DEVELOPMENT OF GASTROPODS
17
differences in lethal concentrations of the ions depend on their affinity
for the reacting sites of the phosphatide.
Furthermore it was found that calcium has a marked antagonistic
effect with respect to the action of lithium (de Vries, 1953) and of other
alkali cations (Raven et ah, 1956; Raven, 1957). When the chlorides of
Li, Na, Κ or Cs are combined with CaCl 2 , then the combinations giving
50 per cent mortality, plotted against the concentrations of both salts,
give a distinct antagonism curve (Fig. 6). The same holds, e.g., for the
600 Γ
CaCI 2 (%)
FIG. 6. The mutual antagonism between lithium chloride and calcium chloride. Thick
line : mixtures of LiCl and CaCl 2 causing 50 per cent mortality of Limnaea eggs. Thin line :
to be expected in case of no interaction.
combination of Li with Na. As the phenomenon of ion antagonism in
model experiments with colloids is characteristic of systems containing
phosphatides, this points again to the importance of phosphatides in
these effects. A peculiarity of the antagonism in case of the eggs is that