Skin blood vessels. Coloured scanning electron micrograph (SEM) of two small blood vessels (far left and upper right) in the dermis of the skin. In the blood vessels are red blood cells (erythrocytes, red) which carry oxygen around the body. There are some histiocyte white blood cells (yellow) in the tissue around the blood vessel at upper right. These macrophages are called histiocytes when they migrate into tissue to help clear the body of infection by engulfing foreign bodies and dead matter. The blood vessels are surrounded by connective tissue which gives the skin its tone and elasticity. Magnification unknown.