Corrosion cast of blood vessels in the brain

The entire vascular (blood vessel) system of a whole animal or organ, down to the smallest capillaries, can be injected with liquid plastic that fills the blood space and rapidly solidifies. The surrounding tissue is then corroded away with an acid or alkaline solution, leaving a hardened cast that accurately represents the form of the original vascular system. With the finest casts made from modern low-viscosity resin, the results can be inspected with electron microscopes, and their geometry mathematically analysed.