A human heart, showing the arteries and veins which supply blood to the cardiac muscles. The blood vessels, which lie immediately below the surface of the heart, have been injected with dyed gelatine, making visible the smallest capillaries which form this exquisite arterial network. The heart itself has been dehydrated by passing it through increasingly strong solutions of alcohol; it has then been transferred to a clearing agent which makes its surface transparent to a depth of 1-2 millimetres, enabling the blood vessels to become visible. The image was made in black and white hand coloured.