Abstract: The bag is formed from two layers of a plastic having properties of mutual superficial adhesion. The layers are laid one on top of the other, and define between themselves at least two chambers each containing a different liquid. To simplify the operations of manufacturing and using the bag, without contaminating the liquids contained in the chambers, the chambers are separated from each other by a separating septum formed by a section of mutual adhesion of the two layers, in which the two layers are in intimate superficial contact. The adherent section is bounded by two lines where the layers are folded to define throttle lines which prevent the liquids from getting from the two chambers into the adherent section. To use the bag, the bag is simply unfolded and pressure is applied to the chambers, in such a way as to cause the layers to come apart in the adherent section and the liquids to mix.