Measurements of the Osmotic Pressure in the Habitat of Polymorphus Minutus (Acanthocephala) in the Intensine of Domestic Ducks

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Abstract
1. The osmotic pressure in the environment of Polymorphus minutus in the alimentary tract of ducks has been measured. Samples of intestinal contents were collected through cannulae inserted at known positions into the parasite's environment. 2. Samples were recovered from two healthy living ducks, without inducing anaesthesia, from points at 60% and 80% of the distance along the intestine, and from ten freshly killed ducks at a point 70% of the distance along the intestine. 3. The mean osmotic pressures at 60%, 70% and 80% of the distance along the intestine were found to be 170.5, 171.6 and 178.2 mM-NaCl/1. respectively and the variance was found to be 154.84, 84.41 and 30.13 for the three positions respectively. 4. It is postulated that the greater fluctuations in osmotic pressure at the anterior end of the environment may be responsible for the posterior migration of the parasite during the course of the infection. 5. The method here described for investigating osmoregulation in P. minutus may be of general application for studying aspects of the biology of small intestinal helminths in vivo.