ON THE PHYSIOLOGY OF AMOEBOID
MOVEMENT.
IV.—THE
ACTION OF MAGNESIUM.
BY C. F. A. PANTIN.
{The Marine Biological Laboratory, Plymouth?)
(Received January 6th, 1926.)
CONTENTS
1.
2.
3.
4.
Maintenance of the cell-surface .
The action of barium .
.
.
The action of cerium .
.
.
Action of Mg" in the presence
of Ca"
5. Interaction of the ions of seawater
297
300
301
302
303
6. The action of Ce'" in the presence of Ca"
. . . .
7. Discussion
8. Summary
9. References
306
306
310
311
T H E previous paper of this series (Pantin, 1926) described the
action of certain ions upon a species of marine amoeba, and
especially the relation of calcium to amoeboid movement. The
same paper detailed the method of preparing isotonic salt
solutions and of determining their effect on amoeboid movement.
The essential feature is that the average velocity is taken as a
measure of the effect of a solution upon the power of movement,
apart from other effects produced upon the cell.
Unless
otherwise stated, the CH of the solutions was maintained at / H
7.0 to 7.2.
1. Maintenance of the cell-surface.
It was shown previously that whereas cytolysis occurred
rapidly in pure isotonic NaCl or KCl (at about />H 7), amoebae
remained alive for a longer time in isotonic CaCl= and
MgClj.
Movement was inhibited in these solutions, but
reversibly, for, provided immersion had been brief, recovery
occurred on return to natural sea-water. In mixtures of two
salts, it was found that movement only occurred if Ca were
297
C. F. A. Pantin
present. On the other hand, the amoeba lived almost as well
in mixtures of (NaCl +MgCl,) as in mixtures of (NaCl + CaCls),
for although no movement took place in the Mg mixture yet
within certain limits of concentration movement was ultimately
resumed on transference of the amoeba to sea-water, even after
some hours immersion.
The same relation was found between solutions of
(KC1 + MgClj) and solutions of (KC1 + CaCl,). But in mixtures
containing only (NaCl+KCl) the permeability of the cell
seemed to increase, and cytolysis occurred rapidly as in pure
NaCl or KC1.
These considerations lead to the conclusion that although
Mg cannot replace Ca with respect to the mechanism of movement, yet either Mg or Ca can ensure stability of the cellsurface. Sr and Ba can also do this. This action seems to be
connected with a reduction of the permeability of the cell which
tends, as is well known, to be brought about not only by Ca
but by Mg or indeed any divalent metal (Osterhout, 1922 ;
Lillie, 1923).
If mixtures of NaCl + MgCl, or of KCl+MgCl s are made
alkaline (J>H 8 to 8.5), a very feeble movement is occasionally
seen for a short time, when the molecular ratio of alkali-metal
to magnesium lies between 5 and 10. This might be expected,
for although there is no Ca in the medium the Mg will prevent
loss of Ca from the cell by lowering the permeability. The
increased alkalinity will also tend to produce movement by
preventing loss of Ca from the actual contractile mechanism
itself, just as it does in solutions of (NaCl + CaCls) deficient in
Ca (Pantin, 1926).
It might be .suggested that if the Mg acts by reducing
permeability an increase in alkalinity of the external medium
could not affect the alkalinity of the cell-interior. But Mg
alone cannot stabilise the cell-surface completely, and the fast
OH-ion may be able to penetrate to some extent. A consideration of more importance is that owing to the continuous
production of CO, in the cell there is a dynamic diffusion
gradient of Ch across the cell-membrane. Raising the C 0H of
the external medium is thus bound to raise the COH just below
the cell-membrane, in order to maintain the steepness of the
398
The Physiology of Amoeboid Movement
gradient. Because of buffer action it is unlikely that there will
be any effect on the protoplasm except immediately below the cellmembrane, at which point the gradient is presumably steepest;
but it is just this region that appears to be most intimately
concerned with the mechanism of amoeboid movement.
