ON THE PHYSIOLOGY OF AMOEBOID
MOVEMENT.*
II.—THE
E F F E C T OF TEMPERATURE.
BY C. F. A. PANTIN.
(Assistant Physiologist at the Marine Biological Laboratory, Plymouth.)
IT was shown in the first paper of this series1S that amoeboid
activity was affected by certain changes in the conditions of
the medium in the same way as certain other forms of contractility. This suggested that some fundamental mechanism
of contractility was similar in all these cases.
Like the majority of biological processes, contractility is
affected in a characteristic manner by temperature, and if there
really is a fundamental similarity between amoeboid and other
forms of contractility, the effect of temperature should be
similar in both cases.
i. Material, Methods, etc.
Marine Amoebae, obtained from the laboratory tanks, were
used for the experiments. A full description of the Amoebae,
their habitat and mode of progression, has been given in a
previous paper.16 The Amoebae were of the " Umax " form, that
is, they progressed by the continuous protrusion of a single
anterior pseudopodium. Two species were used, one relatively
"fluid" (type A), and one with relatively "solid," consistent,
protoplasm (type B).
In the absence of external stimuli the Amoebae tend to move
in a straight line. And if the conditions of the medium are
constant the velocity of an individual Amoeba is constant to
within from i per cent, to 5 per cent, for at least twenty-four
hours. This holds true even if the conditions of the medium
have been varied and then brought back to the original state,
provided the variation has not been great enough to damage
the organism.
• Received May 21st, 1924.
C. F. A. Pantin
In these, as in the previous experiments, the velocity of
progression was used as a measure of amoeboid activity. A
"Ghost-micrometer" 4 was placed at such a distance from the
microscope that the lines appeared to be 25 M apart, and the
velocity was measured by timing the Amoeba over a given
number of divisions with a stop-watch.
Harrington and Learning 7 have stated that the conditions
of lighting affect certain Amoebae. A half-watt frosted electric
lamp was therefore used as illuminant in all the experiments.
The temperature was controlled by means of a specially
constructed warm stage. A cell containing the Amoeba was
H
FIG. 1.—Diagram of Warm Stage. The Amoeba is put in the cell A, the top and bottom of
which are sealed with thin glass coverslips. The cell contains about 3 c c of sea water.
Water at a constant temperature flows through the inner chamber B at a slow rate.
The temperature is registered by a thermometer F. The lid, D, is sealed on to the inner
chamber with paraffin wax, P. The inner chamber is protected by an outer chamber, G.
The lid, the inner and the outer chambers are all provided with glass windows (E, C, and H).
K represents the microscope objective (i inch).
completely immersed in a chamber through which flowed a
stream of water at the desired temperature. A thermometer
entering the chamber registered the temperature to TV C.
Details of the construction of the warm stage are given in
fig. i.
Amoeboid activity is influenced by factors other than
temperature {e.g. P H ): the medium employed was always
natural sea water at a constant P H which varied in different
experiments from P H 7.8 to P H 8.2.
2. The Relation of Velocity to Temperature.
The usual procedure adopted was to determine the velocity
at about 15° C , and then to lower the temperature by successive
intervals to the critical point at which activity was inhibited.
520
The Physiology of Amoeboid Movement
The temperature was then raised by intervals until movement
ceased owing to the destructive effect of the high temperature
upon the protoplasm.
The velocity was measured five to ten minutes after each
change of temperature to allow the Amoeba to become
acclimatised to the new conditions. However, the velocity
usually became constant in about one minute, unless the
temperature was close to either critical point at which all
movement ceased. Since the warm stage itself takes from a
half to one minute to attain a constant temperature after each
change, acclimatisation is probably rapid except near the
critical temperature.
The velocity of both kinds of Amoebae studied varies
markedly with the temperature. Fig. 2 shows a typical
curve obtained from a type B Amoeba. The experiment
was commenced at I5.2°C. ; the temperature was then
lowered successively (through points 2 to 6) to — 2.00 C ,
and then raised.
From just above o°C. to i5°C. the velocity is approximately
proportional to the centigrade temperature. For this Amoeba
there is a distinct " l a g " in the velocity obtained with a rising
temperature; that is, the velocity at 10° is higher if approached
from a high temperature than if approached from a low one.
This " l a g " was not always observed in other Amoebae.
