moved in a certain way in saying “I” (ἐγώ).[640] Another noteworthy experiment by Galen was that in which, by binding up a section of the femoral artery he proved that the arteries contain blood and not air or _spiritus_ as had been generally supposed.[641] He failed, however, to perform any experiments with the pulmonary veins, and so the notion persisted that these conveyed “spirit” and not blood from the lungs to the heart.[642] [Sidenote: Did Galen ever dissect human bodies?] It has usually been stated that Galen never dissected the human body and that his inferences by analogy from his dissection of animals involved him in serious error concerning human anatomy and physiology. Certainly he speaks as if opportunities to secure human cadavers or even skeletons were rare.[643] He mentions, however, the possibility of obtaining the bodies of criminals condemned to death or cast to beasts in the arena, or the corpses of robbers which lie unburied in the mountains, or the bodies of infants exposed by their parents.[644] It is not sufficient, he states in another passage,[645] to read books about human bones; one should have them before one’s eyes. Alexandria is the best place for the student to go to see actual exhibitions of this sort made by the teachers.[646] But even if one cannot go there, one may be able to procure human bones for oneself, as Galen did from a skeleton which had been washed out of a grave by a flooded stream and from the corpse of a robber slain in the mountains. If one cannot get to see a human skeleton by these means or some other, he should dissect monkeys and apes. [Sidenote: Dissection of animals.]