. If the patient is anaemic use 



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