The sensory reactions of animals to substances in solution have attracted considerable attention with regard to comparative physiology as well as from the point of view of general physiology. I n vertebrates the chemical senses are commonly grouped into three classes, namely, smell, taste, and the common chemical sense (Parker, '22), the last being in the nature of a general sensitivity of the epithelium to irritating substances. The distinctions between smell and taste have been found to obtain also in insects and certain other invertebrates (see reviews by Koehler, '24, '26; von Frisch, '26; Parker and Crozier, '29). The chemical senses of most invertebrates have been considered as similar to the common chemical sense in vertebrates. Innumerable works have been published dealing with the sensitivity of invertebrates to chemicals of wide variety, comprising compounds ranging from simple inorganic salts to complex organic substances. Certain of these results will be discussed in the following pages.
The present work deals only with some of the inorganic salts which are in man adequate stimuli for taste. The purpose of this investigation was to determine the relative stimulating efficiency of certain salts on the tentacles of the oyster, and in this manner to compare the sensitivity of the oyster with that of other animals for which data are available.