Stimulation by Fatty Acid Salts in Barnacle

As it has been demonstrated that closure of the valves, and changes in the cirral rhythm, of the rock barnacle Balan~ balanaides are reliable criteria of stimulation (Cole, 1932), experiments were made with the salts of the normal aliphatic acids) With a population of 137 animals under constant environmental conditions, the relation between the percentage of closed animals at successive 1 minute intervals and the concentrations of the salts has been determined. The animals were approximately 3 years of age, varying in basal diameter from 8 to 15 mm., and in height from 5 to 12 ram. They were seated on a flat stone, evenly distributed over its surface, and were kept continuously in running sea water for 7 weeks. Temperature was controlled thermostatically at 17.2 40.2°C.; the rate of flow was 250 425 cc. per minute; artificial illumination was constant, and vibrational stimuli were reduced to a negligible minimum. The apparatus was so arranged that the sea water flowing over the animals could be shut off and replaced by the experimental solution at the same rate of flow and temperature, as described in previous papers (Cole, 1928-29; Cole and Allison, 1930-31; 1931-32). The average number of regularly active animals (those showing their normal rhythmic rate) previous to each test was 67, or about 50 per cent of the total. Of the others about 10 per cent were irregular, and about 23 per cent were closed. From four to nine different concentrations of each of the following acids made u p i n 3 liters of sea water were used at the same pH as sea water: formic, acetic, propionic, butyric, valeric, caproic, and heptylic, involving 158 tests. 2 The pH