If amoebae are placed in a series of solutions of
(NaCl + MgCls), it is seen that, apart from the absence of
movement, the behaviour in the Mg - deficient solutions
resembles that which occurs in mixtures of (NaCl + CaClg)
where calcium is deficient. It is found that in both cases the
adverse changes which lead to death occur successively, commencing in the mixtures where the concentration of the divalent
Mod.tTo.te
FIG. I.—Amoebae in NaCl in the presence of various metals which maintain the cell surface, tut
which will not support movement The distribution of the granules is represented
diagrammatically.
metal is least. Where the molecular ratio is greater than
Na/Mg = 500, swelling and cytolysis occur as rapidly as in
pure NaCl. From solutions containing Na/Mg = 1 2 8 downwards the increasing Mg concentration begins to have a definite
stabilising influence on the cell-surface. The effect increases
more and more rapidly as the Mg concentration is raised till
Na/Mg = 10. The stability is indicated by the longer time
the amoeba remains alive in the solution and the inhibition of
the swelling which occurs in pure NaCl. Osterhout (1922) has
shown parallel changes in the viability of Laminaria in the
presence of increasing concentrations of divalent metals. In
low concentrations of Mg the amoeba assumes an irregular
spherical form : as the concentration increases the amoeba tends
to assume a "proteus" form (fig. 1) and appears more normal.
VOL. in.—NO. 4.
299
u
C. F. A. Pantin
The fact that these changes are closely similar to those
occurring in mixtures of (NaCl + CaClf), although in the Ca
mixtures they are accompanied by movement, supports the
suggestion made- in the previous paper (Pantin, 1926) that the
reduction of movement which occurs in Ca-deficiency is directly
related to an increase in permeability, probably accompanied by
loss of Ca from the cell: this inhibits movement because Ca
is specifically necessary for the mechanism to function.
The similarity of the action of Mg and Ca ceases when the
molecular ratio falls below Na/Mg = 1 0 . In the case of Ca,
an Na/Ca ratio below this value rapidly inhibits movement
and appears to produce a characteristic gelation of the
ectoplasm. But in solutions of NaCl + MgClj the "proteus"
condition seen in lower Mg concentrations is maintained, to
some extent, right up to (Na/Mg = 1.5) and even, for a short
time, in pure MgCla. The viscosity of the protoplasm does
not seem to increase enormously as it does in excess of Ca;
but this is difficult to judge because of the absence of
movement. It may be noted that in experiments conducted by
Professor Chambers and the writer on these amoebae the cellsurface was torn in excess of Ca and of Mg and the medium
freely admitted to the protoplasm : in both cases coagulation
followed. But whereas the coagulum formed with Ca was
exceedingly tough, that formed with Mg was much looser
and "slimy."
In high concentrations of Mg the "proteus" condition
becomes enormously exaggerated.
In such a solution an
amoeba may become reduced to a small central mass of
protoplasm with a dozen or more irregular pseudopodia
radiating from it (fig. 1), in which condition it remains. The
significance of this is not obvious, though it seems to indicate
that the excitor mechanism becomes inco-ordinated.
2. The action of barium.
Like Mg, Ba is able to maintain the stability of the cellsurface but cannot support amoeboid movement. The range
over which stabilisation occurs is approximately the same as it
is with Ca and Mg. Yet the action of Ba seems to be more
closely allied to that of Ca and Sr than to Mg, for like Ca
300
The Physiology of Amoeboid Movement
excess of Ba markedly increases the viscosity of the ectoplasm.
In solutions containing a large proportion of Ba (Na/Ba = 10
or less) the amoeba assumes a form very like that which
occurs in excess Ca and quite unlike the Mg " proteus " form
(fig. i). Very occasionally feeble activity was seen for a short
time in solutions of about the composition Na/Ba = 20, and in
these cases the amoebae approached the unipodal limax type
seen in Ca.
It is possible that Ba not only stabilises the cell-surface
but also acts, like Ca, directly on the contractile mechanism
itself; but although it acts at the same site as Ca the resulting
system does not sufficiently approach the normal conditions to
allow movement.
