SYPHILIS 123 



the antigen diluted as above, and incubate for ten minutes in 

 the ordinary incubator, or five minutes in a water-bath at 

 37 C. 



Now add i volume of serum from an immunized rabbit, 

 heated, and i unit of the emulsion of the human red cor- 

 puscles. 



Result. The corpuscles will be dissolved. 



Explanation This is a negative Wassermann reaction. 

 The complement does not disappear in presence of this emul- 

 sion of lipoid substances in normal saline solution. 



EXPERIMENT 2. Mix together i volume of fresh serum 

 from an active case of syphilis, untreated, and preferably in 

 the secondary stage, and 4 volumes of the diluted antigen. 

 Incubate as before, and again add immune serum and emul- 

 sion of red corpuscles. 



Result. No haemolysis. 



Explanation. This is a positive Wassermann reaction, 

 and in it the complement has been absorbed, or has disap- 

 peared, when incubated in contact with the emulsion of 

 liquids. Of course, in actual practice a control test, using 

 normal saline solution instead of diluted antigen, is neces- 

 sary to show that the serum contained complement to com- 

 mence with. This is practically always the case with fresh 

 serum. 



This is an example of the Wassermann reaction in its sim- 

 plest form. In the practical application of the test there are 

 several considerations to be borne in mind, and there are 

 numerous methods in use. In the original or classical method 

 the serum to be tested is first heated to destroy complement, 

 and then a certain small amount of guinea-pig 'serum, which 

 contains complement, is added. The mixture with diluted 

 antigen is made much as before, and the whole incubated one 

 hour or more. Then heated serum from a rabbit which has 

 been injected with sheep's corpuscles (anti-sheep serum) is 

 added, and, lastly, an emulsion of sheep corpuscles, washed 

 by repeated centrifugalizations from normal saline, is added, 

 stirred in, and again incubated. Then again, in a positive 

 test, the complement is absorbed, and the corpuscles are not 

 dissolved, whereas in a negative one solution takes place. 

 Exact details are given subsequently. 

 Of the numerous modifications of the process which have 



