ON THE PHYSIOLOGY OF AMOEBOIDMOVEMENT.*

I I . — T H E EFFECT 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 amoeboidactivity was affected by certain changes in the conditions ofthe medium in the same way as certain other forms of con-tractility. This suggested that some fundamental mechanismof contractility was similar in all these cases.

Like the majority of biological processes, contractility isaffected in a characteristic manner by temperature, and if therereally is a fundamental similarity between amoeboid and otherforms of contractility, the effect of temperature should besimilar in both cases.

i. Material, Methods, etc.

Marine Amoebae, obtained from the laboratory tanks, wereused for the experiments. A full description of the Amoebae,their habitat and mode of progression, has been given in aprevious paper.16 The Amoebae were of the " Umax " form, thatis, they progressed by the continuous protrusion of a singleanterior 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 movein a straight line. And if the conditions of the medium areconstant the velocity of an individual Amoeba is constant towithin from i per cent, to 5 per cent, for at least twenty-fourhours. This holds true even if the conditions of the mediumhave been varied and then brought back to the original state,provided the variation has not been great enough to damagethe organism.

• Received May 21st, 1924.

C. F. A. PantinIn 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 themicroscope that the lines appeared to be 25 M apart, and thevelocity was measured by timing the Amoeba over a givennumber of divisions with a stop-watch.

Harrington and Learning7 have stated that the conditionsof lighting affect certain Amoebae. A half-watt frosted electriclamp was therefore used as illuminant in all the experiments.

The temperature was controlled by means of a speciallyconstructed 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 ofwhich 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 innerchamber 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 astream of water at the desired temperature. A thermometerentering the chamber registered the temperature to TV C.Details of the construction of the warm stage are given infig. i.

Amoeboid activity is influenced by factors other thantemperature {e.g. PH): the medium employed was alwaysnatural sea water at a constant PH which varied in differentexperiments from PH 7.8 to PH 8.2.

2. The Relation of Velocity to Temperature.

The usual procedure adopted was to determine the velocityat about 15° C , and then to lower the temperature by successiveintervals to the critical point at which activity was inhibited.

520

The Physiology of Amoeboid MovementThe temperature was then raised by intervals until movementceased owing to the destructive effect of the high temperatureupon the protoplasm.

The velocity was measured five to ten minutes after eachchange of temperature to allow the Amoeba to becomeacclimatised to the new conditions. However, the velocityusually became constant in about one minute, unless thetemperature was close to either critical point at which allmovement ceased. Since the warm stage itself takes from ahalf to one minute to attain a constant temperature after eachchange, acclimatisation is probably rapid except near thecritical temperature.

The velocity of both kinds of Amoebae studied variesmarkedly with the temperature. Fig. 2 shows a typicalcurve obtained from a type B Amoeba. The experimentwas commenced at I5.2°C. ; the temperature was thenlowered successively (through points 2 to 6) to — 2.00 C,and then raised.

From just above o°C. to i5°C. the velocity is approximatelyproportional to the centigrade temperature. For this Amoebathere is a distinct " l ag" in the velocity obtained with a risingtemperature; that is, the velocity at 10° is higher if approachedfrom a high temperature than if approached from a low one.This " l ag" 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 , thoughdeath does not occur rapidly (within ten minutes) until 30° C.

These points are well shown in fig. 3, which shows themean curve obtained from experiments on ten Amoebae. Foreach Amoeba the velocities measured were reduced proportion-ally to the same scale so that the value at io°C. was approxi-mately 1.00. The mean velocity was then taken for each 2.5°rise in temperature.

Like the majority of biological processes, amoeboid activityis inhibited a few degrees below o° C. This inhibition is com-pletely reversible: even if the Amoeba has been kept for sometime at - 30 C, yet on raising the temperature, recovery takesplace within a few minutes and the Amoeba moves with the

5 "

C. F. A. Pantinspeed characteristic of the temperature, except in cases whichshow the slight " l ag" effect already described.

Again, as in other processes, the activity rises with thetemperature to an optimum, the position of which shows slight

a

0 20 30CFlG. 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 fallsrapidly 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 Movementoptimum the Amoeba moves rather irregularly and tends toform lateral pseudopodia : with this loss of the limax form, thevelocity is no longer so accurate a measure of the activity ofthe Amoeba.

