ERASISTRATUS, fl. 300 B.C., Alexandrian anatomist, was born at Chios, and lived first at the court of Nicanor Seleucus and then at Alexandria, where he formed a school of anatomy. Like Herophilus, he traced the origin of the nerve trunks to the brain and distinguished sensory and motor nerves. But unlike Heroph ilus, he rejected the old humoral pathology and supposed that the arteries contained pneuma or "vital spirits" which, when it escapes, allows the blood to flow from the veins into the arteries, thus making it possible for the arteries to bleed. Any hindrance in the action of the pneuma, or any overflow of the blood into the arteries, resulted in disease, yet, curiously enough, he did not advo cate blood-letting. Erasistratus is to be credited with a detailed knowledge of the convolutions of the brain, the investigation of the bile, spleen and liver, and of the anatomy of the heart, the naming of the trachea, and the invention of a catheter.