The rate of increase of velocity falls rapidly above 17.50 C ,
so that the velocity itself reaches a maximum at about 200 C.
After this the velocity falls rapidly to zero at 260 C , though
death does not occur rapidly (within ten minutes) until 30° C.
These points are well shown in fig. 3, which shows the
mean curve obtained from experiments on ten Amoebae. For
each Amoeba the velocities measured were reduced proportionally to the same scale so that the value at io°C. was approximately 1.00. The mean velocity was then taken for each 2.5°
rise in temperature.
Like the majority of biological processes, amoeboid activity
is inhibited a few degrees below o° C. This inhibition is completely reversible: even if the Amoeba has been kept for some
time at - 30 C , yet on raising the temperature, recovery takes
place within a few minutes and the Amoeba moves with the
5"
C. F. A. Pantin
speed characteristic of the temperature, except in cases which
show the slight " l a g " effect already described.
Again, as in other processes, the activity rises with the
temperature to an optimum, the position of which shows slight
a
20
0
30C
FlG. 2.—Variation of velocity with temperature for a single type B Amoeba. The numbers
and arrows indicate the order in which the values were determined.
individual variation, and above this optimum activity falls
rapidly to zero.
The fall in velocity above the optimum (figs. 2, 3, and 4)
may be partly due to failure of the method. Above the
522
The Physiology of Amoeboid Movement
optimum the Amoeba moves rather irregularly and tends to
form lateral pseudopodia : with this loss of the limax form, the
velocity is no longer so accurate a measure of the activity of
the Amoeba.
However, the optimum for amoeboid activity is of the same
20°
FlG. 3.—Mean variation of velocity with temperature for 10 type B Amoebae.
to scale (velocity at IO° = IJD).
30°C.
Velocity reduced
A, B, and C are extrapolated values referred to in the text
character as the optima of other processes ; if the temperature
be raised above it until activity is inhibited we find that the
inhibition is only partially reversible, as in other processes
{e.g. ciliary activity 6 ). Type B Amoebae were found to require
several hours to recover after inhibition at a temperature above
the optimum, and type A Amoebae rarely, if ever, recovered
after complete inhibition by heat.
5*3
C. F. A. Pantin
The low temperature of the optimum is of interest; it is
always about 20° C. for type B, and 22° to 2 5°C. for type A.
This low optimum does not appear to be general for all cases
of amoeboid activity, because McCutcheon M has shown that the
optimum for human leucocytes occurs at 40° C , as might be
expected. Moreover, it seems probable that many freshwater
Amoebae can withstand temperatures actually above the deathpoint of these marine Amoebae.
3. The Fall in Velocity above the Optimum.
The occurrence of an optimum activity suggests that above
this point destructive forces begin to act on the mechanism.
Gray 6 has suggested that the fall in ciliary activity above the
optimum temperature might be due to the destruction of an
enzyme: the argument applies also to amoeboid activity,
although in this case the optimum is very low.
The following experiments show definitely that the fall in
amoeboid activity is due to the destruction of some mechanism
in the protoplasm. The velocity of a type B Amoeba was
determined at 10° C.; the temperature was then suddenly raised
and maintained at a higher value for ten minutes ; at the end
of this time the temperature was suddenly lowered again to
io° C , and the velocity of the Amoeba measured at intervals.
At first the velocity was below its initial value at io° C , but
recovery gradually took place. The times for recovery for
different temperatures are given in Table I. The values were
obtained successively with the same Amoeba.
TABLE 1.
Initial
Velocity measured at 10° C.
Time required for
recovery at 10° C.
0 minutes
3-4
,.
20
„
70
„
20
„
32
about 240
„
Temperature changed
to T° C. for ten minutes.
T = 15-3° C.
17-6
[optimum) 20-0
21-9
20-5
21-3
22'5
These experiments definitely show that high temperatures tend
to destroy something necessary for amoeboid activity, and that
524
The Physiology of Amoeboid Movement
the amount of destruction increases very rapidly with the
temperature above the optimum. They also show that a
limited amount of destruction has taken place before ever the
optimum is reached. In the experiment quoted the Amoeba
required three to four minutes to recover the normal velocity
after the temperature had been raised to 17.6° C , that is 2.50
below the optimum.
