The paper focuses on Pasteur's public experimentation of the anthrax vaccine as portrayed in the English and French popular press of the time. It is argued that this "popular" level of representation did not merely provide additional publicity for Pasteur's ideas. Rather, the nature and meaning of the experiment itself and of the related controversy on immunisation were substantially negotiated and shaped within the public arena. The multifold consequences of this framing at the public level are explored. In particular, attention is drawn to the relationships that in such process were established with other issues debated at the same time in the arena, namely homoeopathy, vivisection and vaccination. The paper shows how Pasteur's ideas were not simply supported, but actively appropriated and manipulated by several groups within the public sphere.