8s6 THE KAHN REACTION 



desirable complement fixation procedure in place of the Wassermann test in labora- 

 tories where it is employed in parallel with the Kahn test. 



When considering the relation between precipitation and complement fixation 

 methods, it is important to keep in mind that the interreaction between serum and 

 antigen is essentially the same in both cases. The end-result of this interreaction being 

 readily visible in the precipitation test, no further steps are necessary. The end- 

 result not being visible in the case of the complement fixation test, a special indicator 

 in the nature of the hemolytic system is employed to render it visible. 



NATURE OF THE PRECIPITATION REACTION 



When immune serum is mixed with specific antigen, the resulting precipitate con- 

 sists largely of globulins from the immune serum. When syphilitic serum is mixed 

 with an extract antigen-saline suspension, the precipitate formed consists largely of 

 lipoids. This was shown as early as igii by Jacobstahl. The source of the lipoids is 

 possibly the antigen. This would indicate that the precipitation reaction in syphilis 

 is inherently different from the immune reaction. However, the true nature of the 

 reaction — whether the end-result is the formation of a precipitate or the fixation of 

 complement — is still unknown. Originally, the Wassermann reaction was believed to 

 be a specific immunity reaction. This view was abandoned when it was shown by 

 Landsteiner and others that alcoholic extracts of normal tissue can serve as an antigen 

 in this reaction. 



Recently, Klopstock' was able to elicit positive Wassermann reactions in rabbits 

 following injections with dead Spirocheta pallida. Landsteiner and Van der Scheer^ 

 also recently reported positive Wassermann and Sachs-Georgi reactions in rabbits 

 following injections with dead tr>panosomes. This would indicate that these organ- 

 isms do have antigenic properties. On the other hand, Sachs, Klopstock, and Weil^ 

 obtained positive Wassermann reactions in rabbits after injecting into these animals 

 alcoholic extracts of rabbit organs combined with pig serum. As is well known also, 

 apparently normal rabbits frequently give positive precipitation and Wassermann re- 

 actions. It cannot be concluded, therefore, that such reactions occur only as a result 

 of spirochetal activity. 



As to the mechanism of the precipitation reaction, it is of interest to note that 

 the generalizations deduced from this biological precipitation reaction appear to be 

 closely parallel to some of the essential conditions affecting colloidal precipitation 

 systems of a non-biological character. Thus, in examining the conditions governing 

 the syphilis reaction one may observe several distinct instances of "zone phenomena" 

 typical of colloid reactions. It has, for example, been shown that most sensitive pre- 

 cipitation reactions are obtained with a given antigen when the lipoid concentration 

 is adjusted to a certain optimum value, an increase or decrease in the concentration 

 yielding less sensitive reactions. In this connection it may be noted that little is 

 known of the chemical nature of the antigen excepting that it contains lecithin, 

 cholesterol, and other tissue lipoids. It appears, however, that in its reaction with 

 syphilitic serum the antigen will give desirable precipitation results only after it has 



' Klopstock, F.: Deutsche med. Wchnschr., 52, 226 and 1460. 1926. 



2 Van der Scheer, J.: /. Exper. Med., 45, 465. 1927. 



J Sachs, H., Klopstock, A., and Weil, A. J.: Dc.itsclic med. Wchnschr., 51, 589. 1925. 



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