APPENDIX II 409 



the measurement that is, to see that the jelly will actually excite 

 living cells by placing a drop of fresh citrated blood on to another 

 part of the same film and noting whether stimulated movements of 

 all the leucocytes occur. 



Procedure for the preparation of capillary tubes containing the 

 plasma of one person and the leucocytes of another. It will simplify 

 description if the details of sterilisation and the precautions for 

 ensuring asepsis are omitted. Since the presence of bacteria 

 shortens the lives of leucocytes (2) it is obvious that aseptic pre- 

 cautions are essential, but the details for sterilisation are so well 

 known that they need hardly be repeated. A capillary tube of 

 glass is prepared which has such a diameter that blood will run 

 into it by capillarity and at the same time its flow can be controlled 

 by gravity. I use a tube with a lumen of about two millimetres. 

 15 portions equal to each other are marked off with a pencil. The 

 marks begin at one end of the tube which is zero, but the tube 

 is at least two inches longer than mark 15. The portions are 

 rendered equal by calibration with mercury, and although the 

 length of each is immaterial, I have found that about half a centi- 

 metre is a convenient length for practical purposes and I use a tube 

 about 13 centimeters long. A neutral solution is made which 

 contains 3 per cent of sodium citrate and 1 per cent of sodium 

 chloride. Some of this is drawn up into the .tube until its upper 

 limit or meniscus stands at mark 6. Blood from the finger of the 

 person whose plasma is going to be tested is added until the 

 meniscus stands at mark 12, care being taken that no bubble of 

 air separates the two fluids. Mixture is carried out by allowing 

 the two fluids to gravitate up and down the tube six times. The 

 tube is sealed and centrif ugalised ; the blood being driven towards 

 zero. The end remote from zero is then unsealed and the portion 

 containing the precipitated corpuscles is separated and discarded 

 by cutting the tube at 4. Eight portions of the tube now contain 

 citrated plasma. If, owing to the sealing process, much of the tube 

 has been occluded at zero the upper meniscus may stand above 

 mark 12. This can be corrected by tapping out the excess of fluid 

 on to a sterile slide, controlling the amount removed by the finger on 



