CHAPTER XIVConclusions

Figure 45. Showing the path walked by a normal right-handed man (J. N.), blindfolded and counting his paces. The whole path was 546 paces long. The command given was to walk in the direction of the arrow until halted. The field was slightly rolling. The stump made necessary a termination of the experiment.

That a spiralizing mechanism is probably also present in organisms with highly developed equilibrating and orienting senses would be the logical expectation from what has been said regarding the presence of such a mechanism in the lower forms of life; but the effect of such a mechanism would naturally be suppressed when the orienting senses are functioning. To test this point, man was selected for experiment. With eyes blindfolded and ears plugged (this latter precaution was subsequently found to be unnecessary) so as to render the orienting senses ineffective, a normal man was directed to walk straight ahead over a large field towards an object he had just looked at. Although a number of experiments were made with several individuals,none of them was able to walk a straight path. All of them walked true spirals or series of circles with remarkably smooth curves(Figures45, 46). The spirals were right and left handed in the same individual, and sometimes in the same experiment. In these experiments the subject was totally unconscious of the direction in which he was walking. No effort of consciousness seemed capable of changing thedegree of curvatureof the spiral or circle and keep it smooth, though one could of course at any time break into the spiral or circle and walk off in another direction. (The writer himself walked in several experiments.) If one has one’s mindstronglyon the direction of walking, thinking of each step, the curve of the path shows small “wabbles”; but if one recites something or counts his paces, the curves are quite smooth.

Figure 46. Illustrating a path walked by a normal right-handed man (J. D.), blindfolded and counting his paces. The path was 560 paces long and was walked over the same field as the path illustrated in figure 45. The path had to be terminated because of a clump of brush.

Considerable unevenness of the ground has no effect on the curvature of the spiral. Structural differences in the legs are alsowithout effect, for a person with one artificial leg walks quite as smooth a spiral as one with two normal limbs.[7]

From these experiments on man, it follows that there is a “centre” in the central nervous system which automatically coördinates and controls movement during locomotion and, particularly from the point of view of this discussion, the direction of locomotion when the orienting senses are not functioning. This center must be very deep seated and automatic, and in so far as its influencing the direction of locomotion is concerned, it is of no discoverable use to man. It may be presumed to have existed before the present orienting senses originated in man, for there is very good evidence that horses and perhaps dogs, too, possess this mechanism. For these animals, like man, tend to walk in circles when lost, a peculiarity of behavior undoubtedly due to the activity of this mechanism and not to stronger right or left legs, etc., as has often been suggested (e. g., Thompson, ’17, p. 498). According to the accounts of experienced hunters, rabbits also run in circles when hard pressed by hounds, which may possibly be due to the suppression of the functioning of the orienting senses by fear, thus allowing the automatic directing mechanism to operate.

The facts are therefore that all organisms without orienting senses or equilibrating organs, or animals possessing such organs which are rendered ineffective by some means, will not move in straight paths nor in any kind of irregular path, butin orderly paths, so that a given segment of the path serves as a basis for predicting the further direction of the path. And the degree of accuracy to which such prediction may attain is proportional to the extent to which the activity of the automatic regulating mechanism may be kept free from outside interference. Theorganisms of which this holds true include, as far as known, all the free-swimming unicellulars, swarm spores of algae and fungi, uni-and multinucleate zoöspores, rotifers, a large number of worms and worm larvae of all classes (excepting the nematodes) and the larvae of many molluscs, echinoderms and copepods as well as some adult copepods. Organisms restricted to two dimensions of space in their movements, in which orderly paths have been recorded, are ameba and man and perhaps we may include the horse and the dog. This is indeed only a small number of organisms compared with all that can move; but there are representatives in the list of all the large groups excepting the higher plants, and without doubt observation will greatly extend the list, for there are mentioned here only such organisms whose movements have been definitely recorded or personally observed. As far as now known, no organism lacking orienting organs moves in a straight line. Many spermatozoa with flagellate tails seem, however, to do so, but no careful studies of their paths have yet been made.[8]

The orderliness of the paths of these organisms when moving under such conditions as described above, is itself orderly; that is, the path of all these organisms is a spiral of one kind or another: (1) a helical spiral, as in the free-swimming unicellulars; (2) a true spiral in one plane, as in man; (3) a helical spiral projected on a plane surface, as in ameba.

