In one aspect of the invention, a light emitting device includes a substrate, and a multilayered structure having an n-type semiconductor layer formed in a light emitting region and a non-emission region on the substrate, an active layer formed in the light emitting region on the n-type semiconductor layer, and a p-type semiconductor layer formed in the light emitting region on the active layer. The present invention also provides methods of identifying potential anti-cancer agents by using such tumor cell preparations to identify agents that inhibit EMT, stimulate MET, or inhibit the growth of mesenchymal-like cells. The liquid feed adaptor is largely constituted by a Luer-Lok member having a check valve member fitted on a fore end portion thereof, a stopper ring fitted on the outer periphery of the Luer-Lok member, and a nut member rotatably fitted on the Luer-Lok member for axial displacements between the stopper ring and a flange portion provided at the outer proximal end of the Luer-Lok member.