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principles of bacteriology 
than the Wassermann test, and, if equally accurate, 
would be extremely valuable. The best known tests of 
this group are the Sachs-Georgi, the Meinecke, the Dold 
and the Kahn tests, which differ from each other both 
in the technic and the preparation of antigen which, as 
in the Wassermann test, is prepared not from the spiro- 
cheta pallida, but from the beef or the human heart, 
Fig. 40.—Various types of spirochetae. (MacNeal —Pathogenic Organisms.) 
as it has been found that the latter make a better 
antigen than the culture of the spirocheta pallida, thus 
proving that the Wassermann test is a colloidal reaction 
test, rather than the specific antigen-antibody reaction. 
All these precipitin tests are very promising, but the 
final results cannot as yet be foretold. 
