580 COLLECTED STUDIES IN IMMUNITY. 



nation is not the correct one ; as Gay has recently stated, it would in 

 no way affect the soundness of the amboceptor theory. The exist- 

 ence of amboceptors is confirmed by so many experimental consider- 

 ations that it is no longer a postulate of the theory, but is practically 

 the direct expression of observed phenomena. The term amboceptor, 

 of course, is used merely to express the two-sided affinity, to the 

 cell on the one hand and to the complement on the other. The 

 affinity of the amboceptor to the cell was demonstrated by the com- 

 bining experiments published by Morgenroth and myself; and the 

 direct union of amboceptor and complement is confirmed by a host 

 of decisive observations. Of these, it will suffice to mention the 

 test-tube demonstration of complementoids which occupy the com- 

 plementophile groups of the amboceptor. This demonstration has 

 since been effected in other ways (Fuhrmann, Muir, Browning, and 

 Gay), so that the existence of complementoids is no longer evidenced 

 merely by the possibility of producing anticomplements by means of 

 inactivated serum, but is demonstrated primarily by the unmistak- 

 able interference of the complementoids in hsemolytic test-tube 

 experiments. It is not necessary that complementoids should always 

 exert an inhibiting action on haemolysis; for it is obvious that changes 

 in affinity may occur in consequence of external influences, physical, 

 chemical, or chronological in nature. I believe that changes in affinity, 

 either positively or negatively, are of the highest importance in cor- 

 rectly understanding the course of immunity reactions, although I 

 do not deny the influence of certain catalytic factors on these proc- 

 esses (von Behring, Morgenroth, Otto, and Sachs). However, no 

 general rule can be laid down. Experiments are constantly bringing 

 forth surprises, but by diligent empiricism it is usually possible to 

 bring the many different observations into harmony with a single 

 point of view. 



The original assumption, that amboceptor and complement (at 

 least in the case of hsemolysins) exist free side by side, and that the 

 complement does not take part in the reaction until the amboceptor 

 has been bound by the cell (owing to an increase in the affinity of 

 the complementophile group), this assumption has not proven ten- 

 able in every case. In addition to the case described in a previous 

 chapter by Sachs and myself, we now know of a number of combi- 

 nations, discovered by Sachs, in which the amboceptor alone does 

 not unite with the receptor of red blood-cells, or does so to only a 

 slight degree. By combining with the complement, the amboceptor 