These facts point inevitably to the hypothesis that the movements of these and all other moving organisms are controlled by an automatic regulating mechanism, which is of essentiallysimilar nature in all organisms, as is indicated by the tendency to spiralize the path. This mechanism, being automatic, absolutely controls the direction of the path so long as outside interferences permit; but when sensory stimulation occurs, or when changes in temperature, etc. occur, the mechanism is no longer able to operate automatically or smoothly. The direction of the path then depends upon the nature and direction from which stimulation was received, and upon the degree and direction of change of temperature, etc.

The importance of this conception of movement lies in the fact that it enables us to look at a large mass of otherwise unrelated data from a single point of view. Secondly, it permits of a mathematical treatment of the whole subject of movement in organisms. And third, it replaces a teleological explanation of spiral movement in unicellulars, swarm spores, rotifers, etc., with a purely mechanistic explanation.

One of the most important results of recent work on the movements of ameba and of streaming endoplasm in plant cells is the rapidly growing conviction that the streaming of protoplasm, wherever it is found, is due to the same fundamental cause. The value of this conception lies in the greatly widened front that is presented for attacking the general problem of streaming. The many special aspects of streaming, which in the past have been thought to be essential or fundamental processes, may thus be placed against each other, following what is known as the comparative method, and the main problem will thus be freed of much that is not strictly relevant. In this way we come at once to the heart of the problem.

One of these special aspects of streaming in amebas is the formation of ectoplasm. For ectoplasm formation is not essential to streaming. But it is almost certainly essential to locomotion, for locomotion has not been observed in amebas where ectoplasm was not formed. But, on the other hand, ectoplasm, as known in the amebas, is not formed without streaming, although observations indicate that ectoplasm may suddenly and temporarily pass into the gel state (Vallisneria). Streaming is therefore the fundamental process in ameboid locomotion.

The surface layer of the ameba is physiologically distinct from the ectoplasm, although it differs from ectoplasm chiefly, if not wholly, by virtue of its position only. That is, the surface layer is a true surface tension film. There are no observations recorded which actually show that the surface film of the ameba is a semi-permeable or plasma membrane; but, on the other hand, there are no observations which speak against such a supposition. On theoretical grounds the conclusion is justifiable that the surface film as demonstrated by the movements of attached particles is the plasma membrane.

The similarity of the movements of the surface film in amebawith the movements of the superficial films ofOscillatoriafilaments, diatoms, crawling euglenas, and probably also Gregarinidas, indicates that the superficial films of all these organisms, including amebas, are all activated by surface tension changes. Thus instead of postulating several methods of locomotion which are fundamentally different from each other, for these respective organisms (excepting the ameba), one explanation serves the purpose; and it has the further merit of agreeing more nearly with observation than the various other theories proposed.

From the point of view of ameboid movement, the discovery of the surface film and its activities narrows down the problem very considerably. It does not helpdirectlyperhaps, in the solution of ameboid movement, but it shows clearly that the region where ectoplasm is most rapidly formed (at the anterior ends of pseudopods) is also the region where the superficial tension is increased. This therefore gives us somewhat of an insight into what must take place during the transformation of endoplasm into ectoplasm.

Although the wavy path of the ameba does not at present relate itself to any other process in the ameba, it is bound to be of the greatest significance in investigating the intimate nature of protoplasm while in movement. In so far as the wavy path concerns the ameba, it effectively disproves the presence of that scientific monstrosity, random movement. The path of the ameba is orderly.

The wavy path of the ameba represents a projection on a plane surface of a helical spiral. The path of the ameba is thus geometrically related to the spiral paths of free-swimming organisms such as ciliates, flagellates, rotifers, swarm spores, worm larvae, etc. But the paths are more closely related than merely geometrically. The effects produced by temperature on amebas and ciliates and flagellates indicate a relationship between the physical processes underlying the control of the direction of the paths traveled over in free movement. No causal distinction can yet be made between rotation on the long axis and the spiral swinging.

The spiral path is not an acquired habit. It is not a habit that has been developed to overcome asymmetry of body shape, forsome spirally swimming organisms are not asymmetrical enough to make swimming in spirals necessary. It is also unlikely that so many thousands of species of animals and plants of widely different groups would hit upon the same complex habit to solve widely different problems; for it is not equally important that all animals should swim in straight paths. It also necessitates supposing that the ancestors of our present ciliates, flagellates, rotifers, swarm spores, zoöspores, etc., were symmetrical and swam without revolving on the long axis and without forming spirals. Such an assumption is too formidable and makes the explanation top-heavy.

