Tumour blood vessel. Coloured scanning electron micrograph (SEM) of freeze-fractured tissue from a tumour to show the blood supply. The fracture has passed through a small blood vessel (capillary) in which there are red blood cells (erythrocytes, red). The endothelium of the blood vessel (brown) is surrounded by tumour cells (purple) and connective tissue (blue). One of the reasons tumours can grow quickly is because they trigger the formation of new blood vessels to bring blood to the tumour. This tumour is one that arises in the supportive tissues such as bone, fat, cartilage or muscle. It is called a sarcoma. Magnification: x4000 when printed 10cm wide.