Stimulation by the Mineral Acids, Hydrochloric, Sulfuric, and Nitric, in the Sunfish Eupomotis by William H. Cole* and J. B. Allison

In previous studies on chemical stimulation of aquatic animals it has been assumed that the response measured is a function of the intensity of stimulation of the receptor surface, and that the response may be correlated with the nature of the stimulating substance which initiates a series of energy changes in the heterogeneous system consisting of the chemical environment of the animal and the receptors concerned. The last event in the series activates the neuromuscular mechanism, the efficiency of which is assumed constant in any individual under ordinary conditions. Adaptation and injury must be absent and the energy changes at the receptor surface must be reversible, since the responses are easily reproducible. The original energy change is initiated by the alteration of the ionic or molecular equilibrium and strength of the animal's chemical environment. Stimulation by the primary aliphatic alcohols is evidently a direct effect upon the receptor surface brought about by the addition of alcohol molecules to the environment and by their specific orientation in relation to that surface (Cole and Allison, 1930-31). Since the polar hydroxyl group ( OH) in the alcohols appears to be constant, the predominate factor in stimulation is the field of force around the R group. Similarly, stimulation by the normal primary aliphatic acids in the sunfish (Allison, 1931-32) may be best correlated with the non-polar portion of the molecule, except for the first member of the series where it is necessary to consider the higher potential of the