Spiral swimming is supposed to be due to an automatic regulating mechanism which is present in all moving organisms. It is held to be a spatial aspect of the physical processes originating and controlling movement. The property of moving automatically in an orderly path is inherent in organisms in the same way, e.g., as the property of growth is. A spiral path will be followed whenever an organism is free to move, that is, when not disturbed by sensory stimulation. Slight stimulation is often without effect. The justification of supposing that probably all moving organisms are within the grip of the spiral urge is found in the fact that the amebas, ciliates, flagellates, swarm spores, zoöspores, Oscillatoria, diatoms, rotifers, larvae of worms, molluscs and echinoderms, oligochaets, copepods, as well as man, all move in regular smooth spirals of one kind or another when free from strong stimulation, and that no organism that is free to move as these are, moves in a straight or irregular path.

The observations indicate that the same type of mechanism that controls the direction of the path of an organism also unifies and coördinates the streaming of the protoplasm of the ameba, the action of the cilia of the paramecium, or the contraction of the muscles of man, as the case may be. Why the automatic mechanism controlling the direction of movement should produce a helical spiral in paramecium, a wavy path or flattened spiral in ameba, and a series of spirals in man, is not yet subject to profitable discussion, except of course to point out that paramecium is not restricted to two dimensions of space as is ameba and man. In the nature of the case there can be no question but that themechanism is one that attaches to the fundamental structure of protoplasm rather than to the gross morphology. As a mathematical question, however, the circles occurring in the path of an ameba in low temperature may serve to connect up the flattened spiral path of the ameba under optimum conditions with the circular path often observed in man.

The movement of the ameba thus becomes related to crawling euglenas, Oscillatoria filaments, diatoms, and perhaps Gregarinidas, because of the movements of its surface layer; to leucocytes, streaming protoplasm in the higher plant cells, etc., because of its streaming endoplasm; and to the locomotory movements of all organisms because of the wavy character of its path, which betrays the activity of an automatic regulating mechanism, a type of which is held to be present in every moving organism.

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FOOTNOTES:[1]Wilson (’00) describes it asPelomyxa, but it has much closer affinities withAmoeba. It is in fact perhaps the closest relative ofAmoeba proteus. Ectoplasm formation, and especially the formation of ectoplasmic ridges incarolinensis, is exactly like that inproteus.[2]This is shown by the fact that after this ameba has taken on a spherical shape due to some disturbance in the water, the number of small ridgeless pseudopods thrown out upon resuming movement, is about the same as indubia; but after ridges begin to form, the number of pseudopods decreases.[3]That is, resemblances in nuclear division stages are not correlated with corresponding degrees of resemblance in somatic characters. It is not generally held that the shape or size or number of chromosomes is correlated with any external characters. It is the presence of hypothetical factors or genes which are held to be correlated with somatic characters and their number or arrangement in a chromosome is not in any way related to their character.[4]It is possible that Gruber was led to suggest a gelatinous composition for the layer in question on the strength of assertions made by several writers that amebas secrete mucus. It is true that amebas may be displaced by threads of mucus hanging to glass needles which has collected on the needles while manipulating the amebas in the culture medium, but that is not to be taken as evidence that the mucus is secreted by the amebas. Ameba cultures are always full of gelatinous material formed by bacteria. I have not thus far been able to convince myself that amebas actually secrete mucus.[5]According to Ewart (’03) the viscosity of streaming protoplasm in plant cells lies between η = .04 and η = .2. But the velocity of streaming endoplasm in ameba is considerably slower than that in the plant cells which formed the basis for Ewart’s calculations. In comparison, we may estimate the viscosity of the endoplasm of ameba as η = .1 dynes per sq. cm. The velocity of streaming endoplasm, as ascertained by observations onAmoeba dubia(in which the endoplasm flows usually rapidly) is1/880cm. per second.Now, given a unit mass of endoplasm moving at a given instant with a 1 velocity of1/880cm. per second against viscosity of η = .1 dynes per sq. how far will the unit mass travel before coming to rest?Force = Mass × Acceleration, and Acceleration = Velocity/Time.η = Viscosity = F = MA = MV/T.Now if M = 1, η = F = A = V/T.T = V/η =1/880/.1=1/88.The space travelled over in uniformly accelerated motion equalsS =1/2AT² =1/2×1/10× (1/88)² =1/154880= .00000645 cm.If, therefore, the force moving the central stream of endoplasm should suddenly be discontinued, the resistance offered by the viscosity of the enveloping endoplasm would allow it to move only .0000645 mm. before coming to rest. But the ameba as a whole moves more slowly than the central stream of endoplasm, the average rate of movement being about1/300mm. per second. The effect of the streaming endoplasm on the forward movement of the whole ameba would therefore be correspondingly decreased. Now if the ameba was perfectly homogeneous and perfectly symmetrical, and free from external stimulation, and moved in a perfectly homogeneous liquid on a perfectly plane surface, the excessively small amount of mechanical inertia would then be sufficient, theoretically, to cause the ameba to move in a straight instead of an irregular path. But these conditions are never realized. The ameba is unsymmetrical in form, heterogeneous in composition and always unsymmetrically stimulated; hence it is impossible that the excessively small amount of mechanical inertia can be considered a factor in determining the direction of the ameba’s path.[6]The gap between the rate of movement of a pseudopod and that of a flagellum is however very wide. Insofar as thecharacterof the movement is concerned, pseudopods such as those offlagellipodia, probably resemble the flagella of the soil ameba and of flagellates. But the very much greater speed of contraction of a flagellum and the presence of a special organ (blepharoplast) at the base of the flagellum, and their connection with the nucleus, indicates that a special mechanism is necessary to cause the rapid contraction. A flagellum appears to be a pseudopod supplied with something like nerve tissue and a ganglion capable of setting free a rapid succession of impulses.[7]It should be added here that since this paragraph was written I have been very fortunate to secure numerous records of paths swam by blindfolded swimmers, which strikingly resemble those of persons walking blindfolded as described above. Most of the common swimming strokes were employed in these observations and occasionally several strokes were employed in a single experiment. In a few cases the spiral path was made up of over twenty turns, and in one case of over fifty turns. A fuller discussion of these results does not seem pertinent here, and must be deferred to a later date.[8]Since this was written I have been able to examine the movement of live sperm cells in a number of representative animals, including the jellyfishAurelia; the molluscsOstrea,Solemya,Pandora; the arthropodsLimulusandAnisolabia, and the vertebrates frog, turtle, snake, cat, dog and man, with the result that all these spermatozoa revolve on their long axes and swim in spiral paths resembling those of flagellates. Owing to their minute size their movements are made out only with great difficulty, but so far as could be determined all the sperms of any one species turn on their axes in the same way, that is, either right-handed or left-handed. Recently there has also come to my notice the very informing paper of W. D. Hoyt, 1910, in theBotanical Gazette, in which it is stated that fern sperms of various species swim in spiral paths.

