The method and apparatus serve to treat a multi-walled glass body, in particular a glass body (20) with a glass membrane (25) for a chemical sensor or measuring probe, wherein a portion of at least one wall or of an interior tube (21) is to be fused, and wherein the fusing can have the purpose of closing off a first chamber (291). A glass element (286) which serves to absorb radiation energy is inserted in the vicinity of the portion (210) of either the wall or of the interior tube (21) that is to be fused. The glass element (286) is exposed to the radiation energy of at least one energy radiator (17), whereby the glass element (286) and the portion (210) of either the wall or the interior tube (21) are fused together.