Although Ba is definitely toxic to amoeba, yet inhibition in
Ba is for a short time reversible where N a / B a > i o .
3- The action of cerium.
Mines (1912) suggested that the action of Mg on various
contractile tissues was essentially connected with the fact that
it is a divalent cation. He showed that, as one might expect,
the far more powerful trivalent cations are able to perform
the function of Mg when they were present in very low
concentration. Osterhout (1922) and Gray (1916) have also
shown that, like Mg, Ce can reduce the permeability of the
cell and is effective in great dilutions. As in solutions of
NaCl + MgClj, amoebae did not move in a solution of isotonic
NaCl in the presence of any concentration of CeCl8. The
solutions were rigidly buffered at pW 6.8 to 7.6 in different
experiments, so this effect is not due to the acidity consequent
on hydrolysis of CeCl8. In a narrow range of low concentration
(io" 5 M), cerium is able to maintain the stability of the cell.
Moreover, there is some approach to the "proteus" form seen
in the presence of Mg (fig. 1). At concentrations below this
{e.g. CeCl8 io" 6 M) is seen the typical swelling and cytolysis
which occurs in pure NaCl.
Raising the concentration of CeCl8 causes rapid coagulation
of the ectoplasm of many of the amoebae, and at a concentration
of i o " ' M almost all are rapidly killed and coagulated. The
ectoplasm often ruptures at the posterior end of the amoeba and
301
C. F. A. Pantin
the endoplasm disperses into the medium where it coagulates,
leaving a hollow "glove" of coagulated ectoplasm.
It is
significant that cerium is only able to maintain the stability of
the cell at a concentration immediately below that at which
irreversible coagulation of the ectoplasm occurs.
Although the action of Ce resembles that of Mg the
resemblance is incomplete. Cerium is far less effective than
Mg in maintaining the normal condition of the cell. However
carefully the concentration was adjusted it was found impossible
to bring about a condition similar to that found in optimum
mixtures of NaCl + MgCl,. Again, a slight excess of cerium
causes complete coagulation and the coagulum is tough,
whereas even in pure isotonic MgCl, no coagulation takes place
for a long time, and the coagulum which is formed even when
Mg is allowed to penetrate the cell is decidedly not tough, but
loose and slimy.
4. Action of Mg in the presence of Ca.
Perhaps the most remarkable observation made throughout
the whole series of experiments was the extraordinarily
complete antagonism found to exist between Mg and Ca.
Cases of antagonism between Mg and Ca are not rare
{e.g. Osterhout, 1922; Loeb, 1906a; Hogben, 1925), but
the effect is usually small and only to be seen when large
amounts of other ions are present. In these amoebae, Mg
and Ca exert a complete antagonism when no other cation is
present.
Good movement takes place in the presence of
(MgCl,+ CaCls) alone, and the range of concentrations of Ca
over which the effect is observed is enormously greater even
than the range over which mixtures of NaCl + CaCl, permit
movement (fig. 2). Almost the only comparable case among
contractile mechanisms which appears to approach the condition
seen here is that recorded by Loeb (1906^) in the cilia of
certain sea-urchin larvae.
These experiments lend the strongest support to the idea
that Mg acts essentially by reducing the permeability of the
cell. In view of the marked inhibiting effect of an excess of
Ca on the one hand, and of its deficiency on the other, in the
absence of Mg, there seems to be no alternative but to suppose
30a
The Physiology of Amoeboid Movement
that Mg prevents the entrance of Ca into the cell when Ca is
present in excess, and prevents its exit when Ca is deficient in
the surrounding medium. This implies that the point at which
Ca acts upon the mechanism of amoeboid movement is not at
the very surface of the cell, but that it lies beneath the surface
film which governs permeability.
We again have evidence in these experiments that the
cessation of amoeboid movement in mixtures of (NaCl + CaCl,)
where Ca is in excess is not due to the action of Ca as a
divalent cation increasing impermeability, but is the result of
its direct specific action on the contractile mechanism. If this
inhibition resulted from decreased permeability, movement
MqCli+ Cadx
pHT
0
• S-5& •'
tOr
1M.