FOOTNOTES:

[1]Wilson (’00) describes it asPelomyxa, but it has much closer affinities withAmoeba. It is in fact perhaps the closest relative ofAmoeba proteus. Ectoplasm formation, and especially the formation of ectoplasmic ridges incarolinensis, is exactly like that inproteus.

[2]This is shown by the fact that after this ameba has taken on a spherical shape due to some disturbance in the water, the number of small ridgeless pseudopods thrown out upon resuming movement, is about the same as indubia; but after ridges begin to form, the number of pseudopods decreases.

[3]That is, resemblances in nuclear division stages are not correlated with corresponding degrees of resemblance in somatic characters. It is not generally held that the shape or size or number of chromosomes is correlated with any external characters. It is the presence of hypothetical factors or genes which are held to be correlated with somatic characters and their number or arrangement in a chromosome is not in any way related to their character.

[4]It is possible that Gruber was led to suggest a gelatinous composition for the layer in question on the strength of assertions made by several writers that amebas secrete mucus. It is true that amebas may be displaced by threads of mucus hanging to glass needles which has collected on the needles while manipulating the amebas in the culture medium, but that is not to be taken as evidence that the mucus is secreted by the amebas. Ameba cultures are always full of gelatinous material formed by bacteria. I have not thus far been able to convince myself that amebas actually secrete mucus.

