Vol. LXXV, No. 2 October, 1938 THE BIOLOGICAL BULLETIN PUBLISHED BY THE MARINE BIOLOGICAL LABORATORY THE ACTIVITIES OF VARIOUS SUBSTITUTED PHENOLS IN STIMULATING THE RESPIRATION OF SEA URCHIN EGGS 1 ALBERT TYLER AND N. H. HOROWITZ (From the William G. Kerckhoff Laboratories of the Biological Sciences, California Institute of Technology, Pasadena, California, and the Marine Biological Laboratory, Woods Hole, Massachusetts') INTRODUCTION Whenever a series of related compounds is found to be capable of producing a given physiological effect, there always appears the possibility of relating the activities of the various substances to their molecular structure. In examining such possible relations it is im-portant to distinguish between two different measures of the activity of a substance. Where the effect increases continuously with increas-ing concentration of the substance, the activities may be represented by the concentration required to produce an effect of a definite magni-tude. But if the magnitude of the effect passes through a maximum with increasing concentration of the agent, the activity may be defined by the concentration required to produce the optimum (or maximum) effect or it may be defined by the magnitude of the optimum effect. It is also essential, when more than one molecular species of a substance exists, to determine which is the active form. Without such informa-tion no real comparison of activities can be made, since with different substances the concentration of the active form will depend upon the equilibrium conditions existing between the various molecular species. Due principally to the work of Clowes and Krahl (1936) a large number of substituted nitro-and halophenols are now known that are capable of increasing the respiratory rate of marine eggs. They also exhibit the highly interesting reversible block to cleavage first dem-onstrated by these investigators (1934) with 4,6 dinitro-o-cresol. The effect of these agents is of further interest in that the increased respiratory rate is not accompanied by abnormal development, as is the case with the various oxidation-reduction dyes that had been previously (Barren, 1929; Runnstrom, 1930) shown to stimulate the 1 This investigation was supported in part by a grant from the Penrose fund of the American Philosophical Society. 209 UJ LltRARY V s\ IUJ s
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