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 of a central region of the fluid-manipulating surface and a corresponding portion of a central region of a specimen-bearing surface of a slide proximate the body ; a first spacer at a first side portion of the fluid-manipulating surface , the first spacer being configured to contact the slide at a corresponding first side portion of the specimen-bearing surface ; a second spacer at a second side portion of the fluid-manipulating surface , the second spacer 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 including a first fluid control element and a second (fluid control element , wherein the first fluid control element is positioned between the first spacer and the first opposable edge , wherein the second fluid control element is positioned between the second spacer and the second opposable edge , wherein the first and second spacers and the first and second fluid control elements ( are all arranged parallel to each other, characterized in that each of the first and second fluid control elements 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 . a body having a fluid-manipulating surface , the body being configured to form a fluid-carrying gap between a portion of a central region of the fluid-manipulating surface and a corresponding portion of a central region of a specimen-bearing surface of a slide proximate the body ; a first spacer at a first side portion of the fluid-manipulating surface , the first spacer being configured to contact the slide at a corresponding first side portion of the specimen-bearing surface ; a second spacer at a second side portion of the fluid-manipulating surface , the second spacer 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 including a first fluid control element and a second (fluid control element , wherein the first fluid control element is positioned between the first spacer and the first opposable edge , wherein the second fluid control element is positioned between the second spacer and the second opposable edge , wherein the first and second spacers and the first and second fluid control elements ( are all arranged parallel to each other, characterized in that each of the first and second fluid control elements 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 . <EOS>