256 THE BLOOD. [CH. X. 



of blood has collected the pipette is placed in this and very gentle 

 suction applied, the pipette being held nearly horizontal, and care 

 being taken to avoid the introduction of an air bubble. If the blood 

 does not reach the mark, the finger is firmly pressed again, and the 

 blood drawn slightly above the mark. The exterior of the pipette 

 is wiped with a piece of filter paper, the blood run on this to the mark 

 and then discharged on to the piece of absorbing paper, the pipette 

 being completely blown out at the end of the operation. 



With a little practice the whole process is rapidly completed, and 

 there is little risk of the blood clotting. As soon as the pipette has 

 been drained a little dilute alkali should be sucked up and blown 

 out two or three times, to prevent the film of blood clotting in the 

 pipette. This is then thoroughly washed with distilled water, 

 alcohol and then with ether. It can be dried by attaching it to a 

 suction pump. 



2. Drying the paper. After standing for a few minutes the 

 paper is held in a little clip and suspended in the steam oven at 

 100 C. for 3 to 4 minutes. 



3. Coagulation of the proteins. Place the paper, without the 

 clip, in a clean, dry, rather wide test-tube of such a size that the 

 paper is completely immersed by the 6J cc. of solution. Measure 

 6J cc. of the acid solution of potassium chloride into another test- 

 tube. Boil and rapidly pour the vigorously boiling solution on to 

 the paper in the other tube. Allow the tube to stand for at least 

 30 minutes. Transfer the fluid to the 50 cc. flask. Wash the paper 

 with another 6J cc. of cold acid potassium chloride, and add this to 

 the fluid in the flask. 



4. Method of heating the solution. To the flask add i cc. of 

 the copper solution and fit the rubber sleeve on to the neck. Place 

 the screw clip over the rubber, but do not tighten it. Have the 

 heating apparatus ready and properly adjusted. Place the flask 

 on the centre of the heated gauze and note the time. The solution 

 should commence to boil in i| minutes. Allow the solution to boil 

 for exactly 2 minutes. Just before the two minutes is completed, 

 commence to tighten the screw clip C. When the time has expired 

 tighten the clip very firmly, remove the flask at once and plunge it 



