16
CHR. P. RAVEN
dependent on the electrical charge of the colloid particles. This charge
originates from electrolytic dissociation, and thus is pH-dependent. In
solutions at constant pH, addition of salts also influences the charge.
Cations are fixed on the ionized groups of negatively charged colloids.
This may result in flocculation or coacervation of the colloid. With
logC
FIG. 5. The relation between direct mortality of eggs of Limnaea stagnalis and concentrations of lithium, sodium, potassium, rubidium and caesium chloride. Abscissae:
log. concentration (in equiv./l). Ordinates: per cent mortality.
increasing salt concentrations, the charge of the colloid particles further
decreases, until charge reversal takes place, as can be determined
electrophoretically. If the reversal of charge concentrations of several
cations are arranged in a diagram, a cation spectrum is obtained, which
characterizes the ionized group of the macromolecule in question. For
sulphate and carboxyl colloids cation sequences always correspond to
decreasing atomic weight. This does not hold for phosphate colloids,
where characteristic irregular ion sequences are found. This is explained
by differences in the polarizability of the ionized groups of the colloid
anion with respect to water.
A sequence such as we found for the lethal action of alkali metal ions
on the Limnaea egg agrees with the 'ion spectrum' of reversal of charge
concentrations for phosphate colloids, but differs from that for carboxyl
and sulphate colloids. It was concluded that the effects of the various
cations on the egg were connected with their action on a phosphate
colloid, presumably a phosphatide. The cations of the outer medium, by
being fixed on the phosphatide component of the egg cortex, change the
latter's properties ; at a certain concentration of the cation the normal
physiological properties of the cortex are altered to such an extent that
normal development is no longer possible, and death ensues. The
CHR. P. RAVEN
dependent on the electrical charge of the colloid particles. This charge
originates from electrolytic dissociation, and thus is pH-dependent. In
solutions at constant pH, addition of salts also influences the charge.
Cations are fixed on the ionized groups of negatively charged colloids.
This may result in flocculation or coacervation of the colloid. With
logC
FIG. 5. The relation between direct mortality of eggs of Limnaea stagnalis and concentrations of lithium, sodium, potassium, rubidium and caesium chloride. Abscissae:
log. concentration (in equiv./l). Ordinates: per cent mortality.
increasing salt concentrations, the charge of the colloid particles further
decreases, until charge reversal takes place, as can be determined
electrophoretically. If the reversal of charge concentrations of several
cations are arranged in a diagram, a cation spectrum is obtained, which
characterizes the ionized group of the macromolecule in question. For
sulphate and carboxyl colloids cation sequences always correspond to
decreasing atomic weight. This does not hold for phosphate colloids,
where characteristic irregular ion sequences are found. This is explained
by differences in the polarizability of the ionized groups of the colloid
anion with respect to water.
A sequence such as we found for the lethal action of alkali metal ions
on the Limnaea egg agrees with the 'ion spectrum' of reversal of charge
concentrations for phosphate colloids, but differs from that for carboxyl
and sulphate colloids. It was concluded that the effects of the various
cations on the egg were connected with their action on a phosphate
colloid, presumably a phosphatide. The cations of the outer medium, by
being fixed on the phosphatide component of the egg cortex, change the
latter's properties ; at a certain concentration of the cation the normal
physiological properties of the cortex are altered to such an extent that
normal development is no longer possible, and death ensues. The