. Le bulletin biologique. Biologie ; zoologie ; biologie ; biologie marine. Variation de la densité dans les méduses 209 ont été placés dans un mélange d'eau de mer et de produits chimiques de Percoll (Pharmacia) qui a modifié la densité, mais pas la tonicité de l'eau de mer. Le Percoll est une suspension colloïdale de silice enrobées de polychlorure de vinyle pyrollidone ; elle est non toxique, et présente une faible osmolalité, faible viscosité et de haute densité. Après préparation de tube à dialyse (Brewer el al, 1974), 100 ml de Percoll a été dialysée contre 5 Évolution de 3 litres d'eau de mer plus de 22 heures. La densité de Percoll après la dialyse était 1,148 g/ml. L

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. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. DENSITY CHANGE IN JELLYFISH 209 were placed in a mixture of sea water and Percoll (Pharmacia Fine Chemicals) which changed the density, but not the tonicity of sea water. Percoll is a colloidal suspension of silica coated with poly vinyl pyrollidone; it is nontoxic, and exhibits low osmolality, low viscosity, and high density. After preparing dialysis tubing (Brewer el al, 1974), 100 ml of Percoll was dialyzed against 5 changes of 3 liters of sea water over 22 hours. The density of Percoll after dialysis was 1.148 g/ml. The density of normal sea water with salinity 31.0%o was 1.026 g/ml and density of hypertonic sea water made by adding 8 g NaCl per liter for a final salinity of 38.5%o was 1.034 g/ml. One part dialyzed Percoll was added to 14 parts sea water for a final density of 1.034 g/ml (all measurements at 13-15 °C). Osmolalities of the above mixtures were measured on a Fiske Osmometer and found to be 800 mOsm/kg for 31.0%o sea water, 785 mOsm/kg for Percoll-sea water (1:14 v/v) and 1146 mOsm/kg for 38.5%o sea water. Behavior and relative buoyancies of medusae in the Percoll-sea water mixture were observed for 24 hours. The medusae were then returned to normal sea water in order to check for any subtle adjustments in density (and relative buoyancy) that may have occurred in the Percoll-sea water mixture. RESULTS A standard pattern of events occurred when any species of medusa or ctenophore was introduced to water of a different salinity (Fig. 1). When placed in hypotonic sea water, the jellyfish were relatively dense. Those individuals that had been negatively buoyant or neutrally buoyant at equilibrium in normal sea water sank to the bottom of the experimental beakers; positively buoyant species sank if the drop in salinity HYPOTONIC (23-29%.) NORMAL HYPERTONIC (30-38%0) LAPSED TIME i. Please note that these images are extracted from scanned page images that may have been digitally enhance

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• bookauthorlilliefrankrat
• booksubjectbiology
• booksubjectzoology