[Do objects have history? A meeting between Pasteur and Whitehead in a lactic-acid bath].

Did Pasteur discover, construct, invent lactic acid? This Gordian knot in social studies of the sciences is happily cut when the scene played out at Lille in 1857 is peopled with Whiteheadean conceptual characters. The Nature addressed by Pasteur does not speak the language of scientific utterances but neither is it mute; it is imbued with propositions. Insofar as Pasteur plays the character of a scientist, he is 'acted on' by a singular proposition -- "a tale that perhaps might be told," as Whitehead would say, but that will only be true or false if Pasteur manages to make a real world correspond to this proposition, a world capable of providing logical subjects, and thus offering proof to "whomever judges with impartiality." A hybrid-mediator-translator of Pasteurian and microorganismic propositions, the experimental environment "makes the event," in an encounter from which a new Pasteur and a new yeast emerge, partners of a new history.