Precipitation Reaction for Syphilis. 295 



precipitation following incubation is inversely proportional to 

 the amount of salt solution added. The tube, for example, which 

 contains serum and antigen without salt solution may show marked 

 precipitation after 1 hour incubation; the one which contains 

 0.2 c.c. may show moderate precipitation while the one which 

 contains 04 c.c. of salt solution may show no precipitation after 

 the same period of incubation. The above table illustrates this 

 point. 



The question presented itself whether the delay in precipita- 

 tion in those tubes which received salt solution as indicated in the 

 table was due to sodium chloride or the element of dilution. A 

 series of experiments was thereupon carried out employing dis- 

 tilled water, 0.425 per cent, and 2 per cent, sodium chloride 

 solutions and the regular antigen mixture employed in the tests. 

 The results in each case were similar to that obtained with normal 

 salt solution, indicating that the delaying effect is produced by 

 the dilution element and not by the sodium chloride. Of par- 

 ticular interest is the finding that the addition of increasing 

 amounts of antigen exerts the same retarding effect on precipita- 

 tion as, for example, distilled water or normal salt solution. 



132 (1879) 



Relation between serum and antigen in precipitation reaction for 

 syphilis proposed by author. 



By R. L. KAHN. 



[From Bureau of Laboratories, Michigan Department of Health, 



Lansing, Mich.] 



The optimum relation between serum and antigen in the 

 precipitation test for syphilis proposed by the author has been 

 observed to be in the neighborhood of 4: 1. On the basis of this 

 relation one may employ 0.4, 0.3, 0.2 or 0.1 c.c. of serum with 

 0.1, 0.075, 0.05 or 0.025 c.c. of antigen respectively with similar 

 results. This relation holds true also with smaller quantities 

 than 0.1 c.c. Thus 0.04 c.c. of serum with 0.01 c.c. of antigen 

 has been found to give results comparable with 0.4 c.c. of serum 



