There appears to be a common belief among veterinarians that liver-fluke infections, caused by Fasciola hepatica, are only transient and that if the animals do not succumb to the disease the parasites pass out of the body in about nine months' time. For instance, Mönnig's “Veterinary Helminthology and Entomology” states on p. 39: “The flukes (Fasciola hepalica) usually live about 9 months in the sheep and then die and pass out through the intestine.” Clunies Ross & Gordon, in their “Parasites of Sheep in Australia” (1936), say: “The majority of flukes probably die after about 9 months but some at least may survive for 2 years.” One might question on what scientific evidence these statements are based. Thomas (1881), discussing longevity, says with regard to one sheep examined: “The ewe had been kept under conditions which render re-infection highly improbable, and it follows, therefore, that the life of the liver-fluke may extend beyond one year”