234 IMMUNOLOGY 



fore be considered to be effective in peptization and ineffective in 

 precipitation of colloids because it does not disturb the aqueous 

 layer stabilizing the hydrophilic particle." Bancroft (1926) ex- 

 pressed the belief, however, that hydration is not sufficient to ac- 

 count for the Hofmeister series, but that the ions act by shifting 

 the equilibrium aniono- the various pol^^neric forms of water. 



Suppression Phenomenon of Landsteiner. — Landsteiner and 

 Van der Scheer* (1924) call attention to a phenomenon previously 

 studied by Landsteiner: i.e., that "A single precipitin will regu- 

 larly react with other substances if their chemical structure is 

 sufficiently near to that of the homologous antigen." They 

 (1931) have also shown that frequently these chemically similar 

 substances will react with precipitin serum without the forma- 

 tion of a visible precipitate and thus prevent homologous antigen 

 from uniting with the precipitin. This "suppression phenome- 

 non" has been used iDy many in immunochemical studies and is 

 referred to in later chapters. Heidelberger and Kendall (1933) 

 have suggested that the reason visible precipitates do not form 

 in many instances is due to the solubility of rabbit serum globulin. 

 (See Chapter XIX.) 



Haptens. — Attention has been called to the hapten factor in 

 specificity. Type differentiation of red cells is due to the presence 

 of specific chemical substances, nonprotein in nature, coupled 

 with the cellular protein. 



Type specificity of pneumococci is due to nonprotein substances 

 (polysaccharides) that are coupled to the pneumococcus protein. 

 In a later chapter, attention is called to the work of Landsteiner 

 and others who created new antigens by coupling various chemical 

 substances to proteins. The type specific polysaccharides of the 

 pneumococcus and the various chemical substances that are coupled 

 either naturally or experimentally to proteins to create specific 

 antigens have been called haptens by Landsteiner. Naturally oc- 

 curring haptens are very important factors in antigenic specificity 

 as will be seen from a later discussion. It is interesting to note 

 that immune serum will react not only with the protein-hapten com- 

 bination but also with the hapten fraction alone, with the formation 

 of specific precipitates or the fixation of complement or the sup- 

 pression of specific reactions. 



♦Landsteiner and Van der Scheer: J. Exper. Med. 40: 91, 1924. 



