SPECIAL BACTERIOLOGY 
187 
red blood cells), the complement united with the hemo¬ 
lytic antigen (sheep’s red blood cells) and the hemo¬ 
lytic amboceptor (the rabbit’s serum), hemolysis took 
place, and the contents of the tube became clear. 
As one can now readily see, the test uses two systems: 
the syphilitic antigen and amboceptor (if present) and 
the hemolytic antigen and amboceptor; each system 
equally capable of uniting with the complement. 
Graphically it may be represented as follows: 
Syph. anlbo. 
(patient's serum) 
Syph. antigen 
(preparation of 
spirocheta pallida). 
1. 4. 
\ / 
Complement 
./■ \ 
hemolytic ambo. 
(rabbit’s serum). 
hemolytic antigen 
(sheep’s red blood 
cells). 
If patient has syphilis, his serum has (1) and then 
12 3 combine during the first incubation, (4) and (5) 
have no available complement (3) which is now held 
bound in 1 2 3 combination, no hemolysis takes place, 
and the test is positive. If the patient has no syphilis, 
his serum has not 1, and (4) and (5) combine with 
the complement (3) into the 3 4 5 combination, hemolysis 
takes place, and the Wassermann test is negative. It 
is now clear why the test is also called a complement 
fixation test. 
Precipitation Tests. —Several tests have been offered 
for the diagnosis of syphilis based upon the formation 
of spec'fic precipitins when a proper antigen is mixed 
with patient’s serum and incubated; the precipitin par¬ 
ticles (flakes and granules) can be readily seen with the 
naked eye. These tests are, of course, much simpler 
