Abstract: A device useful for the analysis and measurement of the constituents of solid or liquid media consists of a hermetically closed container containing chemical or biological reactants necessary for the analysis, in liquid, lyophilized or solid form. The container constitutes a hollow space formed in a perforatable material inert with respect to the participants in the reaction. It includes a non-removable rigid cover which is advantageously optically flat at least on its inner surface and optically transparent over at least its central portion. The device and method are applicable to any measurements and analyses, whether manual or automatic, of the constituents of liquid or solid media, notably test samples of biological media.