One of the factors upon which amoeboid activity depends
is therefore some substance or structural arrangement of
substances which is rapidly destroyed near and above the
optimum temperature. If this substance is partially destroyed
or is present in less than the normal amount, the velocity of
the Amoeba is proportionately lower, though otherwise the
behaviour is normal. This is shown in fig. 2.
In that experiment, immediately after the Amoeba had been
paralysed by being heated to 26.30 C, the temperature was
lowered to I5.8°C, and the Amoeba allowed to recover.
Thirty minutes later it had only partially recovered and the
velocity was proportionately below the normal for that
temperature (point 16). On now raising the temperature the
relative increase in velocity was about the same as in the
normal Amoeba (point 17), but the velocity was still below its
normal value for this temperature. It might be said that the
Amoeba was following the normal temperature curve on a
reduced scale, the reduction being proportional to the amount
of the substance or structure that had yet to be re-formed by
recovery.
4. Extrapolation of the Velocity: Temperature Curve.
It has been shown that the fall in velocity above the
optimum is due simply to a destructive effect. In the absence
of this effect the velocity should continue to rise above the
actual optimum in continuation of the lower, normal part of the
velocity : temperature curve.
If allowance could be made for the destructive effect we could
thus extrapolate the normal part of the velocity : temperature
curve. This would be of great value because the limited range
over which the normal curve extends makes it difficult to compare
with the temperature curves of other physiological processes.
VOL. 1.—NO. 4.
525
aM
C. F. A. Pantin
The destructive effect may be allowed for approximately in
the following way. Assume that an Amoeba moves with a
velocity, V10, at 10° C. Let the temperature be raised above
the optimum to T° C. for a certain time. If there were no
destructive effect the velocity at T° would be VT, the velocity
having continued to rise with the temperature as in the normal
part of the curve. But, owing to the destructive effect acting
during the time that the temperature is T°, the observed
velocity at the end of the time will be V1,., which is less than
VT.
The ratio ryr will be related to the amount of destruction.
vT
Let the temperature be now suddenly lowered again to io° C.
The amount of the destruction is unchanged so that before
recovery the velocity will be V\o, which is less than V10, such
that fTT-is also related to the amount of destruction. We have
v
10
seen (fig. 2, points 16 and 17) that the velocity of a partially
recovered Amoeba varies with the temperature as it does in
the normal Amoeba, only on a proportionately lower scale.
Hence both - ^
and —• are related to the same amount of
V T
V
10
destruction in the same way.
V1
VT = ^ j i x V10 (all three of which can be observed).
v
10
This equation should allow us to extrapolate the normal part
of the velocity: temperature curve.
Unfortunately certain experimental difficulties render VT
difficult to estimate with accuracy. The velocity V10 should be
measured immediately the temperature is reduced to io°. But
it is found that the velocity does not reach its minimum
value until a few minutes after the temperature has fallen.
This effect, though perhaps partly instrumental, is probably
due to the relatively slow rate at which certain factors {e.g.
viscosity) fall to the normal value for the temperature. However,
the time required to reach the minimum is small compared with
the total period of recovery, and if V1^ be taken to be the
5*6
The Physiology of Amoeboid Movement
minimum velocity after cooling, the equation will still hold
approximately.
In order to find the mean value of VT for several experiments, the velocities should all be reduced proportionally so
that the velocity at io° C , (Vi0), is i.o. The relative value of
VT is then given:—
Relative VT = ^ L
i.o.
* 10
Table II. gives the mean value of VT for type B Amoebae
V1
from six determinations of ^— at three different temperatures.
V
TABLE I \.~Type B Amoebae.
Temperature raised
to T° for ten minutes.
Mean VT = ¥£-.
Range of Variation
* 10
v
10
T = 17-9 "C.
176
1-32 to 2-08
20-1
2-OI
i-55 » 2-95
21-6
2-7
i-5
.. 3-2
The range of variation is very great, so that the values
be considered to be very accurate ; but the results when
(fig 3, points A, B, C) do indicate that, were it not
destructive effect of the high temperature, the normal
velocity with temperature would continue.
cannot
plotted
for the
rise of
5. Experiments with Type A Amoebae.
The relation of velocity to temperature was determined for
type A Amoebae. Fig. 4 shows a mean curve obtained from
five different Amoebae.
