ANTIGENS, HAPTENS, ANTIBODIES, ETC. 405 



Artificial Antigens. — Our knowledge of artificial anti- 

 gens has developed largely as a result of Landsteiner's 

 investigations into the chemical basis of immunological 

 specificity. He showed that if an antiserum is prepared 

 by the injection of, say, horse serum into a rabbit that 

 antiserum will react with horse serum but not with 

 chicken serum or egg albumin. Similarly an antiserum to 

 chicken serum will react only with the homologous serum 

 and not with horse serum or egg albumin, which also 

 gives a specific antiserum. Landsteiner made artificial anti- 

 gens by introducing various known chemical groups into 

 the proteins. For example, he cliazotised the compound 



atoxyl, p-aminophenyl-arsinic acid, NH2;(^ \AeO3Hj, 



and coupled it with proteins, presumably through the 

 tyrosine, histidine or tryptophane groups : — 



CHo.CH.KH,.COOH 



+ 2R.N=N.C1. — 

 + 2NaOH 



OH 



(Tyrosine) 



2NaCl. 



R.N=Nl 'N=N.R 1- ^xxjv 



OH 



(3 : 5 di-azo-derivative) 



He used the resulting atoxyl-azo -proteins as antigens 

 and found that any of the antigens reacted with any of 

 the antisera irrespective of the protein (horse or chicken 

 serum or egg albumin) which was present in the atoxyl 

 derivative. In other words, the atoxyl group had 

 aboHshed (or masked) the original specificity and con- 

 ferred a new one determined by itself. If tlie proteins 



