in a radiation coagulator having an electric incandescent lamp , in particular a tungsten - halogen low - voltage lamp , as radiation source , and a tissue contact element of a crystalline dielectric material transmissive to the radiation , forming a contact surface to be pressed against living body tissue , the temperature conductivity , the heat capacity of the contact element , possibly in combination with a heat sink attached thereto , is so great that the heat generated in the tissue in contact with said surface is derived in substantial measure from the tissue contact element . this prevents an over - rapid and over - intense temperature rise at the surface of the tissue , leading to a considerable improvement in coagulability , especially for severe parenchymatous hemorrhages , and to lessened adhesion to the contact surface , and permitting a gentle coagulation , extending into depth if desired . besides , the tissue contact element is free from any exposed sharp edges that might cut into the tissue and injure it or cause an excessive concentration of radiation . a preferred material for the tissue contact element is monocrystalline sapphire ; other suitable materials are beryllium or magnesium oxide , or monocrystalline quartz .