REACTIONS DEPENDING UPON COMPLEMENT FIXATION 305 



should be possible to demonstrate these by bringing them together 

 with spirochetal antigen on the one hand and complement on the 

 other. As shown in Fig. 18, the complement would then be bound 

 to a greater or less extent as the result of the interaction between 

 the other two factors. Since the cultivation of the syphilitic spiro- 

 chete had at that time not been accomplished, however, Wasser- 

 mann was obliged to make use of extracts of organs which were 

 rich in the organisms in question. To this end he employed saline 

 extracts of livers from syphilitic fetuses. With such material as 

 antigen he then actually obtained complement fixation of marked 

 degree, and he very naturally concluded that the reaction which 

 took place was one corresponding to that occurring between a 

 bacteriolytic amboceptor and its corresponding antigen. 



Later studies, however, showed that this could not be the case, 

 since identical results were obtained with alcoholic extracts derived 

 not only from syphilitic organs, but from perfectly normal tissues 

 as well. At the present time we know that the reacting substance 

 of the "antigen" is in no sense a specific constituent of the spiro- 

 chete, but apparently a lipoid of the order of lecithin. The syphilitic 

 antibody accordingly cannot be an amboceptor in the sense of 

 Ehrlich, but is evidently a substance which possesses a marked 

 affinity for certain lipoidal bodies, with which it is capable of inter- 

 acting, with the consequent absorption of complement. Of the 

 nature of this interaction we know nothing. Pending investiga- 

 tions in this direction we may nevertheless represent the process 

 diagrammatically, as I have done above, bearing in mind that in 

 the Wassermann reaction the factors designated as antigen and 

 antibody are so termed only for the sake of convenience. For the 

 antibody in question I would suggest the term, lipoidophilic anti- 

 body, as denoting both its essential characteristic and its nature as 

 a reaction product to infection. 



PREPARATION OF THE REAGENTS. 1. Preparation of the Antigen. 

 While Wassermann originally advocated the use of saline extracts 

 of syphilitic livers, other investigators showed that alcoholic extracts 

 of normal organs (heart, liver, kidney) answer the purpose as well. 

 Noguchi then pointed out that the "antigenic" properties of such 

 extracts essentially belong to the acetone-insoluble fraction, and 

 that undesirable "side" reactions can be avoided by utilizing this 

 fraction only. This I have done for several years and, on the whole, 

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