[5]According to Ewart (’03) the viscosity of streaming protoplasm in plant cells lies between η = .04 and η = .2. But the velocity of streaming endoplasm in ameba is considerably slower than that in the plant cells which formed the basis for Ewart’s calculations. In comparison, we may estimate the viscosity of the endoplasm of ameba as η = .1 dynes per sq. cm. The velocity of streaming endoplasm, as ascertained by observations onAmoeba dubia(in which the endoplasm flows usually rapidly) is1/880cm. per second.Now, given a unit mass of endoplasm moving at a given instant with a 1 velocity of1/880cm. per second against viscosity of η = .1 dynes per sq. how far will the unit mass travel before coming to rest?Force = Mass × Acceleration, and Acceleration = Velocity/Time.η = Viscosity = F = MA = MV/T.Now if M = 1, η = F = A = V/T.T = V/η =1/880/.1=1/88.The space travelled over in uniformly accelerated motion equalsS =1/2AT² =1/2×1/10× (1/88)² =1/154880= .00000645 cm.If, therefore, the force moving the central stream of endoplasm should suddenly be discontinued, the resistance offered by the viscosity of the enveloping endoplasm would allow it to move only .0000645 mm. before coming to rest. But the ameba as a whole moves more slowly than the central stream of endoplasm, the average rate of movement being about1/300mm. per second. The effect of the streaming endoplasm on the forward movement of the whole ameba would therefore be correspondingly decreased. Now if the ameba was perfectly homogeneous and perfectly symmetrical, and free from external stimulation, and moved in a perfectly homogeneous liquid on a perfectly plane surface, the excessively small amount of mechanical inertia would then be sufficient, theoretically, to cause the ameba to move in a straight instead of an irregular path. But these conditions are never realized. The ameba is unsymmetrical in form, heterogeneous in composition and always unsymmetrically stimulated; hence it is impossible that the excessively small amount of mechanical inertia can be considered a factor in determining the direction of the ameba’s path.

Now, given a unit mass of endoplasm moving at a given instant with a 1 velocity of1/880cm. per second against viscosity of η = .1 dynes per sq. how far will the unit mass travel before coming to rest?

Force = Mass × Acceleration, and Acceleration = Velocity/Time.

η = Viscosity = F = MA = MV/T.

Now if M = 1, η = F = A = V/T.

T = V/η =1/880/.1=1/88.

The space travelled over in uniformly accelerated motion equals

S =1/2AT² =1/2×1/10× (1/88)² =1/154880= .00000645 cm.

If, therefore, the force moving the central stream of endoplasm should suddenly be discontinued, the resistance offered by the viscosity of the enveloping endoplasm would allow it to move only .0000645 mm. before coming to rest. But the ameba as a whole moves more slowly than the central stream of endoplasm, the average rate of movement being about1/300mm. per second. The effect of the streaming endoplasm on the forward movement of the whole ameba would therefore be correspondingly decreased. Now if the ameba was perfectly homogeneous and perfectly symmetrical, and free from external stimulation, and moved in a perfectly homogeneous liquid on a perfectly plane surface, the excessively small amount of mechanical inertia would then be sufficient, theoretically, to cause the ameba to move in a straight instead of an irregular path. But these conditions are never realized. The ameba is unsymmetrical in form, heterogeneous in composition and always unsymmetrically stimulated; hence it is impossible that the excessively small amount of mechanical inertia can be considered a factor in determining the direction of the ameba’s path.

[6]The gap between the rate of movement of a pseudopod and that of a flagellum is however very wide. Insofar as thecharacterof the movement is concerned, pseudopods such as those offlagellipodia, probably resemble the flagella of the soil ameba and of flagellates. But the very much greater speed of contraction of a flagellum and the presence of a special organ (blepharoplast) at the base of the flagellum, and their connection with the nucleus, indicates that a special mechanism is necessary to cause the rapid contraction. A flagellum appears to be a pseudopod supplied with something like nerve tissue and a ganglion capable of setting free a rapid succession of impulses.

[7]It should be added here that since this paragraph was written I have been very fortunate to secure numerous records of paths swam by blindfolded swimmers, which strikingly resemble those of persons walking blindfolded as described above. Most of the common swimming strokes were employed in these observations and occasionally several strokes were employed in a single experiment. In a few cases the spiral path was made up of over twenty turns, and in one case of over fifty turns. A fuller discussion of these results does not seem pertinent here, and must be deferred to a later date.

[8]Since this was written I have been able to examine the movement of live sperm cells in a number of representative animals, including the jellyfishAurelia; the molluscsOstrea,Solemya,Pandora; the arthropodsLimulusandAnisolabia, and the vertebrates frog, turtle, snake, cat, dog and man, with the result that all these spermatozoa revolve on their long axes and swim in spiral paths resembling those of flagellates. Owing to their minute size their movements are made out only with great difficulty, but so far as could be determined all the sperms of any one species turn on their axes in the same way, that is, either right-handed or left-handed. Recently there has also come to my notice the very informing paper of W. D. Hoyt, 1910, in theBotanical Gazette, in which it is stated that fern sperms of various species swim in spiral paths.

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