Definition " variant of the classical serological antibody-antigen reaction consisting of the diffusion of a viral antigen and antibody towards each other through agar [IATE:16174787] gel, which, when they combine, precipitate in the gel producing a visible line with balanced concentrations of antigens and antibody" Reference "COM-EN, based on: Veterinary Laboratory Manual (12.4.2019). Veterinary Laboratory Manual. NSW Department of Primary Industries. 9th edition 2006"