However, the optimum for amoeboid activity is of the same

20° 30°C.FlG. 3.—Mean variation of velocity with temperature for 10 type B Amoebae. Velocity reduced

to scale (velocity at IO° = IJD).

A, B, and C are extrapolated values referred to in the text

character as the optima of other processes ; if the temperaturebe raised above it until activity is inhibited we find that theinhibition is only partially reversible, as in other processes{e.g. ciliary activity6). Type B Amoebae were found to requireseveral hours to recover after inhibition at a temperature abovethe optimum, and type A Amoebae rarely, if ever, recoveredafter complete inhibition by heat.

5*3

C. F. A. PantinThe 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 casesof amoeboid activity, because McCutcheon M has shown that theoptimum for human leucocytes occurs at 40° C , as might beexpected. Moreover, it seems probable that many freshwaterAmoebae can withstand temperatures actually above the death-point of these marine Amoebae.

3. The Fall in Velocity above the Optimum.

The occurrence of an optimum activity suggests that abovethis point destructive forces begin to act on the mechanism.Gray6 has suggested that the fall in ciliary activity above theoptimum temperature might be due to the destruction of anenzyme: the argument applies also to amoeboid activity,although in this case the optimum is very low.

The following experiments show definitely that the fall inamoeboid activity is due to the destruction of some mechanismin the protoplasm. The velocity of a type B Amoeba wasdetermined at 10° C.; the temperature was then suddenly raisedand maintained at a higher value for ten minutes ; at the endof this time the temperature was suddenly lowered again toio° C, and the velocity of the Amoeba measured at intervals.At first the velocity was below its initial value at io° C, butrecovery gradually took place. The times for recovery fordifferent temperatures are given in Table I. The values wereobtained successively with the same Amoeba.

TABLE 1.

Initial Velocity measured at 10° C.

Temperature changedto T° C. for ten minutes.

T = 15-3° C.17-6

[optimum) 20-021-920-521-322'5

Time required forrecovery at 10° C.

0 minutes

3-4 ,.20 „70 „20 „

32about 240 „

These experiments definitely show that high temperatures tendto destroy something necessary for amoeboid activity, and that

524

The Physiology of Amoeboid Movementthe amount of destruction increases very rapidly with thetemperature above the optimum. They also show that alimited amount of destruction has taken place before ever theoptimum is reached. In the experiment quoted the Amoebarequired three to four minutes to recover the normal velocityafter 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 ofsubstances which is rapidly destroyed near and above theoptimum temperature. If this substance is partially destroyedor is present in less than the normal amount, the velocity ofthe Amoeba is proportionately lower, though otherwise thebehaviour is normal. This is shown in fig. 2.

In that experiment, immediately after the Amoeba had beenparalysed by being heated to 26.30 C, the temperature waslowered to I5.8°C, and the Amoeba allowed to recover.Thirty minutes later it had only partially recovered and thevelocity was proportionately below the normal for thattemperature (point 16). On now raising the temperature therelative increase in velocity was about the same as in thenormal Amoeba (point 17), but the velocity was still below itsnormal value for this temperature. It might be said that theAmoeba was following the normal temperature curve on areduced scale, the reduction being proportional to the amountof the substance or structure that had yet to be re-formed byrecovery.

4. Extrapolation of the Velocity: Temperature Curve.

It has been shown that the fall in velocity above theoptimum is due simply to a destructive effect. In the absenceof this effect the velocity should continue to rise above theactual optimum in continuation of the lower, normal part of thevelocity : temperature curve.

If allowance could be made for the destructive effect we couldthus extrapolate the normal part of the velocity : temperaturecurve. This would be of great value because the limited rangeover which the normal curve extends makes it difficult to comparewith the temperature curves of other physiological processes.

VOL. 1.—NO. 4. 525 a M

C. F. A. PantinThe destructive effect may be allowed for approximately in

the following way. Assume that an Amoeba moves with avelocity, V10, at 10° C. Let the temperature be raised abovethe optimum to T° C. for a certain time. If there were nodestructive effect the velocity at T° would be VT, the velocityhaving continued to rise with the temperature as in the normalpart of the curve. But, owing to the destructive effect actingduring the time that the temperature is T°, the observedvelocity 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.v T

Let the temperature be now suddenly lowered again to io° C.The amount of the destruction is unchanged so that beforerecovery the velocity will be V\o, which is less than V10, suchthat 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 partiallyrecovered Amoeba varies with the temperature as it does inthe normal Amoeba, only on a proportionately lower scale.

