The first attempt to isolate and describe fibrinogen, the blood protein essential for clotting. “Prosper-Sylvain Denis, in his Mémoire sur le sang (1859), was the first to recognize that plasma contained a clottable substance, not defined as a liquid fibrin, but different from fibrin, and he attempted to purify and characterize this protein. He independently proposed the name fibrinogène” (Rosenfeld, Four Centuries of Clinical Chemistry, p. 438).