Abstract: Embodiments disclosed involve methods and constructions for metering, and in some instances combining, fluids. One such method includes fluidly connecting a source of first fluid to be metered with a pressure source capable of moving the first fluid with a first valve and a conduit. The first valve is operated such that first fluid moves in the conduit. The conduit is fluidly connected with a source of second fluid that has a fluid flow rate greater than the first fluid with a second valve. The second valve is operated such that the second fluid moves into the conduit. One construction for metering a fluid comprises a source of first fluid to be metered, a pressure source for moving the first fluid to be metered, and a first valve. A conduit fluidly connects the source of first fluid, the pressure source for moving the first fluid and the first valve such that operation of the first valve causes movement of the first fluid responsive to the pressure source.

Abstract: Homogeneous immunoassays employing double ligand binding conjugates comprising an anti-idiotype binding partner. The anti-idiotype binding partner competes with ligand for an insolubilized ligand specific binding partner. Inhibition of binding of the conjugate to the insolubilized binding partner due to ligand binding permits the second binding partner in the conjugate to bind with insolubilized label means. Thus, detection of label is inversely related to the presence of ligand in the sample.