Hence both - ^ and —• are related to the same amount ofV 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 partof the velocity: temperature curve.

Unfortunately certain experimental difficulties render VT

difficult to estimate with accuracy. The velocity V10 should bemeasured immediately the temperature is reduced to io°. Butit is found that the velocity does not reach its minimumvalue until a few minutes after the temperature has fallen.This effect, though perhaps partly instrumental, is probablydue 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 withthe total period of recovery, and if V1^ be taken to be the

5*6

The Physiology of Amoeboid Movementminimum velocity after cooling, the equation will still holdapproximately.

In order to find the mean value of VT for several experi-ments, the velocities should all be reduced proportionally sothat the velocity at io° C , (Vi0), is i.o. The relative value ofVT is then given:—

Relative VT = ^ L* 10

i.o.

Table II. gives the mean value of VT for type B AmoebaeV1

from six determinations of ^— at three different temperatures.V

TABLE I \.~Type B Amoebae.

Temperature raisedto T° for ten minutes.

T = 17-9 "C.

20-1

21-6

Mean VT = ¥£-.* 10

176

2-OI

2-7

Range of Variation

v 10

1-32 to 2-08

i-55 » 2-95

i-5 .. 3-2

The range of variation is very great, so that the values cannotbe considered to be very accurate ; but the results when plotted(fig 3, points A, B, C) do indicate that, were it not for thedestructive effect of the high temperature, the normal rise ofvelocity with temperature would continue.

5. Experiments with Type A Amoebae.

The relation of velocity to temperature was determined fortype A Amoebae. Fig. 4 shows a mean curve obtained fromfive different Amoebae.

This Amoeba moves much more irregularly than type B,especially at temperatures above 180 C , when fresh pseudopodiaare continually thrown out. The curve is therefore not of thesame order of accuracy as that of type B, but it shows thattemperature affects these two very different Amoebae in asimilar manner. The range of activity of type A Amoebaeextends 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 isalmost a linear function of the centigrade temperature. Thisrecalls the observation of Knowlton and Starling10 that the

3-0

VEL.at IO£

2-0

20 30°CFIG. 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 mammalianheart is almost linear below the optimum.

In the case of the heart, Clark8 has since shown that thevariation of rate increases more rapidly with the temperaturethan a linear function. This is also true of amoeboid movement;the velocity increases rather more rapidly for each successivetemperature interval.

5*8

The Physiology of Amoeboid MovementThe 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 thatof many other biological processes. Fig. 4 shows the meancurves for type A and type B Amoebae plotted on the samescale as the curve obtained by Gray* for the mechanical activityof cilia. The similarity is brought out more strongly byTable III., which gives the mean observed velocities fortype B Amoebae and the temperature coefficients calculatedfrom them by interpolation : except near o°C. the temperaturecoefficients 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.

- 3 - i ° C.- i - 9

o-o+ 2-5

4.97-69.9

12.6

Mean Vd.

0-00O-OI0130320'530-770-96I - 2 I

Mean Temp.

15-1° C.17-420-222-O23-O

.24-225720-0*

Mean VeL

1-481-681771-570-82o-3So-oo2-1

Interpolated TemperatureCoefficients.

Temp.

0 to 55 .. !°

10 „ 1515 „ 2O*

AmoebaQio.

I6 '9

3'i92-312-04

Cilia tQio.

3-523-oo2-372-25

* Extrapolated value. t Calculated from Gray's figures.0

It cannot be concluded at once that temperature affects themechanism of amoeboid activity in the same way as most otherbiological processes, and that since the temperature coefficientlies between 2 and 3, that the activity is controlled by achemical reaction.

Apart from the criticisms of the validity of applying Van'tHoffs law given by Krogh,11 Lucas,18 and others,10'1 it is notpermissible to argue that because the velocity has a temperaturecoefficient of the value required by this law, that amoeboidactivity depends upon a simple chemical reaction. If anybiological process varies with the temperature, all the implica-tions of this variation must be considered. We musttherefore determine what relations the activity might have tothe 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 chemicalreaction which directly supplied the energy necessary for theactivity. The rate at which the Amoeba did work wouldthen be proportional to the velocity of the chemical reaction—provided the efficiency was constant. In this case it is not theeffect of temperature on the velocity, but on the rate of doingwork, with which the effect of temperature on other biologicalprocesses must be compared.

