Precipitation Test for Syphilis 



327 



color of new extract is the same or more intense than the stand- 

 ard, the extraction may be considered completed. The extract is 

 now filtered off and is kept in the dark at room temperature as 

 stock solution. This extract will keep for at least a year and 

 possibly for many years. 



Antigen prepared from ground heart muscle kept for some 

 weeks or months does not give as sensitive results as that pre- 

 pared from material freshly ground and dried. It has further- 

 more been observed that the non-specific sediments in negative 

 sera following incubation of serum and antigen are due to impu- 

 rities in the extract. These impurities are caused, in most cases, 

 by excessive contact of the extract with cork or rubber stoppers. 



The use of an alcoholic non-cholesterinized antigen for this 

 test has been discussed in previous studies. Further investiga- 

 tions are under way. At present, in routine work, the use of a 

 cholesterinized antigen only is recommended and the procedures 

 discussed below apply to this type of antigen. 



Cholesterimzation of Antigen : A given amount of extract is 

 measured into an Erlenmeyer flask and a quantity of cholesterin 

 added to render it a 0.4 per cent, solution. The cholesterin is 

 dissolved by warming in a water bath with gentle rotation. The 

 solution is then filtered to remove impurities and is ready for use. 



We have recently observed that different lots of alcoholic ex- 

 tract are capable of holding in solution different amounts of 

 cholesterin. Thus, one extract appears to be saturated on adding 

 400 mgm. of cholesterin per 100 c.c, whereas another extract is 

 capable of holding as much as 600 mgm. in solution, and even 

 more. The probable explanation for this is the varying lots of 

 extract, although possessing approximately the same color range, 

 may contain different amounts of lipoid. One may then expect 

 that an extract comparatively poor in lipoids will be capable of 

 dissolving more cholesterin before reaching the saturation point 

 than one which is rich in lipoids. This suggested a method for 

 standardizing the lipoid content of antigens for this test aside 

 from the approximate standardization of these antigens by means 

 of a color range discussed above. The method consists in adding 

 sufficient cholesterin to given alcoholic extracts to bring them to 

 the saturation point at a given temperature. 



An alcoholic extract is capable of holding in solution consid- 

 erably more cholesterin at incubator than at room temperature. 



