GENERAL TECHNIC 427 



serve as satisfactory antigens. Boas uses alcoholic extracts of human 

 heart (Michaelis) exclusively, and has found that they yield better 

 results than alcoholic extracts of syphilitic liver. Garbat and others 

 use and recommend similar extracts of guinea-pig heart. 



8. Aqueous extracts of pure cultures of pallida have not thus far 

 yielded results equal or superior to ordinary non-specific antigens. As 

 compared with lipoidal extracts, they have generally yielded reactions 

 that are much weaker, and in primary and secondary syphilis may react 

 entirely negatively. Much is yet to be learned, however, of bacterial 

 antigens in general, and the subject must be regarded as still in the 

 experimental stage. 



It may be said to be well proved that extract antigens in the syphilis 

 reaction are not biologically specific, and need not be extracts of syphilitic 

 tissues. An antigen cannot give reliable or satisfactory results unless it is 

 carefully titrated and its properties determined. Antigens may serve as a 

 frequent source of error when the complement-fixation reactions are con- 

 ducted by those possessing insufficient knowledge of their good and bad 

 properties. The test for the syphilitic reaction should not be undertaken 

 by any one not competent to titrate and judge of the qualities of the antigen 

 to be employed. 



Method of Diluting Antigens. As a general rule, all organic extracts 

 must be diluted with normal salt solution before being used. 



If extracts and diluent are mixed quickly, the emulsion is clear or 

 slightly opalescent. If the diluent is added slowly to the organic extract, 

 the resulting mixture becomes quite turbid and milky. As shown by 

 Sachs and Roudoni, the antigenic power of the extract is more marked 

 with the turbid than when the clear or opalescent emulsion is used. 

 For this reason, in testing for the syphilis reaction the emulsion of organic 

 extract should be made so as to secure the maximum amount of turbidity. 

 The required amount of antigen is placed in a test-tube, and the salt solution 

 is added slowly with a pipet; or the salt solution may be placed in a tube and 

 the extract floated on it and gradually mixed. 



Although with each new extract it may be necessary to titrate with 

 various dilutions before one that is satisfactory is reached, experience 

 has shown in the majority of instances that the following dilutions are 

 usually correct: 



1. Alcoholic extract of syphilitic liver: 1 part with 9 parts of salt 

 solution. Extracts of German manufacture are usually diluted six or 

 seven times. 



2. Cholesterinized extracts and acetone-insoluble lipoids in methyl 



