ANTIGENS 163 



are effected by introducing into the protein molecules substances that 

 are known to combine with the benzine ring, e. g., iodin, diazo- and nitro- 

 groups. Pick, appreciating the fact that the number of different aromatic 

 radicals in the protein molecule are limited, interprets the significance 

 of these radicals as depending upon their arrangement, rather than upon 

 their number, in the protein molecule. Granting the number of possible 

 variations in the arrangement of the aminoacids in a protein molecule 

 which the great number of these radicals provides, there is no difficulty 

 in understanding the possibility of an almost limitless number of specific 

 distinctions between proteins. 



-"I T T ANTITOXINS 



>*"" 45 a* *"" 



.*-; * H ^A 



HEMOLYSINS 



BACTERIOLY3IM5 

 <5v BACTERIOTR0PIN5 

 CYTOTOWN5 



FIG. 43. GENERAL SCHEME OF ANTIGENS AND ANTIBODIES. 



Antitoxins and antif erments : R, Receptor of a molecule of a cell; T, a toxin 

 molecule; t, toxophore group of the toxin molecule; h, haptophore group of the toxin 

 molecule; A, cast-off receptor and constitutes antitoxin. 



Agglutinins and precipitins: A. R, Receptor of cell with antigen attached; B, 

 a bacterial molecule (antigen) attached to a receptor; A or P, an agglutinin or pre- 

 cipitin; h, haptophore group of the antibody; a, agglutinophore group of an agglu- 

 tinin. 



Hemolysins, etc.: A, Cast-off amboceptor (hemolysins, bacteriolysin, etc.); 

 h, haptophore group of amboceptor; c, complementophile group; C, molecule of 

 complement. 



It may be stated, however, in general, that immunologic reactions, 

 such as that of anaphylaxis, are as delicate in distinguishing between 

 proteins as are chemical analyses. Distinctions may be made by these 

 reactions with quantities too small for making accurate chemical de- 

 terminations. 



In succeeding chapters we shall consider, first, the different kinds of 

 immunity, as dependent upon the presence of various factors, and then 

 the role played by the phagocytes and the body-fluids in immunity, 

 with a more detailed consideration of the various antibodies. 



