At 32"×48", this is among the largest works in the collection — and the darkest. Where most of Sidney's abstract works use light grounds and luminous color, Blood Vessel works from the dark outward: the ground is deep purple-black, and the forms that emerge from it do so through internal luminosity rather than surface brightness. The overall effect is of looking into something rather than at something — into a body cavity, into deep water, into space.
The composition is structured around a system of large interlocking biomorphic forms, each outlined in white or pale chalk that gives them the quality of anatomical diagrams — cross-sections, vessels, membranes. In the upper left, a tall narrow blue-green form rises with the vertical authority of a bone or column. At center-left, a large dark spiral — the most completely realized spiral form in the entire collection — coils with genuine three-dimensionality, its interior passages rendered in yellow and green that feel lit from within. To the right, the forms open into deeper dark, with scattered orange sparks and small white marks that suggest cellular activity or distant light sources.
The lower portion of the work contains the most complex passage: a series of interconnected orange-brown and blue-teal shapes that read simultaneously as organs, as geological formations, and as abstract color relationships. A small white figure in the lower left — drawn in thin looping lines — is the most explicitly figurative element in the composition, a tiny human presence at the scale of a bacterium against this vast interior world.
The title Blood Vessel is both literal and metaphorical. Literally, the composition does read like a cross-section of vascular tissue magnified many times. Metaphorically, it suggests both a container of life and a vehicle of passage — the work is about what moves through us, what we are made of at the scale we cannot see.