.—o>
/
b-
3
0
•
iff
J4
-t
/
•
Z
o^
If.
8
/6
32
X
- O - - —o
•
r
(Jt
/28
256
Sll
Molecular RatLo
FIG. 2.—Ordinates give per cent, of mean velocity in sea-water.
could not take place in (MgCl s + CaCl,), for both cations
apparently reduce permeability.
It is probably the very
impermeability induced by the Mg which, by preventing
entrance of excess Ca, allows movement to continue.
The enormous range of antagonism of Mg and Ca is only
maintained for a few hours, and even in the central part of the
range movement is much diminished after some sixteen hours
(fig. 2). It follows that the monovalent cations of sea-water
are necessary for completely normal conditions of the cell.
S Interaction of the ions of sea-water.
In view of the preceding experiments it is not surprising
that Mg exerts a marked influence on movement in the
presence of Na and Ca. When a relatively small amount of
Mg is added to mixtures of (NaCl + CaCl,) (fig. 3) the effect is
VOL. III.—NO. 4.
303
U 2
C. F. A, Pantin
to increase slightly the range of concentrations of Ca over which
movement can take place, especially for those weaker in Ca.
The maximum velocity is also increased -slightly and movement
is maintained for a longer period of time. These effects are
greatly increased when the Mg concentration is raised to that
of the Mg in sea-water (fig. 3, curve 2). The increase in the
maximum velocity is in particular enormous, and it now corresponds to a ratio Na/Ca 4= 45 (instead of 20, as in the
absence of Mg), which is the same as that of sea-water.
This shows that in the presence of Mg less Ca is required for
optimum movement.
100
pH8-0
Molecular Ratio:—
W«% -J-5
After
lib
256
Mo/ecalar Rado
FIG. 3.—Effect of addition of Mg to NaCI + CaClg mixtures. Ordinates give per cent of
mean velocity in sea-water.
On raising the concentration of Mg still further the range
of Ca concentrations over which movement takes place increases
for the higher Ca concentrations. For the lower Ca concentrations the range tends to end abruptly (fig. 3, curve 1).
The behaviour approaches that found in simple mixtures of
(MgClj + CaClj) after the lapse of some hours, when the range
has contracted. Infig.7 the absolute concentration of calcium
is not the same for corresponding values of the Na/Ca ratio
of the three curves. The added Mg necessarily dilutes the
mixture so that an Na/Ca ratio of 32 in curves (2) and (3)
corresponds in absolute Ca concentration to an Na/Ca ratio of
about 16 in curve (1).
3°4
The Physiology of Amoeboid Movement
The sudden drop in curve (3) where a large amount of Mg
is present is due to the fact that although the velocity of
individual amoebae tends to increase slightly as the Ca
concentration falls, yet the number of amoebae actually moving
in each dish becomes rapidly smaller. The result is that in
one dish a very few amoebae may be moving well, with a
consequent high average velocity, while in the next dish none
may be moving at all. Had we been dealing with a tissue
such as muscle we could only have observed the statistical
effect of all the cells, and the.resulting curve would have been
quite different in. character.
H7-0
8
NaL+f
K. . 3 2 .
Uf
(28
9ta. Mo)icu)a.T Ratio
256
FIG. 4.—Interaction of the caticmj of tea-water. Ordiaatet give per cent, of mein velocity
in natural sea-water.
In the presence of K as well as Na and Ca, the effects of
adding Mg are still more marked but otherwise similar to those
described above. Fig. 4 shows the effect of adding Mg to
solutions containing Na, K, and Ca, where the ratio Na/K is
the same as in sea-water. When all four ions are present, a
considerable degree of acclimatisation of the amoeba can take
place towards the solution, so that where the proportion of the
salts differs moderately from that of sea-water the velocity may
actually increase for the first twenty-four hours.