This Amoeba moves much more irregularly than type B,
especially at temperatures above 180 C , when fresh pseudopodia
are continually thrown out. The curve is therefore not of the
same order of accuracy as that of type B, but it shows that
temperature affects these two very different Amoebae in a
similar manner. The range of activity of type A Amoebae
extends both above and below the range of type B.
S27
C. F. A. Pantin
d The Velocity at Normal Temperatures.
Fig. 3 shows that the velocity of a type B Amoeba is
almost a linear function of the centigrade temperature. This
recalls the observation of Knowlton and Starling 10 that the
3-0
VEL.at IO£
2-0
20
30°C
FIG. 4.—The relation to temperature of ciliary activity (from Gray), and of velocity of type A
and type B Amoebae. All three curves reduced to scale (velocity at i o ° = i-o).
variation of the rate of beat with temperature in the mammalian
heart is almost linear below the optimum.
In the case of the heart, Clark 8 has since shown that the
variation of rate increases more rapidly with the temperature
than a linear function. This is also true of amoeboid movement;
the velocity increases rather more rapidly for each successive
temperature interval.
5*8
The Physiology of Amoeboid Movement
The apparent straightness of the curve is probably only
due to the short range of temperature over which it extends.
The variation with temperature is really closely similar to that
of many other biological processes. Fig. 4 shows the mean
curves for type A and type B Amoebae plotted on the same
scale as the curve obtained by Gray* for the mechanical activity
of cilia. The similarity is brought out more strongly by
Table III., which gives the mean observed velocities for
type B Amoebae and the temperature coefficients calculated
from them by interpolation : except near o°C. the temperature
coefficients agree well with those for ciliary activity.
TABLE III.—Type B Amoebae.
Velocities reduced proportionally to the Value i-oo at 10° C.
Mean Temp.
Mean Vd.
- 3 - i ° C.
-i-9
0-00
O-OI
o-o
+ 2-5
4.9
7-6
9.9
12.6
013
032
0'53
0-77
0-96
Mean Temp.
I-2I
* Extrapolated value.
15-1° C.
17-4
20-2
22-O
23-O
.24-2
257
20-0*
Mean VeL
1-48
1-68
177
1-57
0-82
o-3S
o-oo
2-1
Interpolated Temperature
Coefficients.
Temp.
0 to 5
5 .. !°
10 „ 15
15 „ 2O*
Amoeba
Qio.
I6'9
3'i9
2-31
2-04
Cilia t
Qio.
3-52
3-oo
2-37
2-25
t Calculated from Gray's figures.0
It cannot be concluded at once that temperature affects the
mechanism of amoeboid activity in the same way as most other
biological processes, and that since the temperature coefficient
lies between 2 and 3, that the activity is controlled by a
chemical reaction.
Apart from the criticisms of the validity of applying Van't
Hoffs law given by Krogh,11 Lucas,18 and others,10'1 it is not
permissible to argue that because the velocity has a temperature
coefficient of the value required by this law, that amoeboid
activity depends upon a simple chemical reaction.
If any
biological process varies with the temperature, all the implications of this variation must be considered.
We must
therefore determine what relations the activity might have to
the velocity.
VOL. 1.—NO. 4.
529
C. F. A. Pantin
7. The Rate of doing Work.
A possible way in which amoeboid activity might be
conceived to occur would be by means of some chemical
reaction which directly supplied the energy necessary for the
activity. The rate at which the Amoeba did work would
then be proportional to the velocity of the chemical reaction—
provided the efficiency was constant. In this case it is not the
effect of temperature on the velocity, but on the rate of doing
work, with which the effect of temperature on other biological
processes must be compared.
Part of the work done by an Amoeba will be external and
part internal. It has been shown15 that continuous movement
of a limax Amoeba is effected by the streaming of the fluid
endoplasm forward through a tube of ectoplasm. The rate
at which internal work is done is therefore approximately
proportional to the speed of streaming of the endoplasm
multiplied by the resistance.
But the resistance itself varies directly as the speed of
streaming, v, and as the viscosity, n, so that:—
Rate of doing internal work =z/V
And since the velocity of progression, V, must be
proportional to the speed of the endoplasmic stream :—
Rate of doing internal work °=V\*
Compared with the internal work, the external work is
probably negligible. The method of locomotion of a limax
Amoeba is such that frictional resistance is minimal. Moreover,
the velocity of an Amoeba to which large pieces of debris
become attached remains unchanged, although the resistance,
and therefore the external work, must be greatly increased.
