PRECIPITIN TESTS IN SYPHILIS 453 



Table XII 



DISPERSION OF ANTIGEN 



Lsotonic saline, 0.15 e.c, is added to each tube. 



The tubes are shaken for three minutes and incubated in a 37° 

 C. water bath for 15 minutes. 



Salt solution is added after incubation. 



In this titration, 1 c.c. of antigen plus 1 c.c. of isotonic saline 

 is the titer. It is 1 c.c. of the antigen plus a minimum amount of 

 salt solution giving a precipitate wliich dissolves in an excess of 

 salt solution. 



St.vndardization of ANTKiEN. — After the salt titer of the antigen 

 luis been found, comparison wilh tlie standai'd antigen is made 

 as shown in Table XIV. 



Antigens numbers 1 and 2 were freshly prepared antigens. In 

 the comparison, antigen number 1 was almost identical in sen- 

 sitivity and specificity with the standard antigen. Antigen num- 

 ber 2 was unfit for laboratory tests, since it was deficient in 

 sensitivity. Except in the strongly positive serum, the reactions 

 were consistently weaker. In the two very weakly positive sera, 

 negative results were obtained. 



An antigen, standardized as described, consists of coarse particles 

 which, under conditions of the test, are dissolved by an excess of 

 isotonic saline in the presence of normal serum but, wlien filmed 

 with reagin of syphilitic serum, are insoluble and produce coarser 

 macroscopic aggregates. 



Inactivation. — The serum is inactivated by heating at 56° C. 

 for thirty minutes. According to Kahn, sera low in reagin titer 

 which give negative or weakly positive reactions before inactiva- 

 tion, give stronger reaction after heating. No satisfactory ex- 

 planation has been offered. 



Shaking. — After mixing tlie serum and antigen, a three-minute 

 shaking period has been found to give good precipitates with 



