SUSCEPTIBLE AND RESISTANT PHASES OF THE DIVIDING SEA-URCHIN EGG WHEN SUBJECTED TO VARIOUS CONCENTRATIONS OF LIPOID-SOLUBLE SUBSTANCES, ESPECIALLY THE HIGHER ALCOHOLS
1. The developing sea-urchin egg when subjected to suitable concentrations of various lipoid-soluble substances—i-amyl, hexyl, heptyl, octyl and capryl alcohols—shows unmistakable rhythms of susceptible and resistant phases, which when taken in connection with the earlier observations of Lyon, Herlant, Mathews, Spaulding, Lillie and others, constitute additional evidence that a very intimate relation exists between the general physiological condition of the egg, and the physical state of its plasma-membrane. 2. During the first ten or fifteen minutes after fertilization the eggs are more susceptible than at any other time until the period just preceding division. A comparatively resistant phase gradually becomes more and more marked up to just before the first cell-division (about 45 or 48 minutes after fertilization). This is followed by a period of decidedly increased susceptibility which lasts for about 15 or 20 minutes, during which time marked cytological effects are noted. Subsequently the resistant phase is largely recovered, and maintained up to the time of the second cleavage. 3. The most favorable concentrations of the various alcohols for demonstrating the rhythm of susceptibility range as follows: i-amyl, between 0.7 and 0.9 vol. per cent.; hexyl, between 0.13 and 0.17 vol. per cent.; heptyl, between 0.06 and 0.07 vol. per cent.; normal octyl, about 0.015; while capryl was considerably above its isomere (normal octyl) between 0.035 and 0.045 vol. per cent. The best records were obtained in experiments using i-amyl and capryl alcohols, possibly indicating a higher specific toxicity of these when compared to the others. 4. When suitable concentrations were used, no marked differences could be detected by varying slightly the durations of exposure. Eggs exposed for five, eight or even ten minutes to the same concentration gave similar results. This, however, would probably apply only within narrow limits.