But viscosity is the factor which makes it almost certain
that the internal work completely outweighs the external. For
the endoplasm is a viscous fluid flowing through a tube of very
narrow bore, and—a fact perhaps not generally realised—the
absolute viscosity of even "fluid" protoplasm is enormous
compared with that of water.
* This general formula also holds for " rolling " Amoebae, e.g. A. verrucosa.
53°
The Physiology of Amoeboid Movement
A simple experiment illustrates this. A very little vaseline
is put on the bottom of a small dish filled with water. With
a fine pipette a few small Amoebae are placed by the side
of the vaseline, so that they may be examined together by a
f-in. objective. If the vaseline is teazed with a needle it will
be seen that, under the microscope, it appears to be quite fluid :
a thread of thickness comparable to that of an Amoeba if pulled
out rapidly rounds off into droplets. If the protoplasm of the
Amoebae is teazed in the same way, the impression is gained
that the viscosity of the more fluid Amoebae {e.g. type A) is
of the same order as that of vaseline, whereas the viscosity of
the more solid Amoebae {e.g. type B) is much greater. It
must be remembered that the protoplasm is bounded by a
more solid ectoplasm (Seifriz18 and others), but even allowing
for this it is difficult to avoid the conclusion that the protoplasm
of the more solid Amoebae is at least as viscous as vaseline.
Again egg albumen is much more viscous than water,8 but
it appears to be far more fluid than vaseline although solid
albumen is precipitated at the air interface.
A value for the viscosity of vaseline is not available to the
writer, but that of "Mobiloil BB," a heavy lubricating oil,
is 9.47 c.g.s. units at 20° C. compared with 0.0101 units for
water.6 Assuming vaseline to have a viscosity of this order,
we arrive at the conclusion that the absolute viscosity of
protoplasm may be at least 1000 times that of water. This is
corroborated by Seifriz's18 estimate that the viscosity of the
endoplasm of echinoderm eggs is of the same order as that of
concentrated glycerine {i.e. about 1500 times as viscous as
water at io° C ) .
For these reasons it is probable that almost the whole work
done during amoeboid activity is internal, and that therefore :—•
Rate of doing work
The velocity, V, is known, but we do not know the relative
viscosity, n- The viscosity varies with the temperature, and to
compare the rates of doing work at different temperatures we
must know this relative variation. On account of the practical
difficulties this cannot be determined directly for Amoeba, but
the writer determined the relative changes in viscosity for
C. F. A. Pantin
Nereis eggs,16 by Heilbrunn's method.8
are given in Table IV.
The relative values
TABLE IV.
Viscosity of Nereis
Temperature.
.
Relative viscosity.
.
.
—07°
1-95
Eggs.
10°
t-oo
20°
071
30°
057
Near oc C. the viscosity rises far more rapidly than it does
in the case of water. The protein solutions used by Chick*
show the same effect, the rise being more rapid with increasing
concentration of protein.
If we assume that the viscosity varies relatively with the
temperature in the protoplasm of Amoeba as it does in the
protoplasm of Nereis eggs, we can, by interpolation, find i.
Since we know the velocity, V2^ can be determined (Table V.).
TABLE v.
Temperature and the Rate of doing Work.
Temperature.
0-0° C.
4.9
9.9
15-1
20-0
Rate of doing Work
« vv
0-03
037
0-92
i-8o
3-14
Temperature.
o°
5
10
15
Qio
(by Interpolation).
to 5°
.. I O
„ 15
» 20
•39-3
60
3-6
3-1
The very high and variable temperature coefficient of the
rate of doing work does not resemble that found in most
biological processes. We are probably justified in concluding
that the rate of amoeboid activity does not depend directly
upon the velocity of some chemical reaction from which the
energy of activity is derived.
& The Rate of Change of State.
The movement of a limax Amoeba must now be re-examined
to determine what other factor might control the variation of
activity with temperature.
In the former paper16 it was shown that during continuous
locomotion the protoplasm of a limax Amoeba moves forward
53*
The Physiology of Amoeboid Movement
as the endoplasmic stream from the hind to the anterior end,
through the tube formed by the surrounding ectoplasm. The
endoplasmic stream turns outwards at the anterior end, and by
forming ectoplasm at the sides of this region, continuously adds
to the ectoplasmic tube. This tube is continuously undergoing
contraction as fast as it is formed, and is finally resorbed into
the endoplasmic stream at the hind end.
