He was the first physician to hypothesize that the effects of a stroke were caused by bleeding in the brain. He also mentioned that these symptoms could be caused by a blockage of one of the main arteries that supply blood to the brain. From postmortem studies, he provided information on the carotid and vertebral arteries that supply the brain with blood. in 1658 he published a classic treatise on strokes, titled Historiae apoplecticorum.