Viability is very great in solutions which approach the
composition of sea-water. When the salts are actually in the
same proportions as in sea-water, the velocity of the amoeba
305
C. F. A. Pantin
is the same as in the natural medium within the limits of
variation, and the amoebae will live almost as long as in clean
natural sea-water without food.
6. The action of Ce in the presence of Ca.
We have just seen that the addition of Mg produces a
profound improvement in the movement of amoebae in mixtures
of (NaCl + CaCl,). If cerium is added to mixtures of Na and
Ca, there is perhaps a slight, but certainly not a marked,
improvement, however carefully the Ce concentration is adjusted.
Here again cerium proves to be an imperfect substitute for
magnesium.
7. Discussion.
We have seen that Ca in small quantities is specifically
necessary for amoeboid movement, and only Sr can replace
it. But movement is only maintained for long if the cellsurface be stabilised. The addition of divalent metals such as
Mg or excess Ca will do this, though Ca directly inhibits the
actual mechanism of movement before the concentration is
reached at which the cell-surface approaches complete stability.
Stabilisation is probably connected with reduction of permeability, which prevents both penetration of the medium into the
cell and loss from the cell of certain necessary substances,
particularly calcium.
However, the cell is not completely stabilised when a single
divalent metal is added to a solution of NaCl. Viability is
greatly prolonged if Mg is added to a solution of NaCl which
already contains CaCls, and still further if a small amount
of K is added. Only when all four cations are present
in the proportions of sea-water does the cell remain normal
indefinitely.
The action of K in increasing viability is specific and only
occurs near the Na/K ratio of sea-water. The action in
amoeba is relatively small and is not obviously related to the
varied cases of a specific action of K in many tissues. But
the outstanding features both in these cases and in amoeboid
movement are that only a small amount of K is required to
produce its effect, and that this action of K is shared only by
306
The Physiology of Amoeboid Movement
Rb and, to a less extent, by Cs. Probably K affects
similarly some mechanism common to all cells, such as the cellsurface : whether the observed reaction of the cell relates mainly
to viability, as it does in amoeba, and in developing eggs
(Herbst, 1901 ; Loeb, 1921), or to the marked effects seen in
contractile tissues (Clark, 1921 ; Hogben, 1925), probably
depends on secondary changes peculiar to each type of cell
following initial derangement of this mechanism.
Zwaardemaker (1919) suggests that this action of K is due
to its radioactivity. But Clark (1921) shows this to be unlikely ;
in particular, there is ample K within the cell to provide any
necessary radiation, even though K be removed from the
external medium. It is more probable that the specific action
of K is related to the high K concentration frequently found
within cells (Bayliss, 1924). And it is noteworthy that
Mitchell and Wilson (1921) have shown that Rb and Cs can
partially replace the K normally present in muscle cells: these
are just the two elements which replace K in its "specific"
functions. Possibly the action of K is related to the maintenance
of a potential difference across some surface, as Mines (1912)
suggested, especially since, as Loeb (igo6d) pointed out, the
ionic velocities of K, Rb, and Cs are almost equal to one
another, but considerably greater than those of Li or Na.
Such a potential difference might well be necessary for the
maintenance of the normal permeability of the cell.
Both Mg and K seem to act on the cell-surface, but do
not seem to affect amoeboid movement solely by controlling the
permeability conditions of the cell. Their addition to a solution
of (NaCl + CaCl,) not only affects viability but also greatly
increases the absolute velocity of movement. Perhaps we have
here a single molecular complex in the cell-surface, with two
distinct functions. It may control the permeability of the cell:
this will affect amoeboid movement indirectly by preventing
loss of the normal cell-constituents. But this same complex
may also be a part of the whole mechanism of amoeboid movement itself, and the relation here is direct. The necessity of
Ca for movement involves a separate complex from the one
just suggested, but it also enters into the complete mechanism
of amoeboid movement.
