I believe that we do not know anything for certain, but everything probably.

Letter to Pierre Perrault, 'Sur la préface de M. Perrault de son traité de l'Origine des fontaines' (1673), Oeuvres Complètes de Christiaan Huygens (1897), Vol. 7, 298. Quoted in Jacques Roger, The Life Sciences in Eighteenth-Century French Thought, ed. Keith R. Benson and trans. Robert Ellrich (1997), 163