The Date of the Discovery of the Capillaries

Abstract

DR. FRASER HARRIS is quite correct in stating that Malpighi (working with Charles Fracassati) demonstrated the existence of blood capillaries with the microscope in the year 1660. The two letters to Joh. Alph. Borelli announcing the discovery were published in folio at Bononia (Bologna) in 1661. This is now a rare tract, and not usually quoted. It is, however, doubtful whether Malpighi first saw capillaries in the frog's lung or in the frog's bladder—;probably it was the latter. Although, of course, he was not the first to practise injection methods, we may note that Malpighi traced the course of the vessels by (a) inflating them; (b) injecting mercury; (c) injecting coloured fluids. Both Sir Michael Foster and your correspondent appear to have overlooked the fact that the expression “Magnum certum opus ocuiis video” is not Malpighi's, but a translation from Homer, and is intended, I imagine, to be translated after the Malpighian manner as: “I see with my eves a truly great work.”