STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Red blood cells and spem. Coloured scanning electron micrograph (SEM). Hematospermia, the presence of blood in semen, is most often a benign symptom. Among men age 40 or older, hematospermia is a slight predictor of cancer, typically prostate cancer. No specific cause is found in up to 70% of cases. Magnification: x3000 when printed 10 centimetres wide.
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