SOME PHYSIGOCHEMICAL ASPECTS OF THE MACROAND MICROENVIRONMENTS SURROUNDING HYDRA DURING ACTIVATION OF THEIR FEEDING BEHAVIOR

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Abstract
Three environmental zones which can influence the activation of the feeding response of Hydra littoralis are termed the macro-, micro-, and ultramicroenvironment. The first consists primarily of the ions in the bulk medium, and of dissolved gases. The microenvironment is the area immediately surrounding the hydra; its composition is influenced by substances emitted from and taken up by the animal. The third zone, the ultramicroenvironment, is presumed to be made up of a thin shell of ions in the medium that are attracted to the charged surfaces of the animal. Through a physicochemical study of these environments, we have determined: (1) the presence of ionizable groups at the receptor site which may be involved in the binding of glutathione; (2) the role of potassium and other ions in influencing the feeding response; and, (3) the possible existence of charged surfaces on hydra surrounded by a pH shell. Further, these experiments help to resolve many seemingly inconsistent reports dealing with the feeding behavior of hydras.

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