Abstract: A disposable cartridge for use in a clinical sensing arrangement interfaces electrically with a host instrument capable of responding to electrical signals generated by detector devices incorporated in the cartridge upon exposure to calibrant fluids and/or clinical fluids under examination. The cartridge includes a passage linking a reservoir of calibrant fluid to the detector devices and further linking the device to a closed container for fluid which has been conveyed past the devices. A fluid under test can be introducted into the cartridge through the passage wall at a location disposed between the reservoir and the detector devices.