From this it is evident that during continuous amoeboid
movement any "element" of protoplasm undergoes a more or
less periodic change of state: it first moves forward as the
endoplasmic sol, then reaches the anterior end and is
incorporated in the ectoplasmic gel; it then moves towards the
hind end in the contracting ectoplasm and is finally resorbed
into the endoplasmic stream.
The velocity of locomotion of the Amoeba is directly related
to the time required for the complete period of this change of
state; for the velocity with which an "element" moves along
the endoplasmic stream, and the velocity with which it passes
towards the hind end in the contracting tube of ectoplasm are
both directly proportional to the velocity of locomotion.
It is possible to consider, therefore, that the controlling
factor in the velocity of amoeboid movement is the rate at which
the protoplasm can effect this change of state from sol
(endoplasm) to gel (ectoplasm), and vice versa.
It is not suggested that protoplasm consists of a large
number of "elements" each undergoing a rhythmic change,
sol^=gel, in a regular succession. It is merely pointed out
that in continuous amoeboid movement the protoplasm is
undergoing a periodic change of state ; that the rate at which
this change of state takes place is proportional to the velocity
of locomotion, and that the rate at which it can occur may be
the controlling factor in amoeboid activity.
The assumption that the rate of change of state is the
controlling factor in amoeboid activity gives a rational explanation of the fact that it is the variation of the velocity of an
Amoeba with temperature, and not that of the rate of doing
work, that runs parallel to the effect of temperature on other
biological processes.
This is clearly shown, in the case of ciliary activity in
533
C. F. A. Pantin
Table III., and also in Table VI. which gives the temperature
coefficients of some other processes for comparison.
T A B L E VI.
Q 10
„
„
„
„
„
velocity of Amoeba
.
.
.
.
rate of beat of frog's heart, 3
10
„
Terrapin heart,
„
Ceriodaphnia heart, 1 7
rate of conduction in nerve, 11
latent period of nerve,"
0° to 10°.
5° to 15°.
10° to S0°.
7-33
37
271
z-54
3-5
2-17
2-27
2-2
2-5
i-79
3-51
IO2
2-OI
3-34
The assumption also points to a possible explanation of the
high temperature coefficient near o° C. Near that temperature
the Amoeba becomes shorter and broader. The result is that
for a given rate of change of state the velocity is much lower
than if the animal were in the normal elongated form. Perhaps
this change of form is the result of a great rise in viscosity,
since the short broad form offers much less resistance to the
streaming endoplasm.
o. Discussion and Conclusion.
We have seen that the velocity of an Amoeba varies with
the temperature in a similar manner to many other biological
processes. The velocity is greatest at an optimum temperature
above which some part of the mechanism is progressively
destroyed. It is possible that this mechanism is of the nature
of an enzyme, though the optimum is low.
Were it not for this destruction, the velocity would continue
to rise with the temperature as it does below the optimum.
The rise in velocity with temperature is probably general for
all forms of amoeboid activity, for it has been shown to occur in
human leucocytes14 and to a certain extent in the leucocytes of
Limulus.12 It is also interesting to note that the velocity of
protoplasmic streaming appears to follow the same law, both in
the Myxomycetes and in plant cells (Kanitz, pp. 87-889).
At normal temperatures the temperature coefficient of the
velocity appears to be in accordance with Van't Hoffs law.
But examination of the mechanics of amoeboid movement
534
The Physiology of Amoeboid Movement
shows that if the effect of temperature were due directly to the
alteration of the velocity of a chemical reaction from which the
energy of amoeboid movement was derived, then the rate of
doing work and not the velocity of progression would vary as
the velocity of this reaction. But calculation of the rate of
doing work shows that its temperature coefficient is very high
and very variable, and unlike that found in most biological
processes.
On the other hand, the rate of change of state (soK^gel) in
the protoplasm is directly related to the velocity. If this is the
factor which determines the rate of amoeboid activity we at
once have an explanation of why the velocity of locomotion
should vary with the temperature in the same way as other
biological processes. This fact must be accounted for on any
hypothesis concerning the nature of the controlling process in
amoeboid activity.
