234 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1950 



acid with another protein, such as sheep serum albumin. The pre- 

 cipitation by the antiserum of such an azoprotein, in which the pro- 

 tein part is completely different from that of the immunizing 

 azoprotein, is evidence that some of the antibodies in the antiserum 

 have a specific combining power with the benzenearsonic acid group. 

 Landsteiner and his collaborators were able in this way to prepare 

 antisera containing antibodies with the power of specific combination 

 with scores of different chemical substances, many of which could 

 hardly be considered to have any natural relation to the injected 

 animal. These results showed that the versatility of the living or- 

 ganism in antibody production is very great, and made it probable 

 that the antibody precursor is to be considered as a plastic material, 

 able to be influenced by the injected antigen in such a way as to obtain 

 directly from the antigen itself the property that leads to the power 

 of specific combination with it. 



Landsteiner and his collaborators also discovered and utilized an 

 important phenomenon, that of hapten inhibition. They found that, 

 for example, when benzenearsonic acid itself is added to an antiserum 

 made by injecting an azoprotein containing the p-azobenzenearsonic 

 acid group no precipitate is formed. Nevertheless, it can be deduced 

 that combination has occurred between the benzenearsonic acid and 

 the antibody, because on addition of an azoprotein containing the 

 ^-azobenzenearsonic acid group no precipitate occurs, although a 

 precipitate would be formed in the absence of the benzenearsonic acid. 

 The benzenearsonic acid is thus shown to have the power of combining 

 with antibody homologous to this haptenic grouping, to form a 

 soluble complex. Information about the strength of the combina- 

 tion of the hapten and of the antibody can be obtained by seeing what 

 concentration of hapten is necessary to prevent the precipitation of 

 the antiserum with a hapten-homologous azoprotein. Landsteiner 

 and his collaborators in this way obtained a great amount of qualita- 

 tive information about the combining powers of various chemical 

 substances with antibodies homologous to haptenic groups of known 

 structure. They found, for example, that not only benzenearsonic 

 acid but also various substituted benzenearsonic acids have the power 

 of combining with anti-^-azobenzenearsonic acid serum, and that the 

 strength of the combination depends upon the nature of the group 

 substituted in the benzene ring and on the position in which it is sub- 

 stituted. Thus, in general, a group substituted in the para position 

 in benzenearsonic acid increases the combining power with anti- 

 7>-azobenzenearsonic acid serum, whereas the substitution of a group 

 in the ortho or meta position decreases the combining power with 

 these antibodies.; 



