Julius Friedrich Cohnheim, a Prussin-born German pathologist, had solved a medical puzzle that vexed scientists for 13 centuries the origin of pus. Cohnheim discovered that pus is the green/yellow liquid that seeps into injured body tissues that is made up of white blood cells that migrate through the walls of capillaries. Cohnheim wrote upon his discovery that "...The so-called pus cells...are colorless blood corpuscles, which forced their way out of the blood vessels..." adding: "There is no inflammation without the participation of blood vessels."

Born in 1839 in Demmin in northern Prussia (present-day Poland), Cohnheim began his medical studies at the University of Berlin when he was 17. Because pursuing his education.

In Berlin, Cohnheim studied under Rudolf Virchow, who was considered the father of cellular pathology. Cohnheim's doctoral dissertation, written under Virchow's supervision, investigated inflammation in serous membranes. He was one of a number of Virchow's students who...