Axtigex for Precipitation Test 



489 



240 (2200) 



Method of titrating antigen for Kahn precipitation test. 



By R. L. KAHN. 



[From the Bureau of Laboratories, Michigan Department of 

 Health, Laming, Mich.] 



This method aims to overcome variations in antigens em- 

 ployed in the precipitation test for syphilis proposed by the 

 author. Two antigens prepared under identical conditions from 

 two different lots of beef heart, will be likely to show variation 

 in sensitiveness when tested with syphilitic sera. This variation 

 in sensitiveness may be considerably lessened if each antigen is 

 first mixed with salt solution in such proportion as to bring 

 forth its maximum power for producing precipitates with syphil- 

 itic sera. Generally speaking, this is accomplished by mixing 

 antigen with minimum amounts of salt solution which will pro- 

 duce opalescent mixtures. Since the mode of adding salt solu- 

 tion to antigen markedly affects the final product, it is obviously 

 important to render all conditions which are likely to affect this 

 titration as constant as possible. 



The test tubes used in this titration should not differ from 

 those used in the regular tests. In our experience, tubes of 0.8 

 to 1 cm. diameter give best results. The set up of the titration 

 is as follows : 



Six test tubes receive 0.5 c.c. antigen each. Six similar tubes 

 receive respectively 0.25, 0.5, 0.75, 1, 1.25 and 1.5 c.c. salt solu- 

 tion (0.85 per cent NaCl). The 0.25 c.c. salt solution is now 

 poured into the first antigen tube and the mixture immediately 

 poured back and forth several times. The next antigen tube re- 

 ceives the 0.5 c.c. salt solution in a similar manner. The re- 

 maining antigen tubes receive the four increasing amounts of 

 salt solution under similar conditions. It will soon be observed 

 that the first two or three tubes show varying degrees of precipi- 

 tation, the middle tubes, clouding and the last few tubes, opal- 

 escence. 



The salt solution-antigen mixture in which the smallest 

 amount of salt solution is capable of producing opalescence is 

 the salt solution-antigen titre for procedure I. 1 



i Proc. Soc. Exp. Biol, and Med., 1923, xx, 325. 