307
C. F. A. Pantin
The cell-surface is evidently an important part of the
mechanism of movement, for direct observation of Umax
amoebae indicates that movement depends on the formation of
gelated ectoplasm from fluid endoplasm at and immediately
below this surface (Pantin, 1923). But the point at which
Ca is specifically required for movement appears to lie below
the actual cell surface : for when the permeability of the surface
is reduced by excess of Mg variation of the Ca concentration of
the medium scarcely affects, the impermeability of the surface
retarding gain or loss of Ca to or from the mechanism. The
Ca is probably required actually in the ectoplasm itself in order
that this may function normally. The direct action of excess Ca
on the viscosity of the ectoplasm confirms this.
Clark (1913) has suggested that in the frog's heart Ca
combines with some lipoid substance to form a soap essential
for the contractile mechanism. Since the action of Ca on
amoeba resembles its action on the heart, it may well be
that some Ca-soap in the ectoplasm is necessary for normal
contractility. The antagonism of the alkali metals and Ca
points in the same direction, for monovalent and divalent soaps
are markedly antagonistic (Clowes, 1916). Moreover, the
properties of alkali metal soaps show a regular gradation with
the atomic weight (Harkins, 1924).
In an earlier paper (Pantin, 1923) certain evidence led to
the idea that a sensitive lipoid surface might control amoeboid
moverrfent. It was suggested that the surface of the cell was
the one in question, but the experiments described above point
to some interface actually within the ectoplasm. Owing to
the continual interchange of ectoplasm and endoplasm in
amoeboid movement this interface cannot be a structure
differentiated from the rest of the protoplasm. But we have
seen that other factors besides Ca affect movement, so such
a Ca-lipoid surface cannot comprise the whole mechanism.
These other factors are related to the action of Mg and K on
the cell-surface. Proteins probably play an important part
here. The tendency to form membranes by concentrating at
surfaces is seen both in proteins and protoplasm. The fact
that cerium, whose action somewhat resembles that of Mg
(Mines, 1913) appears in amoeba only to support the cell
308
The Physiology of Amoeboid Movement
membrane in concentrations where there is incipient coagulation
of the ectoplasm points in the same direction. Moreover, the
ready changes of state, sol ^ t : gel, of the ectoplasm during
amoeboid movement are characteristic of proteins rather than
lipoids.
These considerations indicate that both lipoids and proteins
are involved in the protoplasmic structure on which amoeboid
movement depends, especially near the cell surface.
Now
Loeb (1922) points out that when a protein passes towards
the gel state the protein molecules become held together by
the affinity of the aliphatic, water-insoluble portions of the
molecules, and the ionised terminal groups project into the
surrounding watery medium. If lipoids are present it is
reasonable to suppose that just as two protein molecules are
bound together by their aliphatic parts, so will the aliphatic
end of the- lipoid molecule tend to bind it to the protein
molecule. In view of the work of Langmuir (1922) we may
be justified in considering the gelated surface layers of protoplasm to consist of a network of protein molecules resulting
from the mutual attraction of their aliphatic radicles on to
which is adsorbed a monomolecular layer of lipoid molecules.
The same conditions will obtain, though to a less extent,
throughout the protoplasm.
The advantages of this conception are great. We are at
once provided with two distinct sites at which cations and
other substances can act on the protoplasm, the terminal
(carboxyl) groups of the proteins on the one hand, and of
lipoids on the other. At the same time the two parts of the
complete mechanism are intimately connected, as they appear
to be in amoeboid movement. The action of ions on the
lipoid site may well depend on calcium-soap formation in the
manner suggested earlier.
Cations will also affect the system by combining to form
proteinates (Loeb, 1922). There is reason to suppose that a
large proportion of undissociated metal proteinate may be
formed, as has been shown to occur in gelatine by Northrop
and Kunitz (1924). It may be well to point out that even the
highly ionised NaCl molecules behave as though 25 per cent,
were undissociated, when isotonic with sea-water (Jones, 1912).
309
C. F. A. Pantin
The formation of undissociated proteinates will profoundly
affect the cell. The properties of protoplasm prominent in
amoeboid movement {e.g. swelling, etc.) are seen in pure
proteins in the neighbourhood of the isoelectric point: yet this
point is usually far more acid than the cell interior {cf. Needham
and Needham, 1925). It is probably significant that Northrop
and Kunitz (1924) have shown that undissociated metal
proteinates show effects typical of the Donnan equilibrium as
the concentration of the metallic ion is varied, quite apart from
the effect of the H-ion.
