The precipitin reaction provided the first quantitative assay for antibody.

The precipitin reaction is based upon the interaction of antigen with antibody leading to the production of antigen-antibody complexes.

To produce a precipitin reaction, varying amounts of soluble antigen are added to a fixed amount of serum containing antibody.

Upon finishing a dissertation on the antigen-antibody precipitin reaction, he went to Caltech for post-doctoral work, supported by an NIH fellowship.

Precipitin reactions, which determine the absolute and relative amounts of antigen and antibody by measuring the amount of precipitate formed when antibodies mix with soluble macromolecular antigens.

During his 27 years there he used his unique knowledge of polysaccharide antigen chemistry to develop methods, in particular the precipitin reaction, for isolating pure antibodies, which he proved were protein and which he measured in absolute units of weight for the first time.