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Blood vessels from the colon (large intestine), coloured scanning electron micrograph (SEM). These vessels are from the capillary bed of the mucous membrane of the colon. This is a cast: the vessels were filled with a resin, which then set. The surrounding tissues were then eaten away chemically, leaving the cast of the vessels. Magnification: x290 when printed 10cm wide. (KEYSTONE/SCIENCE PHOTO LIBRARY/SUSUMU NISHINAGA)