Part of the work done by an Amoeba will be external andpart internal. It has been shown15 that continuous movementof a limax Amoeba is effected by the streaming of the fluidendoplasm forward through a tube of ectoplasm. The rateat which internal work is done is therefore approximatelyproportional to the speed of streaming of the endoplasmmultiplied by the resistance.

But the resistance itself varies directly as the speed ofstreaming, v, and as the viscosity, n, so that:—

Rate of doing internal work =z/V

And since the velocity of progression, V, must beproportional to the speed of the endoplasmic stream :—

Rate of doing internal work °=V\*

Compared with the internal work, the external work isprobably negligible. The method of locomotion of a limaxAmoeba is such that frictional resistance is minimal. Moreover,the velocity of an Amoeba to which large pieces of debrisbecome attached remains unchanged, although the resistance,and therefore the external work, must be greatly increased.

But viscosity is the factor which makes it almost certainthat the internal work completely outweighs the external. Forthe endoplasm is a viscous fluid flowing through a tube of verynarrow bore, and—a fact perhaps not generally realised—theabsolute viscosity of even "fluid" protoplasm is enormouscompared with that of water.

* This general formula also holds for " rolling " Amoebae, e.g. A. verrucosa.53°

The Physiology of Amoeboid MovementA simple experiment illustrates this. A very little vaseline

is put on the bottom of a small dish filled with water. Witha fine pipette a few small Amoebae are placed by the sideof the vaseline, so that they may be examined together by af-in. objective. If the vaseline is teazed with a needle it willbe seen that, under the microscope, it appears to be quite fluid :a thread of thickness comparable to that of an Amoeba if pulledout rapidly rounds off into droplets. If the protoplasm of theAmoebae is teazed in the same way, the impression is gainedthat the viscosity of the more fluid Amoebae {e.g. type A) isof the same order as that of vaseline, whereas the viscosity ofthe more solid Amoebae {e.g. type B) is much greater. Itmust be remembered that the protoplasm is bounded by amore solid ectoplasm (Seifriz18 and others), but even allowingfor this it is difficult to avoid the conclusion that the protoplasmof the more solid Amoebae is at least as viscous as vaseline.Again egg albumen is much more viscous than water,8 butit appears to be far more fluid than vaseline although solidalbumen is precipitated at the air interface.

A value for the viscosity of vaseline is not available to thewriter, but that of "Mobiloil BB," a heavy lubricating oil,is 9.47 c.g.s. units at 20° C. compared with 0.0101 units forwater.6 Assuming vaseline to have a viscosity of this order,we arrive at the conclusion that the absolute viscosity ofprotoplasm may be at least 1000 times that of water. This iscorroborated by Seifriz's18 estimate that the viscosity of theendoplasm of echinoderm eggs is of the same order as that ofconcentrated glycerine {i.e. about 1500 times as viscous aswater at io° C) .

For these reasons it is probable that almost the whole workdone during amoeboid activity is internal, and that therefore :—•

Rate of doing work

The velocity, V, is known, but we do not know the relativeviscosity, n- The viscosity varies with the temperature, and tocompare the rates of doing work at different temperatures wemust know this relative variation. On account of the practicaldifficulties this cannot be determined directly for Amoeba, butthe writer determined the relative changes in viscosity for

C. F. A. PantinNereis eggs,16 by Heilbrunn's method.8

are given in Table IV.The relative values

TABLE IV.

Viscosity of Nereis Eggs.

Temperature. . . —07° 10°Relative viscosity. . 1-95 t-oo

20°071

30°057

Near oc C. the viscosity rises far more rapidly than it doesin the case of water. The protein solutions used by Chick*show the same effect, the rise being more rapid with increasingconcentration of protein.

If we assume that the viscosity varies relatively with thetemperature in the protoplasm of Amoeba as it does in theprotoplasm 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.4.99.9

15-120-0

Rate of doing Work

« vv

0-030370-92i-8o3-14

Temperature.

o° to 5°5 .. I O

10 „ 1515 » 20

Qio(by Interpolation).

