ANTIBODIES 165 



When an antigen is altered by heat, it produces an antibody that reacts 

 best with the heated antigen; heating does not, however, destroy the 

 characteristics of the antigen of this species, as its antibody will not react 

 with the heated antigen of another species. (2) The second alteration 

 involves a profound chemical change ,of the antigen, whereby it is so 

 altered that it loses the characteristics peculiar to the species, and pro- 

 duces an antibody that will react with the altered antigen, but not with 

 the unaltered antigen, even from the same animal. For example, it is 

 possible so to alter the serum protein of a rabbit by treatment with 

 nitric acid that the nitroprotein injected back into the same rabbit will 

 produce an antibody specific for the nitroprotein, but which does not 

 react with the unchanged serum protein. These changes are apparently 

 closely related to the aromatic radicals of the protein antigen, for they 



HEMOLYSINS 

 k BACTERIOLY5IW5 

 C\ BACTERIOTROPINS 

 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 pne- 

 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. 



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 



