CHAPTER LXrV 



THE KAHN REACTION 



R. L. KAHN 



Bureau of Laboratories, Michigan Department of Health, Lansing, Mich. 

 INTRODUCTORY 



The nature of the precipitation reaction with syphilitic serum and alcoholic ex- 

 ' tract antigen appears to differ from that of the precipitation reaction with specific 

 immune serum. In the former reaction, the precipitate consists largely of lipoids, 

 while in the latter it consists largely of serum globulins. This apparent difference be- 

 tween the two reactions suggested to the writer the necessity for studying the pre- 

 cipitation phenomenon in syphilis as an entity. Several factors were found to govern 

 this phenomenon, and their recognition made possible the construction of a practical 

 precipitation test for syphilis. 



In the latter part of 192 1, the writer observed that within certain limits, concen- 

 tration of a mixture of antigen-saline suspension' and serum hastened precipitation, 

 while dilution of the mixture with saline delayed precipitation. It was noted soon that 

 with an antigen of proper concentration of lipoids it was possible to obtain immedi- 

 ate precipitation reactions with syphilitic serum provided the antigen-saline suspen- 

 sion was sufficiently unstable. An antigen suspension was ultimately prepared which 

 was of such instability that it contained coarse lipoid particles which, however, dis- 

 solved (dispersed) as soon as they came in contact with serum. Then, if the serum 

 came from a syphilitic patient, a precipitate appeared within a few minutes; if it came 

 from an individual free from syphilis, no precipitate appeared. 



The use of an antigen suspension which gave immediate precipitation reactions 

 with syphilitic serum led to the observation of sharp differences in precipitation re- 

 sults due to variation in the proportions of serum and suspension. This could not 

 have been observed readily under conditions of incubation, since some precipitates 

 are enhanced and some redissolved during the incubation period. Ultimately, it was 

 established that optimum precipitation results were obtained only when proper pro- 

 portions of serum and the suspension were employed. Then it was shown that shaking 

 or agitation of the serum-suspension mixture markedly hastened the formation of 

 precipitates. Strongly potent serum, it is true, required but little agitation; weakly 

 potent serum, however, required from two to three minutes' agitation to bring forth 

 the precipitate. 



These four factors which govern the precipitation phenomenon in syphilis, 

 namely, optimum concentration of the ingredients, high instability of an antigen 

 suspension, quantitative relation between the antigen suspension and serum, and 

 agitation of the ingredients, form the foundation on which the writer's test for 

 syphilis was built. The actual evolution of the test required consideration of many 



' The more descriptive term "antigen-saline suspension" or "antigen suspension" is used in this 

 chapter in place of the term "antigen dilution" employed in earlier writings of the author. 



