ISOHEMAGGLUTININS 185 



Nature and Distribution of Red Cell Haptens. — In his study of 

 cellular antigens Landsteinei- (1936) discusses the nature of the 

 haptens which determine blood groups. They are alcohol-soluble 

 substances, probably lipoidal in nature, one for the A and a sec- 

 ond for the B factor. In his opinion they are somewhat analogous 

 in nature to Forssman's antigen. Schiff and Adelsberger (1924) 

 conclude that the A factor in human cells is heterophile in nature 



Fig. S. — Pseudoagglatination or rouleaux formation of red cells. (Microscopic.) 



Figr. 9. — True agglutination of red cells. (Microscopic.) 



since they found group reactions for sheep cells and those of 

 group A (human). It is also of interest to note that the normal 

 antisheep hemolysins frequently found in human blood are re- 

 garded as heterophile antibodies. Landsteiner (1928) suggests 

 that perhaps the antigens of the red cell may have a mosaic 

 structure, since this concept apparently harmonizes with observed 

 phenomena, such as the ease with which antibodies can be frac- 

 tionated by absorption. Recent work by Landsteiner (1936) and 



