bild

Human heart, showing the arteries and veins that 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 that form the 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 original black-and-white photo is here tinted pink. (KEYSTONE/SCIENCE PHOTO LIBRARY/SCIENCE PHOTO LIBRARY)