Estimation of the red corpuscles 183 



the best, although gentian violet will do very well. This colours 

 the leucocytes, so that they are readily distinguished from the red 

 corpuscles.* 



4. A microscope having a |-inch lens which will focus through 

 the thick cover-glass suppHed with the hsemocytometer. If the 

 examination is not to be made by the bedside, a strong indiarubber 

 band a little shorter than the pipette should be carried. 



Process. 



I. 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 prepara- 

 tion of films by the cover-glass method ; an additional advantage 

 is that the patient can put his hand into the position most con- 

 venient to you, and you have not to lean over him. 



The area of the skin to be punctured may be washed with soap 

 and water and then with pure water, and wiped dry, but this is 

 not really necessary. It is necessary, however, to rub the patient's 

 ear or finger well with a towel or piece of lint, so as to make it 

 hypereemic ; unless you do this you may have difficulty in 

 collecting sufficient blood, especially if the skin is cold. The 

 needle is sterilized by being passed slowly through the flame of a 

 spirit-lamp or Bunsen 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 with- 

 drawn for this examination ; the blood must always be allowed 

 to flow out naturally, but if a flat needle be used, the edges of the 

 cut made by it may be held apart by gentle pressure with the 

 finger and thumb. 



* The following formula is better : Distilled water, i6o c.c. ; glycerin, 

 30 c.c. ; sodium sulphate, 8 grammes ; sodium chloride, i gramme ; methyl 

 violet, a trace (Toison's fluid). 



