112 APPLIED IMMUNOLOGY 



gen is as follows : One part of the tissue is minced and 

 mixed with four parts of 96 per cent, alcohol. The 

 antigenic substances are then extracted by shaking the 

 mixture in a machine for 24 hours, when the fluid is 

 filtered or allowed to stand until the sediment falls to 

 the bottom of the vessel. The clear fluid is then 

 pipetted off* and placed in dark bottles, to be used as 

 required. This extract must be tested for antigenic 

 power against a number of known syphilitic and 

 known non-syphilitic sera, and must give positive re- 

 sults with the former and negative with the latter in 

 order to be fit for use. Furthermore, the most suit- 

 able dose must be ascertained. When present in ex- 

 cessive amount, the extract may cause fixation of com- 

 plement alone in the absence of syphilitic serum. The 

 optimal dose of antigen is that which gives complete 

 complement-fixation (or inhibition of hsemolysis) 

 with a syphilitic serum and three times which is re- 

 quired to produce partial fixation without syphilitic 

 serum. Briefly, the optimal dose of antigen should 

 not be greater than one-third the anti-complementary 

 dose. This dose is determined by performing the 

 Wassermann test on a syphilitic serum using several 

 tubes containing the serum and various amounts of an- 

 tigen. Other series of tubes are set up containing 2, 3, 

 and 4 times these amounts of antigen but without 

 syphilitic serum, to determine the anti-complementary 