•39-3603-63-1

The very high and variable temperature coefficient of therate of doing work does not resemble that found in mostbiological processes. We are probably justified in concludingthat the rate of amoeboid activity does not depend directlyupon the velocity of some chemical reaction from which theenergy of activity is derived.

& The Rate of Change of State.

The movement of a limax Amoeba must now be re-examinedto determine what other factor might control the variation ofactivity with temperature.

In the former paper16 it was shown that during continuouslocomotion the protoplasm of a limax Amoeba moves forward

53*

The Physiology of Amoeboid Movementas the endoplasmic stream from the hind to the anterior end,through the tube formed by the surrounding ectoplasm. Theendoplasmic stream turns outwards at the anterior end, and byforming ectoplasm at the sides of this region, continuously addsto the ectoplasmic tube. This tube is continuously undergoingcontraction as fast as it is formed, and is finally resorbed intothe endoplasmic stream at the hind end.

From this it is evident that during continuous amoeboidmovement any "element" of protoplasm undergoes a more orless periodic change of state: it first moves forward as theendoplasmic sol, then reaches the anterior end and isincorporated in the ectoplasmic gel; it then moves towards thehind end in the contracting ectoplasm and is finally resorbedinto the endoplasmic stream.

The velocity of locomotion of the Amoeba is directly relatedto the time required for the complete period of this change ofstate; for the velocity with which an "element" moves alongthe endoplasmic stream, and the velocity with which it passestowards the hind end in the contracting tube of ectoplasm areboth directly proportional to the velocity of locomotion.

It is possible to consider, therefore, that the controllingfactor in the velocity of amoeboid movement is the rate at whichthe 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 largenumber of "elements" each undergoing a rhythmic change,sol^=gel, in a regular succession. It is merely pointed outthat in continuous amoeboid movement the protoplasm isundergoing a periodic change of state ; that the rate at whichthis change of state takes place is proportional to the velocityof locomotion, and that the rate at which it can occur may bethe controlling factor in amoeboid activity.

The assumption that the rate of change of state is thecontrolling factor in amoeboid activity gives a rational explana-tion of the fact that it is the variation of the velocity of anAmoeba with temperature, and not that of the rate of doingwork, that runs parallel to the effect of temperature on otherbiological processes.

This is clearly shown, in the case of ciliary activity in533

C. F. A. PantinTable III., and also in Table VI. which gives the temperaturecoefficients of some other processes for comparison.

T A B L E

Q 10 velocity of Amoeba . . . .„ rate of beat of frog's heart,3

„ „ Terrapin heart,10

„ „ Ceriodaphnia heart,17

„ rate of conduction in nerve,11

„ latent period of nerve,"

VI.

0° to 10°.

7-3337

IO2

5° to 15°.

271z-543-5

2-OI

3-34

10° to S0°.

2-172-272-22-5i-793-51

The assumption also points to a possible explanation of thehigh temperature coefficient near o° C. Near that temperaturethe Amoeba becomes shorter and broader. The result is thatfor a given rate of change of state the velocity is much lowerthan if the animal were in the normal elongated form. Perhapsthis change of form is the result of a great rise in viscosity,since the short broad form offers much less resistance to thestreaming endoplasm.

o. Discussion and Conclusion.

We have seen that the velocity of an Amoeba varies withthe temperature in a similar manner to many other biologicalprocesses. The velocity is greatest at an optimum temperatureabove which some part of the mechanism is progressivelydestroyed. It is possible that this mechanism is of the natureof an enzyme, though the optimum is low.

Were it not for this destruction, the velocity would continueto rise with the temperature as it does below the optimum.The rise in velocity with temperature is probably general forall forms of amoeboid activity, for it has been shown to occur inhuman leucocytes14 and to a certain extent in the leucocytes ofLimulus.12 It is also interesting to note that the velocity ofprotoplasmic streaming appears to follow the same law, both inthe Myxomycetes and in plant cells (Kanitz, pp. 87-889).

At normal temperatures the temperature coefficient of thevelocity appears to be in accordance with Van't Hoffs law.But examination of the mechanics of amoeboid movement

534

The Physiology of Amoeboid Movementshows that if the effect of temperature were due directly to thealteration of the velocity of a chemical reaction from which theenergy of amoeboid movement was derived, then the rate ofdoing work and not the velocity of progression would vary asthe velocity of this reaction. But calculation of the rate ofdoing work shows that its temperature coefficient is very highand very variable, and unlike that found in most biologicalprocesses.

