Precipitation Test for Syphilis 



329 



turbid on standing or in the cold. Since the mode of adding salt 

 solution to antigen markedly affects the final mixture, a method 

 is indicated for this purpose in which tubes of a given calibre are 

 employed; the aim being to produce mixtures which, although 

 clear, are on the verge of precipitation. The employment of a 

 minimum amount of salt solution furthermore eliminates the 

 inhibitory effect of excessive amounts of this solution on specific 

 precipitation of serum and antigen. Assuming therefore that we 

 are dealing with an unstable antigen salt-solution mixture and 

 assuming further that the reacting substances of syphilitic serum 

 are probably also relatively unstable, as indicated by the quanti- 

 tative fluctuations of these substances during the course of the 

 disease, one might expect that mixing these two unstable sub- 

 stances would result in precipitation. 



Dilution of Antigen for Tests : The following method of dilut- 

 ing the antigen with salt solution is somewhat simpler than that 

 described in the earlier communications : 



1. The amount of antigen required for the tests is measured 

 into an agglutination tube of about 0.8 cm. diameter. 



2. Three times the amount of salt solution is added to a sim- 

 ilar tube. 



3. The saline is poured into the antigen tube with reasonable 

 rapidity and the mixture is immediately poured back into the 

 original antigen tube. 



4. This mixture, which is opalescent and shows no signs of 

 turbidity, is now ready for use, although there is no harm in 

 further mixing back and forth. 



The Test: Three-tenths c.c. of serum, previously inactivated 

 for one-half hour at 56° C, is measured into a small tube and 



0. 05 c.c. of antigen-salt solution mixture is added to it, and 

 shaken for about a minute or more. Known positive and nega- 

 tive sera form the controls. The tubes are observed for spon- 

 taneous reactions and the final results are read after overnight 

 incubation at 37° C. Best results are obtained with sera that are 

 clear and to which sheep cells (for removal of natural ambo- 

 ceptor) have not been added. 



Increasing Sensitiveness of Test: If an antigen, after testing 

 with a number of syphilitic sera, appears to lack sensitiveness, 

 the following simple steps will help overcome this difficulty : 



1. The salt solution is chilled by keeping it in the ice-box before 



