Abstract: A microtiter stick for use in performing immunochemical tests has a solid plastic body and a row of shallow wells (26). Each well is in the form of a truncated hemisphere, the bottom of which is an optically clear, circular, transparent, concave lens surface (26'). The remainder of the truncated hemisphere is stippled to render it translucent thereby to diffuse light and to increase the effective contact surface area of the well. A wall (31) surrounds the upper surface to create a reservoir so that all the wells (26) may be filled at one time. Lens surfaces (36) are formed in the bottom of the stick in optical alignment with the lens surface (26') in each well to create a planar-concave, clear, transparent lens at the bottom of each well.

Abstract: The gas-permeable membrane comprises a reinforcing substrate (2) and a continuous layer (1), deposited thereonto, of a polymer based on an organosilicon rubber. The substrate (2) is made of a solid open-pore material. The layer (1) has a thickness of from 2 to 5 .mu.m and partly fills pores (3). The process for the manufacture of the gas-permeable membrane comprises preparation of a 1-20% solution of a polymer based on an organosilicon rubber in a solvent inert relative to the solid porous substrate material and capable of wetting it. The substrate is heated to a temperature by 0.5.degree.-20.degree. C. above the boiling point of the solvent and the polymer solution is sprayed onto the substrate surface in an amount of from 0.5 to 5 mg/cm.sup.2. The blood oxygenator comprises a plurality of rigid gas-permeable membranes (13) positioned one above another in a housing (17).