The Stimulating Efficiency of the Normal Primary Alcohols. ∗

Abstract

As reported recently, 1 the rhythmic movements of the cirri of barnacles are sensitive indicators of environmental stimulation. A study has been made of the stimulating efficiencies of the first 4 normal primary aliphatic alcohols on Balanus tintinabulum. † The threshold concentration of each alcohol was determined under constant conditions of illumination, temperature and rate of flow, and in the absence of mechanical stimulation. Under such conditions it may be assumed that the stimulating agent is furnishing the minimum amount of energy necessary to activate the receptor. The effects of any secondary processes initiated by excessive stimulation are thus avoided, and the interpretation of the stimulating process is less likely to be erroneous. From the data in Table I it is clear that the stimulating efficiencies of the alcohols increase about 3 fold as each CH₂ group is added, beginning with methanol. This result is similar to that found by previous investigators in studying narcosis, toxicity and related effects. A review of the work and the theories on narcosis has been recently presented by Traube. 2

We have made similar studies on the frog, Rana pipiens. Protecting the animal from all external stimuli, except the alcohol being studied, it has been possible to determine equally stimulating concentrations of the first 5 members of the normal primary aliphatic alcohols. Constancy of reaction time was the criterion for judging equally stimulating solutions. The data, presented in Table II, show that the stimulating efficiencies increase with the number of CH₂ groups. The agreement of these 2 sets of data with the so-called Traube's rule is striking, but we would like to point out that interpretations of stimulation based on surface tension effects alone are probably incomplete.