A multi-element probe comprising: a probe body comprising: a plurality of probe elements, each having a surface suitable for making electrical contact with a tissue of a subject; and an interface, comprising a conductive material, covering the probe-element surfaces, suitable for providing an interface between the elements and the tissue. The shutter member has a resilient-member-fixing portion to which a resilient member is fixed for preventing leakage of the developer through between the shutter member and the developer storing portion. One or more carrier wheels may be provided between the first and second sets of wheels. Also, since the delay circuit is constructed by being incorporated in a DSP for video signal processing, which includes a video signal processing circuit and the like, the construction is simplified. The U-shaped end comprises two branches provided with a blind cylindrical bore designed to receive the cylindrical part of the nails.