THE TECHNIQUE OF SERUM REACTIONS 267 



In the given case, 0.001 c.c. of the serum represents one unit, and 

 0.002 c.c., two units, is the quantity to be used for each test. 



III. The Complement. The complement used in Wassermann re- 

 action is fresh guinea-pig serum. This may be obtained in one of the 

 following ways : A guinea-pig may be killed by an incision in the throat 

 and the blood allowed to flow into a large Petri dish. This is set away 

 in the ice chest until clear beads of serum have formed upon the sur- 

 face, and these are then carefully removed with a pipette. 



It is more economical to puncture the heart of large guinea-pigs 

 with a needle attached to a syringe and withdraw 5 or 6 c.c. of blood 

 without killing the animal. This can be transferred to a centrifuge 

 tube and the serum obtained by centrifugation after clotting. Serum 

 used as complement in the Wassermann reaction must be titrated each 

 day before reactions are done. This is, done by putting into a series of 

 tubes 1.0 c.c. (or if half quantities are used, as with us, 0.5 c.c.) of the 

 cell suspension sensitized with 2 units of amboceptor, and adding to 

 these tubes varying quantities of guinea-pig serum. The guinea-pig 

 serum is best diluted 1:10 in salt solution, and quantities ranging from 

 0.05 to 0.35 c.c. are added to the tubes. The unit is the amount in the 

 tube which shows complete hemolysis at the end of an hour. The re- 

 actions are usually complete in about 30 minutes. Two units of the com- 

 plement are used in the ordinary test. The titration of the complement 

 is one of the most important steps in accurate work. 



IV. The Sheep Corpuscles. The sheep corpuscles for the actual re- 

 action are obtained by receiving the blood in a small flask containing 

 a sterile solution of a 0.5 per cent sodium citrate and 0.85 per cent 

 sodium chloride, or into one containing glass beads or short pieces of 

 glass tubing. In the former case, the citrate solution prevents clotting 

 and the corpuscles may be washed free from the citrate solution and 

 emulsified in salt solution before use in the test. In the latter case, it 

 is necessary to shake the blood in the flask immediately after taking, 

 and to continue the shaking motion for about ten minutes. The cor- 

 puscles are washed free from serum by at least 3 washings in salt solu- 

 tion. A 5 per cent suspension of the corpuscles is employed for the test, 

 made by measuring the bulk of centrifugalized corpuscles and adding 

 nineteen parts of sterile salt solution. 



V. The Serum to be Tested for Syphilitic Antibody. The serum of 

 the patient is best obtained in the same way that blood is obtained for 

 blood cultures. After surgical precautions, a needle is plunged into the 

 median basilic vein and 3 or 4 c.c. of blood are removed. Before use 



