Abstract
The injection into one rabbit (with Freund's adjuvants) of a specific precipitate made with antibodies from the serum of another rabbit is usually followed by the appearance in the serum of the first rabbit of antibodies which precipitate the serum of certain rabbits but not of others. It was found that the antigen (or one of the antigens) concerned in the reaction of these anti rabbit serum antibodies with rabbit sera had an antibody function, and was therefore a protein. It was concluded that at least one serum protein antigen, the specificity of which so far has been considered to be uniform throughout the animal species, can instead be present in different individuals as different forms or allotypes with somewhat different antigenic specificities.