IMMUNITY AND HYPERSUSCEPTIBILITY 23 S 



destruction of the side-chains attacked, and in regenerating these 

 the cell over-compensates, the excess side-chains, receptors -of 

 the first order (see page 216), being set free into the blood and con- 

 stituting the antitoxin, which is capable of neutraUzing toxin there 

 or in the test-tube. The assumption of two chemical groups in 

 the toxin molecule is strenghtened by the observation that diph- 

 theria toxin changes on standing so that its poisonous property is 

 much diminished without corresponding loss of ability to combine 

 with antitoxin. Such changed toxin, in which the haptophorous 

 group persists While the toxophorous group has degenerated, is 

 called toxoid. In order to explain the formation and structure of 

 agglutinins and precipitins, EhrHch assigned a more complex com- 

 position to the side-chains which constitute these substances, lead- 

 ing to the conception of a receptor of the second order (see page 

 217), withrits haptophorous and zymophorous groups. In the case 

 of the cytolysins, a further amplification of the idea was necessary 

 to explain the observed fact that the cytolysis is due to two com- 

 ponents, one of which is a thermolabile, normal constituent of the 

 blood and not increased as a result of immunization, the other be- 

 ing a thermostable substance which is produced as a result of the 

 immunization process. This latter immune body, the receptor of 

 • the third order, was therefore pictured as a double receptor (ambo- 

 ceptor) capable of attaching on the one hand the foreign body 

 (antigen) and on the other the normal component necessary to 

 complete the lytic complex, to which component the name comple- 

 ment was given. 



With the recognition of opsonins by A. E. Wright in 1903, 

 the opposing theories of the French and the German schools be- 

 gan to be reconciled, and the relatively simple and largely hypo- 

 thetical theories of immunity began to give way to a more exact 

 and necessarily more complex science of immunology. Bordet 

 and his pupils deserve credit for leading the reaction against too 

 slavish adherence to theory in the study of immunity. Our 

 modern ideas are no longer confined within the scope of any one 

 theory and it is necessary to recognize the existence of a great 



