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INFECTION AND IMMUNITY 



at all parallel to the fixations obtained with non-specific lipoidal sub- 

 stances. Although we are, at the present writing, still in the dark as 

 to whether the syphilitic antigen depends for its properties upon 

 the lipoidal nature of the extracts or upon the size and disposition of 

 the particles present in the extracts, we can still assert that the test is 

 reliable and, with care in execution and interpretation, of enormous 

 value in the diagnosis of syphilis. However, it is necessary to recog- 

 nize that it is surely not a specific antigen-antibody reaction. 



The antigens most commonly in use today are prepared as follows : 



1. Beef heart or guinea-pig heart muscle is finely chopped up and 

 extracted in five times its volume of absolute alcohol. This mixture 

 is kept 5 to 7 days in the incubator, being frequently shaken. It is 

 then filtered and titrated. Human heart muscle may also be used. 



2. Noguchi's Acetone Insoluble Lipoid Antigen. Fresh spleen is 

 macerated and extracted for 5 to 7 days in the incubator in five times 

 its volume of absolute alcohol, being frequently shaken. It is then 

 filtered and evaporated to dryness with the aid of a fan. The sticky 

 residue is taken up in a small quantity of ether and this ether solution 

 poured into four times its volume of C. P. acetone. The floccular 

 precipitate which forms is collected and can be preserved under 

 acetone. About 0.2 gram of this paste is dissolved in 5 c.c. of ether. 

 This is shaken up with 100 c.c. of salt solution until the ether is 

 evaporated. The resulting antigen is titrated. 



. 3. Chloresterinized Antigen. According to the researches of Sachs 

 and Rondoni, Browning and Cruikshank, and Walker and Swift, 

 antigen can be made more delicate by the addition of cholesterin. 

 Walker and Swift recommend that an alcoholic extract of human or 

 guinea-pig heart be made up to a concentration of 0.4 per cent of 

 cholesterin. 



A large number of other antigens might be mentioned, but we 

 think that the three mentioned above represent the most important, 

 and in principle all of those at present in common use. 



Before an antigen can be used for the actual test, it is necessary to 

 determine the quantity which will furnish a valid result. The sub- 

 stances which are used as antigens often have the power, if used in too 

 large quantity, of themselves binding complement. It is necessary, 

 therefore, to determine the largest quantity of each given antigen 

 which may be used without exerting an anti-complementary action, 

 i.e., which will not inhibit in the presence of normal serum but which 

 will at the same time inhibit hemolysis when syphilitic serum is used. 



