LACK OF DEPENDENCE OF THE FEEDING REACTION IN HYDRA ON REDUCED GLUTATHIONE

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Abstract
This report takes issue with recent statements that hydras will not eat dead material but are confined to living prey of the Nemathelminthes or higher phyla by exclusive dependence (for initiation of feeding) on reduced glutathione (GSH), which has been characterized as a "feeding hormone." Evidence from the literature, personal observation and experiment, supported by photographs, is offered to show that hydras can feed on Protozoa, algae, mud, other hydras, and flatworms. Ten North American Hydra species, including descendants of Loomis" stock of H. littoralis, have readily ingested dead Daphnia, pieces of beef, horse meat, and hard boiled egg, and bits of washed filter paper or agar gel flavored with dilute solutions of various chemicals[long dash]all uncontaminated with fresh tissue juice or other sources of GSH. Like GSH, dilute quinine hydrochloride has been shown to induce mouth opening, tentacle contraction, ingestion of other hydras and "inert objects," and spreading of the hypostome against the walls of the dish. The prolonged mouth opening and sustained tentacle contraction induced by GSH solutions in the absence of a mechanical stimulus is not a normal feeding reaction. In the concentrations used to demonstrate this behavior, GSH retards swallowing and interferes with feeding. At lower concentrations it may function as one of several substances that can coordinate feeding.