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

Three environmental zones which can influence the activationof the feeding response of Hydra littoralis are termed the macro-,micro-, and ultramicroenvironment. The first consists primarilyof the ions in the bulk medium, and of dissolved gases. Themicroenvironment is the area immediately surrounding the hydra;its composition is influenced by substances emitted from andtaken up by the animal. The third zone, the ultramicroenvironment,is presumed to be made up of a thin shell of ions in the mediumthat are attracted to the charged surfaces of the animal. Through a physicochemical study of these environments, we havedetermined: (1) the presence of ionizable groups at the receptorsite which may be involved in the binding of glutathione; (2)the role of potassium and other ions in influencing the feedingresponse; and, (3) the possible existence of charged surfaceson hydra surrounded by a pH shell. Further, these experimentshelp to resolve many seemingly inconsistent reports dealingwith the feeding behavior of hydras.