124 



METHODS OF EXAMINING SERUM 



blood should be obtained. The diluted blood is then centri- 

 f ugalised, and when the corpuscles are separated the supernatant 

 fluid is removed, '85 per cent, saline is substituted, and the 

 centrifugalisation repeated. The fluid is again removed, care 

 being taken not to disturb the layer of white cells lying on the 

 top of the red corpuscles. This layer is then pipetted off into 

 a watch-glass or tube, and the leucocytes required are thus 

 obtained. 



(3) Preparation of the' Sera. The serum whose sensitising 

 effect on the bacteria it is desired to test is obtained by Wright 

 as follows : A " blood-capsule " is made by drawing a piece of 

 No. 3 quill tubing into the shape shown in Fig. 45, the part not 

 drawn out being about 1 inch in length. It is convenient to 

 make a number of these capsules at 

 one time, and to draw off their 

 extremities and seal them in the 

 flame. For use, the tips of both 

 extremities are broken off, the finger 

 is pricked, and blood allowed to pass 

 into the capsule through the bent 

 limb till the capsule is about half 

 full. The air remaining in the 

 capsule is rarefied by passing the 

 straight end through a flame and 

 then sealing it off. By this manipul- 



FIG. 45. -Wright's blood-cap- ation the blood is sucked over the 

 sule, and method of filling bend into the straight part of the 

 same, tube, and the bent end is now also 



sealed off or closed with wax. It is 



well to shake the blood down towards the closed straight end, 

 care being taken to previously allow the glass to cool sufficiently. 

 The capsule is now hung by the bend on the edge of a centri- 

 fuge tube, and the serum separated by spinning the instrument. 

 In any particular case a capsule of serum from the infected 

 person and one from a normal individual are prepared. 



The emulsion, corpuscles, and serum being thus prepared, 

 the next step is to mix them. This is done by taking a piece 

 of quill tubing and drawing it out to a capillary point so as to 

 make a pipette about 8 inches long; on the thick end of 

 this a rubber teat is fixed, and about 1 inch from the capillary 

 point a mark is made with an oil pencil. From the watch-glass 

 containing the separated leucocytes a portion is sucked up to 

 the mark, and then an air-bubble is allowed to pass in. A 

 similar portion of the serum is drawn up, and then another 



