An opposable for specimen processing, wherein the opposable is a structure capable of manipulating one or more substances to process a specimen in a tube or on a slide, the opposable comprising: a body having a fluid-manipulating surface, the body being configured to form a fluid-carrying gap between a portion (2016a, 2016b) of a central region of the fluid-manipulating surface and a corresponding portion (2028a, 2028b) of a central region of a specimen-bearing surface of a slide proximate the body; a first spacer (1450, 2018) at a first side portion of the fluid-manipulating surface, the first spacer (1450, 2018) being configured to contact the slide at a corresponding first side portion of the specimen-bearing surface; a second spacer (1452, 2020) at a second side portion of the fluid-manipulating surface, the second spacer (1452, 2020) being configured to contact the slide at a corresponding second side portion of the specimen-bearing surface such that a volume of fluid in the fluid-carrying gap can move in a first direction along the slide while varying a cross section of the fluid-carrying gap in a plane substantially perpendicular to the first direction; a first opposable edge and a second opposable edge; and at least two fluid control elements (1501, 1502) including a first fluid control element and a second (fluid control element, wherein the first fluid control element is positioned between the first spacer (1450, 2018) and the first opposable edge, wherein the second fluid control element is positioned between the second spacer (1452, 2020) and the second opposable edge, wherein the first and second spacers (1450, 1452, 2018, 2020) and the first and second fluid control elements ((1501, 1502) are all arranged parallel to each other, characterized in that each of the first and second fluid control elements (1501, 1502) is formed by a discontinuity in the surface of the opposable, the discontinuity including an edge together with a discontinuous surface beyond that edge, wherein the edge is a stepped edge formed by a cut, a channel, or a break, or wherein the edge is a beveled edge formed by a cut, the beveled edge being concurrent with the respective opposable edge (1454, 1456). a body having a fluid-manipulating surface, the body being configured to form a fluid-carrying gap between a portion (2016a, 2016b) of a central region of the fluid-manipulating surface and a corresponding portion (2028a, 2028b) of a central region of a specimen-bearing surface of a slide proximate the body; a first spacer (1450, 2018) at a first side portion of the fluid-manipulating surface, the first spacer (1450, 2018) being configured to contact the slide at a corresponding first side portion of the specimen-bearing surface; a second spacer (1452, 2020) at a second side portion of the fluid-manipulating surface, the second spacer (1452, 2020) being configured to contact the slide at a corresponding second side portion of the specimen-bearing surface such that a volume of fluid in the fluid-carrying gap can move in a first direction along the slide while varying a cross section of the fluid-carrying gap in a plane substantially perpendicular to the first direction; a first opposable edge and a second opposable edge; and at least two fluid control elements (1501, 1502) including a first fluid control element and a second (fluid control element, wherein the first fluid control element is positioned between the first spacer (1450, 2018) and the first opposable edge, wherein the second fluid control element is positioned between the second spacer (1452, 2020) and the second opposable edge, wherein the first and second spacers (1450, 1452, 2018, 2020) and the first and second fluid control elements ((1501, 1502) are all arranged parallel to each other, characterized in that each of the first and second fluid control elements (1501, 1502) is formed by a discontinuity in the surface of the opposable, the discontinuity including an edge together with a discontinuous surface beyond that edge, wherein the edge is a stepped edge formed by a cut, a channel, or a break, or wherein the edge is a beveled edge formed by a cut, the beveled edge being concurrent with the respective opposable edge (1454, 1456).