WASSERMANN AND OTHER COMPLEMENT FIXATION TESTS 241 



And after shaking, the tubes are incubated a second time for i hour, then 

 inspected. 



If the complement was fixed during the first hour of incubation, then there 

 was no free complement in the tube when the rabbit serum and red cells were 

 added; since amboceptor alone cannot destroy antigen, the red cells remain 

 unaltered, they precipitate to the bottom of the tube, and fluid above appears 

 as water, there is no hemolysis. Such is the end appearance of a positive 

 Wassermann test, indicative of syphilis. 



Incubated 



hour 



add 



Again incubate 



i hour 

 no hemolysis. 



If the complement was not fixed, remained free, during the first hour of 

 incubation, then there was free complement in the tube when the rabbit serum 

 and red cells were added. Since complement will join with amboceptor when' 

 that amboceptor's antigen is present and thereby form an antibody that will 

 destroy the antigen, the red cells would be destroyed, the hemoglobin dissolved, 

 the tubes show no sediment, but a clear, transparent red fluid hemolysis. 

 Such is the end appearance of a negative Wassermann test not indicative of 

 syphilis. 



hour. 



add 



Again incubate .] 



i hour 

 hemolysis 



PATIENTS' SERUM FOR THE WASSERMANN TEST 



Only a fraction of a cc. of serum is required for a Wassermann test, an 

 amount that can be obtained from i, 2, 3 cc. of blood, but in all cases it is foolish 

 to withdraw so small an amount. Frequently it is desirable to make the test 

 in duplicate or triplicate; it is well to have an excess of serum that may be kept 

 in storage in case one's findings are questioned, so it can be submitted to several 

 independent workers for reexamination. It is necessary to have known nega- 

 tive and positive sera to control tests and they can only be accumulated by ob- 

 taining from patients more serum than is required for a single examination. 

 No matter how skillful the operator, one does not always withdraw the full 

 amount contemplated before operation. For these reasons it is best to with- 

 draw from 5 to 10 cc. of blood. This blood may be obtained in several ways: 



First. Asepticize a finger, incise it and let the blood flow into a test-tube. 



Second. Asepticize an area over the most prominent vein of the forearm, 

 thrust a needle into it and let the blood flow from the needle into a test-tube. 



Third. Have a sterile syringe attached to the needle that is thrust into the 

 vein, withdraw the blood with the syringe and empty the syringe into a test-tube. 



16 



