238 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



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 hyperaemic ; 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 edg*es 

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

 with the finger and thumb." 



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 i in 100; if 

 he has approximately the normal number of corpuscles, or if 

 you have reason to think that they are present in increased 

 quantities, use a dilution of I in 150 or i in 200. 



In most cases you will find it advisable to count the red 

 and the white corpuscles in the same specimen, and if this is 

 the case, use a dilution of i in 100, whether you expect the 

 patient to be anaemic or not. It is less easy to count the 

 reds (if numerous) with this low degree of dilution than with 

 a higher one, but it is not really difficult, and if you use a 

 higher degree of dilution considerable error will be intro- 

 duced into the leucocyte count. 



Having decided upon the degree of dilution, insert the tip 

 of the pipette into the drop of blood lying on the skin, take 

 the bone mouth-piece attached to the indiarubber tube in 

 your mouth, and suck the blood up to the appropriate mark. 

 If air-bubbles gain access, blow the blood out and begin again 

 quickly. If you overshoot the mark, remove some of the 

 blood by touching the tip of the pipette against some lint or 

 absorbent cotton-wool. Be careful, also, to wipe off any 

 blood there may be on the outside of the tip. Place the tip 

 of the pipette in the diluting fluid ; a small quantity should be 



