Singularities of lightlike hypersurfaces in Minkowski four-space

An anticoagulant composition for a blood dialysis circuit contains a fatty acid derivative in liquid form at ambient temperature, and an antioxidant. The antioxidant is contained in an amount of 0.0001 to 5.0 parts by weight relative to 100 parts by weight of the fatty acid derivative. An air trap chamber device for a blood dialysis circuit contains a vessel for storing blood dialysed by a dialysis unit, an inlet tube for introducing the blood treated with dialysis into a liquid in the vessel selected from the group consisting of a layer of the aforementioned anticoagulant composition, and the blood, a measurement unit for measuring the pressure of air in the vessel lying above the layer of the anticoagulant composition, an adjustment unit for adjusting the pressure of the air and an outlet tube for conducting the blood treated with dialysis out of the vessel. A method for blood dialysis involves passing blood taken out of a mammal through the aforementioned vessel in which the blood and air are not in contact with each other, and returning the blood into the mammal.