IMMUNITY AND ANAPHYLAXIS 203 



having two affinities : one which unites with the antitoxin, 

 the haptophore ; the other, the toxophore, by which the 

 harmful effects are produced. These two affinities are 

 the affinities of two different atom-groups, of which the 

 toxin is supposed to be composed. In the toxoid bodies,, 

 the toxophore group is altered or wanting, but they can 

 still bind antitoxin, in virtue of their haptophore group. 



For other forms of immunity, which are more complex 

 than the toxin-antitoxin one, some elaboration is required. 

 In natural immunity, the blood contains a thermolabile 

 substance which is bactericidal. To this substance 

 Buchner gave the name " Alexine " ; Metchnikoff spoke of 

 it as " Cytase " ; and Ehrlich renamed it " Complement."" 

 In active immunization, a more thermostabile substance,, 

 bactericidal in nature, appears in the serum, and has been 

 variously called "Fixateur" (Metchnikoff), "Substance 

 Sensibilisatrice " (Bordet), "Immune Body or Ambo- 

 ceptor " (Ehrlich). This substance is found to act only 

 in the presence of complement, and hence Ehrlich' s 

 conception that it has two combining affinities which 

 must be satisfied to produce bacteriolysis. The one 

 affinity binds it to complement, the other to the immunizing 

 substance (bacterium or red blood cell, leucocytes and 

 other body cells, toxins, ferments) ; called the Antibody - 

 producer, or Antigen. The immune body he therefore 

 called an amboceptor, or receptor with two hands, which 

 he described as the cytophile haptophore and the comple- 

 mentophile haptophore. He also believes that the 

 complement is composed of two parts, a haptophore 

 group and a zymophore group. According to Ehrlich, the 

 complement is unable to act directly on the antigen or 

 antibody-producer, but only when connected by the 

 immune body or amboceptor. Bordet, however, believes 

 that neither antigen nor immune body has any affinity 

 for complement, until when they are united they can 

 absorb the complement, but not through the immune body. 

 The hypotheses of Ehrlich have been used to explain 

 agglutination, precipitation, and other phenomena, with 

 sundry modifications. It is at present unnecessary to follow 

 the theory further, because in these fields its explanations 

 have been most called in question. This is not to be 



