stuff. It is my part to-day to show that before motionless stuff-before the problem of the "pri- mum mobile"-even Harvey himself stood help- less; helpless yet fascinated by the indulgence of invention when, in the De motu cordis, or the De generatione, he permitted himself to carry contemplation beyond the sphere of his admirable experiments. "Natural, vital and animal spirits" indeed he would have none of; saying well that he should want as many spirits as functions, and that to introduce such agents as artificers of tissues is to go beyond experience: yet in his need of a motor for his machine he was not able to divest himself of the language nor even of the philosophy of his day; he referred the cause of the motion of the blood, and therefore of the heart, to innate heat'. In his day he could not but regard rest and
¹ Held by Gilbert, and attributed to Averroes; but older than Averroes. In turning to Francis Bacon's hypothesis I read (Ed. E. and S. 11. 263. Hist. Densi et rari-chapter,"Dilatationes per spiritum innatum se expandentem," a Paracelsian sort of chapter) "Pulsus cordis et arteriarum in animalibus fit per irrequietam dilatationem spirituum, et receptum ipsorum, per vices." The muscular quality of the heart was known to Galen, forgotten, and rediscovered. Spiritus vitalis, for Bacon, was "aura composita ex flamma et aere" (cf. En. VL 747). Glisson has been fortunate in two generous judges, in Haller
