PREPARATION OF THE SERA 



125 



practised, the supernatant fluid removed, and the red and white 

 cells uniformly mixed. 



(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 manipulation 

 the blood is sucked over the bend 

 into the straight part of the 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 

 centrifuge tube, and the serum sepa- 

 rated by spinning the instrument. 



In any particular case a capsule of 



r ,1 ,. , n T FIG. 45. Wright s blood-cap- 



serum from the infected person and sulej and m | thod of fillh f g 



one from a normal individual are same. 

 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. A portion of washed 

 corpuscles 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 air-bubble, and finally a similar portion of 

 the bacterial emulsion. The three droplets are carefully blown 

 on to a slide, and are thoroughly mixed with one another by 

 being alternately drawn up into the tube and expelled ten times. 

 The mixture is then drawn into the tube, and the end sealed off 

 in the flame. The rubber nipple is . removed, and the tube 

 placed in the incubator at 37 for fifteen minutes. A slide is 



