Radial Immunodiffusion Ab-containing gel Precipitin ring o0@⊙ Ag/8 Ag/4 Ag/2 Ag/1 D2 Ring Antigen Concentration Radial Immunodiffusion Ab-containing gel Ag/8 Ag/4 Ag/2 Ag/1 Precipitin ring Antigen Concentration D2 Ring