Magnetic and counterpart members are immersed in a liquid which may include hard particles. The illumination system includes a light source, an optical fiber bundle, a coupling-in optical system before the optical fiber bundle, a coupling-out optical system after the optical fiber bundle, an illuminating optical system for illuminating an image field, and a homogenizing optical system which is arranged between said coupling-out optical system and said illuminating optical system. The roller 80 serves as a rotor which abuts against the cam 21 so as to drive the fuel injection pump 12, and a roller tappet 82 serves as a support portion for supporting the rotor. A switch contact is carried by the control button and cooperates with a plurality of conductive switch pads. The indicator system can be integrated into a number of products such as sanitary napkins or panty shields and thus can indicate the presence of amniotic fluid or secretions associated with vaginosis without giving a false positive result upon exposure to urine.