SPECIFICITY 377 



liistidinc-like arsanilic acid haptens and found tliat only the latter 

 would suppress the precipitate when the arsanilic-acid-gelatin anti- 

 gen was mixed with its antisernin. When either of the synthesized 

 haptens was added to the tubes containing arsanilic-acid-egg white 

 and its antiserum, the amount of specific precipitate formed was 

 reduced, and when l)oth synthesized luiptens were added, the pre- 

 cipitate was completely suppressed. This showed that arsanilic acid 

 was coupled to histidine in gelatin and both tyrosine and histidine 

 in the egg white. This agrees with the known respective chemical 

 structures, since gelatin contains histidine but not tyrosine, while 

 Qgg white contains both of these amino acids. In this connection 

 it should be remembered that the formation of a visible precipitate 

 it not essential to the union of antigen and antibody, in fact it is 

 a secondary reaction. It is evident that Landsteiner's suppres- 

 sion phenomenon is due to some form of interference on the part 

 of the unattached hapten added to the antigen-antibody mixture. 

 Apparently it is due to the fact that the formation of immune 

 precipitates is diminished or prevented when the antigen is present 

 in excess (Landsteiner, 1936, p. 119). Its value in determining the 

 nature of an unknown hapten is well established. 



Haptens Responsible for Cross-Reactions. — While some haptens 

 are species-specific, many are not. The latter is indicated by the 

 presence of the "A" and "B" factors of human cells, in the red 

 cells of the anthropoid apes; of a hapten in one strain of Fried- 

 lander's bacillus sufficiently similar to the polysaccharide of Type 

 II pneumococcus, as to be responsible for cross serological reac- 

 tions ; of a hapten in Proteus X19 so similar to one in the Rickettsia 

 of typhus fever, as to make the Felix-Weil reaction possible. Such 

 results enable one to interpret correctly numerous cross-reactions. 



Pneumococcus Type-Specific Polysaccharide Serum Globulin 

 Antigen. — Many immunological facts have been discovered as a 

 result of extensive investigations of haptens carried on for many 

 years. It has been found that when a pneumococcus type-specific 

 polysaccharide is combined with suitable serum globulin there re- 

 sults an antigen which when injected into mice stimulates anti- 

 bodies that protect the mouse against the pneumococcus correspond- 

 ing to the liapten employed. 



Spatial Relationships and Specificity Stereoisomers as Hap- 

 tens. — The possibility that spatial relationship may be one way of 



