LECTURES ON IMMUNITY 



supposes that they, as formed by the injection of an im- 

 mune-body, consist of receptors which bind the same 

 affinity of the immune-body that otherwise might bind the 

 erythrocyte. (Evidently it would be much better to sup- 

 pose, as Ehrlich does in his reply to Bordet, that the 

 antisera may replace the alexins, and therefore do not 

 attack the affinity with which an erythrocyte may be 

 bound.) Then, Bordet retorts, every substance capable 

 of binding the antiserum ought to bind erythrocytes. 

 As we have seen, normal rabbit-serum contains a sub- 

 stance which combines with the antiserum, but not with 

 bovine erythrocytes. Even immune-serum from the rabbit 

 treated with bovine erythrocytes, which serum had pre- 

 viously, by being shaken with ox erythrocytes, been de- 

 prived of substances that bind these erythrocytes, showed 

 an affinity for antiserum. Further, the same antiserum 

 binds immune-bodies which are absorbed by different 

 erythrocytes, as bullock's and hen's, and which are specific 

 for them. 



Hence the attack of Bordet on the side-chain theory in 

 the form of its original application to this phenomenon was 

 quite correct. But this theory possesses a high degree of 

 elasticity, and against the new formulation given by 

 Ehrlich and Sachs in their reply to Bordet, according to 

 which the antiserum competes with the alexin in binding 

 the immune-body, no objection is to be made. 



We might, perhaps, therefore look for a new method of 

 elucidation of this theoretical question. But, as Bordet 

 remarks, Ehrlich has, in his later publications, modified 

 the side-chain theory to such a degree that the differences 

 between Bordet's and Ehrlich's opinions almost disappear, 



