1) A.v.Leeuwenhock: Observations on animalcula seen in rain, well, sea, and snow water: as also in pepperwater, Phil. Trans., 12, 821-831 (1677).
2) C.H.Håkansson and N.G.Toremalm: Studies on the physiology of trachea. III. Electrical activity of the ciliary cell layer. Ann. Otol. Rhinol. Laryngol., 75, 1007-1018 (1966).