On the other hand, the rate of change of state (soK^gel) inthe protoplasm is directly related to the velocity. If this is thefactor which determines the rate of amoeboid activity we atonce have an explanation of why the velocity of locomotionshould vary with the temperature in the same way as otherbiological processes. This fact must be accounted for on anyhypothesis concerning the nature of the controlling process inamoeboid activity.

From this it is argued that the velocity of continuousamoeboid movement does not depend directly upon the velocityof some chemical reaction supplying the necessary energy, butthat it probably does depend on the rate at which the protoplasmcan change its state. Temperature then affects the rate of thischange of state as it does the rate of most other biologicalprocesses.

This does not preclude the possibility that the source of theenergy of amoeboid movement is ultimately a chemical reaction.It is only implied that, if this is so, the rate of doing workis not proportional to the velocity of this reaction. We aretherefore not dealing with the direct transformation of theenergy of a simple chemical reaction into work done by theAmoeba. The rate of this transformation does not "set thepace" of amoeboid activity.

The energy expended by an Amoeba in doing work may bederived directly from the tension developed in the contractingtube of ectoplasmic gel, perhaps also from the pressure of theswelling protoplasm at the anterior end of the animal.16 Ifthe change of state (sol=?±:gel) of the protoplasm were itselfbrought about by a chemical reaction, the rate of change ofstate would depend on the velocity of the reaction. The rateof amoeboid activity itself would then ultimately depend upon

535

C. F. A. Pantinthe velocity of the reaction, but only indirectly. The workdone by an Amoeba would be derived indirectly from thechemical energy of the reaction by way of the potential energyacquired by the protoplasm in changing its state. Thereforethere would be no reason to suppose that the rate of doingwork should bear any direct relation to the velocity of theultimate chemical reaction on which amoeboid activitydepended.

Finally we may inquire how far the temperature coefficientof the velocity of amoeboid activity indicates that the changeof state in the protoplasm is itself brought about by a chemicalreaction.

Snyder20 points out that the temperature coefficients ofchemical processes are not quite constant, and that Van't Hoffsuggested that they should be corrected for viscosity.

The writer has shown10 that if the temperature coefficientsof biological processes could be corrected for viscosity changes,they would probably tend to become constant and of the magni-tude characteristic of a chemical reaction. Moreover, correctionfor changes in viscosity makes approximate allowance for thosevery changes in the conditions of the protoplasm with tempera-ture which have been considered to vitiate the comparison ofthe rate of biological processes with chemical reactions.11' *• 18

It is therefore probable that the rate of amoeboid activityis controlled by the rate at which protoplasm can change itsstate, and the rate of this change of state is in turn possiblycontrolled 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 isreversibly inhibited just below o° C. There is a low optimumtemperature (type A, 22°C. to 250 C. ; type B, 20° C.) abovewhich the velocity falls rapidly ; at higher temperatures activityis inhibited irreversibly.

2. Evidence is brought to show that the fall of velocityabove the optimum is due to a destructive effect on themechanism of amoeboid activity. It is shown that were this

536

The Physiology of Amoeboid Movementeffect absent, the velocity would probably continue to rise withthe temperature in a normal manner.

3. The temperature coefficient of the velocity is similar tothat of ciliary activity and many other biological processes.

4. The rate of amoeboid activity is probably not controlledby the velocity of some simple chemical process the energy ofwhich is directly converted into work done, because the tempera-ture coefficient of the rate of doing work is high and variableand unlike that usually met with in biological processes.

5. The rate of amoeboid activity appears to be con-trolled by the rate at which the protoplasm changes its state(sol ̂ 2= gel). This provides a rational explanation of the factthat it is the velocity and not the rate of doing work whichvaries with the temperature as do other biological processes.

6. In view of conclusions arrived at in another paper,16 itis possible that the value of the temperature coefficient indicatesthat the rate at which protoplasm can change its state is con-trolled by a chemical reaction.

11. References.1 Adrian, E. D. (1914), " The Temperature Coefficient of the Refractory Period in

Nerve," Journ. Physiol., 48, 453.s Chick, H., and Lubrzynska, E. (1914), "The Viscosity of Some Protein Solutions,"

Biochem. Journ., 8, 59.» Clark, A. J. (1920-21), "The Effect of Alterations of Temperature upon the

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