The fertilization reaction in the sea-urchin egg; the effect of nicotine.

After insemination of unfertilized eggs of Psammechinus miliaris, a change in cortical structure is propagated over the egg surface. A quantitative examination of this phenomenon (Rothschild & Swann, 1949) raised the following questions, requiring further experiments. First, is the observed cortical change the block to polyspermy, or is there a more rapid and so far undetected block to polyspermy as suggested by Gray (1931)? Secondly, is the cortical change directly or indirectly caused by the diffusion of some substance from the sperm head, round the egg surface or through the cytoplasm? The second question is not considered here, though some calculations relating to it have been published elsewhere (Rothschild, 1949).* The first question is the subject of this paper. Hertwig & Hertwig (1887) discovered that nicotine, among other substances, induced polyspermy in sea-urchin eggs. An investigation of the action of nicotine involves consideration of the following possibilities. If nicotine increases the mean speed of a sperm suspension, the number of sperm-egg collisions will be greater than under normal conditions, thus increasing the incidence of polyspermy. Secondly, if nicotine retards or suppresses the block to polyspermy, and the observed change is the block to polyspermy, it should be possible to detect this action of nicotine. Finally, the suggestion has been made that not every sperm-egg collision is successful in the sense that fertilization follows. Nicotine may have a chemical effect on the egg surface such that the probability of a successful sperm-egg collision is increased, with concomitant changes in the incidence of polyspermy. The experiments described in this paper were designed to investigate these questions. Eggs, with and without jelly, and spermatozoa of P. miliaris were used. The fertilization reaction and the movements of spermatozoa were recorded by the dark-ground photography methods described elsewhere (Rothschild & Swann, 1949), while sperm densities were measured with the photoelectric absorptiometer (Rothschild, 1950).