264 INFECTION AND IMMUNITY 



pension of lipoidal substances constitutes the antigen, and that the 

 complement-fixing complex is made by these antigens in combination 

 with some substance spoken of by Noguchi as "lipotropic" in the 

 syphilitic serum, which has probably no relation to true antibody. 

 Our own work with treponema pallidum antigen would tend to con- 

 firm this, as well as the experience of Noguchi, Craig and Nichols, 

 Kolmer, and others, who have found that a pure treponema pallidum 

 extract gives reactions in only a few late tertiary cases, running not 

 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 dispersion 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 recognize 

 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 fil- 

 tered 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 pre- 

 cipitate which forms is collected and can be preserved under acetone. 

 About 0.2 grams 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. Cholesterinized Antigen. According to the researches of Sachs 

 and Rondoni, Browning and Cruikshank, and Walker and Swift, an- 

 tigen 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 



