The mixed conductor of the invention includes an electron conductor made of a carbon-based inorganic material with a main chain having a \u03c0 bond for conduction of electrons, and a proton conductor made of an inorganic material, wherein the electron conductor and the proton conductor are attached to each other by at least one of covalent bonding, intercalation, and inclusion. The apparatus also includes a heart rate monitor and a timer. The stylet includes a shield release device that moves the shield somewhat out of a handle member of the stylet when the stylet is released from the cannula, so that the safety shield can be more easily grasped.