ANTIGENS, HAPTENS, ANTIBODIES, ETC. 413 



mice against Types III and VIII pneumococci, but which 

 confer immunity against Type II organisms. Antigens 

 containing cellobiose or gentiobiose in place of the 

 aldobionic acids give antibodies which are devoid of pro- 

 tective effect against infection with pneumococci. Anti- 

 gens made in the same w^ay using the specific polysac- 

 charides give antibodies with sharp type specificity 

 whilst those containing aldobionic acids give antibodies 

 with a wider specificity covering all types of pneumococci 

 (for example Types II, III and VIII) which contain the 

 same aldobionic acid in their specific polysaccharides 

 (see p. 355). 



Artificial antigens containing strychnine or various 

 sulphonamides, have been prepared by coupling the 

 diazotised substance with a protein. The resulting 

 antibodies react specifically with the antigens. The anti- 

 sera prepared against the strychnine antigen were too 

 weak to protect mice against the toxic effects of strychnine. 

 The specificity of the sulphonamide antigens is determined 

 by the nature of the sulphonamide ; thus sulphanilic 

 acid, sulphanilamide and sulphacet amide azo -proteins 

 give cross reactions with the antisera, whilst sulpha- 

 thiazole and sulphapyridine are much more sharply 

 specific, as would be expected from the difference in 

 the structure of the substituents carried by the sul- 

 phonamide group. 



All the artificial antigens which we have considered 

 so far have been produced by coupling proteins with 

 known simple chemical compounds by means of the diazo 

 reaction. This coupling almost certainly occurs w^ith 

 those amino -acids in the protein, such as tyrosine, histi- 

 dine and tryptophane, which contain aromatic groups. 

 The aromatic nuclei can also be modified in other ways ; 

 for instance, by the introduction of halogens or nitro 

 groups, wdth similar abolition of the original protein 

 specificity and the formation of a new specificity depending 