From this it is argued that the velocity of continuous
amoeboid movement does not depend directly upon the velocity
of some chemical reaction supplying the necessary energy, but
that it probably does depend on the rate at which the protoplasm
can change its state. Temperature then affects the rate of this
change of state as it does the rate of most other biological
processes.
This does not preclude the possibility that the source of the
energy of amoeboid movement is ultimately a chemical reaction.
It is only implied that, if this is so, the rate of doing work
is not proportional to the velocity of this reaction. We are
therefore not dealing with the direct transformation of the
energy of a simple chemical reaction into work done by the
Amoeba. The rate of this transformation does not "set the
pace" of amoeboid activity.
The energy expended by an Amoeba in doing work may be
derived directly from the tension developed in the contracting
tube of ectoplasmic gel, perhaps also from the pressure of the
swelling protoplasm at the anterior end of the animal.16 If
the change of state (sol=?±:gel) of the protoplasm were itself
brought about by a chemical reaction, the rate of change of
state would depend on the velocity of the reaction. The rate
of amoeboid activity itself would then ultimately depend upon
535
C. F. A. Pantin
the velocity of the reaction, but only indirectly. The work
done by an Amoeba would be derived indirectly from the
chemical energy of the reaction by way of the potential energy
acquired by the protoplasm in changing its state. Therefore
there would be no reason to suppose that the rate of doing
work should bear any direct relation to the velocity of the
ultimate chemical reaction on which amoeboid activity
depended.
Finally we may inquire how far the temperature coefficient
of the velocity of amoeboid activity indicates that the change
of state in the protoplasm is itself brought about by a chemical
reaction.
Snyder 20 points out that the temperature coefficients of
chemical processes are not quite constant, and that Van't Hoff
suggested that they should be corrected for viscosity.
The writer has shown10 that if the temperature coefficients
of biological processes could be corrected for viscosity changes,
they would probably tend to become constant and of the magnitude characteristic of a chemical reaction. Moreover, correction
for changes in viscosity makes approximate allowance for those
very changes in the conditions of the protoplasm with temperature which have been considered to vitiate the comparison of
the rate of biological processes with chemical reactions.11' *• 18
It is therefore probable that the rate of amoeboid activity
is controlled by the rate at which protoplasm can change its
state, and the rate of this change of state is in turn possibly
controlled by a chemical reaction.
io. Summary.
1. The effect of temperature on the velocity of locomotion
of two species of marine limax Amoebae has been determined.
In both the velocity rises with the temperature. It is
reversibly inhibited just below o° C. There is a low optimum
temperature (type A, 22°C. to 250 C. ; type B, 20° C.) above
which the velocity falls rapidly ; at higher temperatures activity
is inhibited irreversibly.
2. Evidence is brought to show that the fall of velocity
above the optimum is due to a destructive effect on the
mechanism of amoeboid activity. It is shown that were this
536
The Physiology of Amoeboid Movement
effect absent, the velocity would probably continue to rise with
the temperature in a normal manner.
3. The temperature coefficient of the velocity is similar to
that of ciliary activity and many other biological processes.
4. The rate of amoeboid activity is probably not controlled
by the velocity of some simple chemical process the energy of
which is directly converted into work done, because the temperature coefficient of the rate of doing work is high and variable
and unlike that usually met with in biological processes.
5. The rate of amoeboid activity appears to be controlled by the rate at which the protoplasm changes its state
(sol ^2= gel). This provides a rational explanation of the fact
that it is the velocity and not the rate of doing work which
varies with the temperature as do other biological processes.
6. In view of conclusions arrived at in another paper,16 it
is possible that the value of the temperature coefficient indicates
that the rate at which protoplasm can change its state is controlled by a chemical reaction.
11. References.
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s
Chick, H., and Lubrzynska, E. (1914), "The Viscosity of Some Protein Solutions,"
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» Clark, A. J. (1920-21), "The Effect of Alterations of Temperature upon the
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4
Dixon, H. H. (1922), Practical Plant Biology, London.
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Goodwin, G., and others (1923), The Mechanical Properties of Fluids, Blackie
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• Gray, J. (1923), "The Mechanism of Ciliary Movement III.," Proc. Roy. Soc. B.,
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C. F. A. Pantin
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81
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538