The well-known Wassermann test for syphilis is nothing more than the application of the complement-fixation reaction to diagnostic purposes. It is a method of making the diagnosis of syphilis by demonstrating in the blood (or cerebrospinal fluid, milk, or urine) of the patient a complement-fixing substance not present in normal blood.

The test is twofold: (I) A combination of syphilitic antigen, complement, and suspected serum. (2) A subsequent addition to the mixture of blood-corpuscles and hemolytic amboceptor. If the suspected serum contain the syphilitic antibody, the antigen and the complement unite with it, and the complement being thus "fixed," no hemolysis can take place upon the subsequent addition of the blood-corpuscles and hemolytic serum. If, on the other hand, the suspected serum contain no antibody, the complement cannot be fixed, and is, therefore, free to act upon the subsequently added blood-corpuscles in the presence of the hemolytic serum, and hemolysis results.

It is thus seen that the first test is made for the purpose of fixing the complement, and the second for the purpose of finding out whether or not it has been fixed.

The materials required for the Wassermann test are as follows:

A. Fresh sheep red blood-cells that have been thoroughly washed so as to get rid of any complement.

B. Blood-serum from a rabbit that has been immunized against the blood-cells of a sheep.

C. Immunized rabbit serum (B) that has been heated to 560 C. for thirty minutes in order to destroy the complement, but not affecting the specific amboceptor or immune body which can resist such a temperature.

D. Normal serum from a guinea-pig containing complement.

E. Antigen. Extract of the liver of a syphilitic fetus in alcohol, ether, or water; or lecithin, cholesterin, or extracts from organs of non-syphilitics.

F. Fluid suspected to contain syphilitic antibody (amboceptor). This should be heated to 560 C. for one-half hour to destroy the complement.

For the actual performing of the test there are also needed:

E 1. Serum from a known case of syphilis, containing, therefore, the syphilitic amboceptor. This also must be heated.

E 2. Serum from a known non-syphilitic.

Before using the solutions in the hemolytic series (C and D) they must be carefully standardized, so as to determine just what amount of amboceptor and of complement are necessary in order to cause hemolysis exactly. Such an amount is called a unit.

D, complement.

+

E, syphilitic antigen.

+

F, suspected fluid.

Incubated for one hour at 370 C. Then add.

A, sheep corpuscles.

+

C, hemolytic amboceptor.

The combination of the two systems is placed in an incubator at 370 C. for one hour, then put in the ice-box for twenty-four hours, at the end of which time the final conclusions are drawn.

If F contains the syphilitic amboceptor, it will combine with both D, complement, and E, the syphilitic antigen. Consequently, when A and C of the hemolytic system are added, it will be found that the complement D has been already used or fixed. Therefore no free complement is present to unite with A and C and cause hemolysis. A positive Wassermann is indicated by the absence of hemolysis.

If F does not contain syphilitic amboceptor the complement D will remain free, and when A and C are added, it will combine and cause the destruction (hemolysis) of the sheep corpuscles (A). A negative Wassermann, therefore, is indicated by the presence of hemolysis.

When there is no hemolysis the blood-cells will be in the bottom of the test-tube, and the liquid will be clear and colorless. In hemolysis there may be either a complete or a partial destruction of the red cells, and the overlying fluid will be of a reddish color, the degree depending upon the amount of cellular disintegration.

E 1 and E 2 are employed as controls in the series of tests necessary to determine the accuracy of the solutions that are used in the reactions above mentioned.

A positive Wassermann is nearly conclusive of there being a syphilitic infection. In active syphilis positive reactions have occurred in as much as 94 per cent, of the cases; in latent syphilis, 50 per cent.; and in chronic diseases of the nervous system, as general paresis and tabes dorsalis, the figures vary from 90 per cent, in the first to 50 per cent, in the latter.

On the other hand, a negative Wassermann does not exclude syphilis, as the result may be due to the treatment; as under active treatment with mercury and the iodids, salvarsan, or neosalvarsan the reaction is usually negative.