392 COLLECTED STUDIES IN IMMUNITY. 



by me in diphtheria poisons, depend on the separate destruction of 

 the very unstable toxophore group. 



In passing now to the substances contained in blood plasma I 

 shall discuss first the agglutinins. Even normal serum frequently 

 contains substances which clump certain bacteria and erythrocytes. 

 Although at first, in accordance with Buchner's views, one single 

 substance was made responsible for the different actions, I believe 

 that at present the pluralistic standpoint first maintained by me is 

 generally accepted. The plurality of normal agglutinins was at once 

 proven as soon as my principle of specific combination was applied to 

 this question, as was done by Bordet and Malkow. The latter showed 

 that if goat serum which agglutinates the erythrocytes of pigeon, 

 man, and rabbit is shaken with the red cells of one of these species, 

 e.g. pigeon, it will be found that the centrifuged fluid still contains 

 the two other agglutinins unchanged, whereas the agglutinin for pigeon 

 blood is absent. 



These substances can be obtained artificially by following the 

 procedure of Belfanti and Carbone, who injected animals with con- 

 siderable amounts of foreign red blood-cells (blood-cell immunization). 

 They are readily separated from the hsemolysins developing simul- 

 taneously by heating for half an hour to 56 C. As a result of this 

 the action of the amboceptor iysins is destroyed while the agglutinins 

 themselves are unaffected. To be sure if the temperature is increased 

 to 70 C. it is possible to destroy also the agglutinating action. In 

 that case, however, the addition of normal serum no longer exerts a 

 reactivating action. From this it follows that the agglutinins l are 

 not of such complex constitution as the amboceptor Iysins; analogous 

 to the toxins they contain a haptophore group and a zymophore 

 which causes the coagulation process. In accordance with this I 

 believe that the agglutinins are nothing more than receptors of the 

 second order. 2 



1 The agglutinins here described, in contrast to ricin and abrin, give rise 

 to no further injurious action on the discoplasma. 



2 In the first part of "Schlussbetrachtungen" I have distinguished: 



1. Receptors of the first order, which concern themselves with the assimilation 

 of simple substances (toxins, ferments, and other cell secretions). For this 

 purpose a single haptophore group suffices. When thrust off into the blood 

 in consequence of the introduction of toxins, these receptors constitute the 

 antitoxins (antiferments). 



2. Receptors of the second order, which in addition to the haptophore group 

 possess a second group which effects the coagulation. After they have been 