If this hypothesis resembles the truth we may expect that
the primary action of a certain cation will depend upon its
valency electrons. This is practically Mines' hypothesis that
certain ions act by their electric charge. But the action will
not depend solely upon the valency but also upon the
successive dissociation constants corresponding to each valency
electron (Lewis, 1923). It is hoped to discuss these ideas
fully elsewhere.
It therefore seems that in amoeboid movement we must
assume the essential mechanism to be more complex than a
simple lipoid surface, and it is probably significant that in
muscle also Hill (1925) has shown that such a surface cannot
alone account for muscular contraction.
It is very remarkable that the physiology of amoeboid
movement should show such a strong general resemblance to
the physiology of highly differentiated contractile tissues. It
indicates that the properties of the latter depend, far more on
the general nature of undifferentiated protoplasm than upon the
highly specialised structure which they have evolved.
8. Summary.
1. Although movement only occurs if Ca or Sr is present
in the medium, yet Mg and Ba as well are able to prevent the
increased permeability and cytolysis seen in pure NaCl. Cerium
also has a similar action at very low concentrations, but it
is very much less effective than Mg.
2. Excess of Mg never causes the marked increase in
viscosity seen in the ectoplasm when Ca is in excess. For this
and other reasons it seems that inhibition of movement in
310
The Physiology of Amoeboid Movement
excess Ca is due to direct action on the contractile mechanism,
and is not simply the result of decreased permeability.
3. This is borne out by the fact that good movement
occurs in mixtures of (MgCl, + CaCl,) alone, and over a far
greater range of concentrations than occurs in mixtures of
(NaCl + CaClj). This can be readily explained by assuming
that Mg reduces the permeability of the cell so far that Ca
can neither penetrate nor leave the cell and thereby derange the
contractile mechanism.
4. Even in any mixture of (NaCl + CaClj), or of
(MgClg + CaClf), movement gradually falls off.
Only when
all four cations of sea-water are present is movement normal
indefinitely : fully normal permeability is maintained only under
these circumstances.
5. Since the addition of Mg and K to a solution of
(NaCl + CaClg) not only establishes the normal degree of
impermeability but also enormously increases the absolute
velocity of movement, it seems probable that the same
mechanism which controls permeability is also a part of the
whole mechanism of amoeboid movement.
6. The relation of the action of ions to the chemical
structure of protoplasm is discussed.
9. References.
Bayliss, W. M. (1924), Principles of General Physiology, 4th Edition, Longmans,
Green & Co., London.
Clark, A. J. (1913), "The Action of Ions and Lipoids upon the Frog's Heart," Journ.
Physiol., 47, 66.
Clark, A. J. (1921), "The Mode of Action of Potassium upon Isolated Organs,"
Journ. Pharmacol, and Exp. Therapeutics, 18, 423.
Clowes, G. H. A. (1916), "Antagonistic Electrolyte Effects in Physical and Biological
Systems," Science, N.S., p. 75a
Gray, J. (1916), "The Electrical Conductivity of Echinoderm Eggs, etc,"Phil. Trans.
Roy. Soc. B., 80*7, 481.
Harkins, W. D. (1924), Colloidal Behaviour, VoL I. (edited by R- H. Bogue), chap, vi.,
p. 142, M'Graw-Hill Book Co., New York.
Herbst, C. (1901), " Obe» die Entwickelung der Seeigellarven nothwendigen anorganischen stoffe, etc," Arch,/. Entwickmech., 11, 617.
Hill, A. V. (1925), "The Surface Tension Theory of Muscular Contraction," Proc.
Roy. Soc. B., 08, 506.
Hogben, L. T. (1925), "Studies on the Comparative Physiology of Contractile
Tissues," Quart, journ. Exp. Physiol., 18, 263.
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