Measurements of the osmotic pressure in the habitat of Polymorphus minutus (Acanthocephala) in the intestine of domestic ducks.

Many of the attempts to culture intestinal helminths in vitro appear to have been made with relatively little knowledge of the physico-chemical conditions which occur in the alimentary tract of vertebrates. For example, only a few measurements have been made on the osmotic pressure of the contents of the intestinal lumen and even fewer have been made on the degree of variation of the osmotic pressure in a given region of the intestine over a period of time. The aims, therefore, of the work described in this paper were to measure the osmotic pressure at different positions in the environment of Polymorphus minutus in the intestine of domestic ducks and to obtain an estimate of the range of osmotic pressures to which the parasite is subjected. These data are required to facilitate the in vitro cultivation of P. minutus and to initiate a study of the osmoregulation of the parasite. The location of the environment of P. minutus in the small intestine of domestic ducks has been described in detail by Crompton & Whitfield (1968). The majority of the worms are found to be attached at positions between 60 % and 80 % of the distance along the intestine with a mean attachment position at about 70 % of the distance along the intestine. During the course of the infection, the mean attachment position changes to about 74 % of the distance along the intestine, a fact indicating that the population of worms migrates posteriorly. The measurements of the osmotic pressure were made by the cryoscopic method of Ramsay & Brown (1955) on small samples of intestinal contents which had been withdrawn through cannulae inserted at known positions into the alimentary tract of ducks. In this way, data were obtained from different regions of the environment of P. minutus over a period of several weeks. A method for studying certain aspects of the physiology of P. minutus and other small intestinal helminths was developed during the course of the work and is also described in this paper.