"The Uffenbach brothers are visiting Leeuwenhoek in Delft, who shows them several experiments. One of these experiments concerns the demonstration of blood circulation in an eel. For this Leeuwenhoek uses an instrument that Uffenbach illustrates in Fig XI, no. 1 [RKDexcerpt no. 776517], and starts describing on this page. He compares the instrument to Metz's camera obscura."