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Some Observations on the Behaviour of Amoeba Proteus

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Some Observations on the Behaviour of Amoeba Proteus Some Observations on the Behaviour of Amoeba proteus. By C. W. Parsons, B.A., Department of Zoology, University of Glasgow. With 9 Text-figures. ALTHOUGH the body-form of Amoeba proteus shows so much diversity in any healthy culture, the differences that may be observed conform to certain types. If these are assembled, they fall into groups which may be supposed to indicate physiological variation in the organisms ; for they are then reacting in different ways to the stimuli provided by the same external medium, and such behaviour can best be explained on physiological bases. The investigation of the groups is approached in the following pages by two different routes. The first is experimental and consists in a re-examination of the normal behaviour of adult Amoebae in the aquarium medium in which they are best cultured (see Monica Taylor, 11), followed by an analysis of their reactions to simple changes in their environment. The second is deductive. It rests upon a hypothesis relating the degree of activity of these organisms, as measured by the rapidity and ease with which they extend their pseudopodia, with their health. It recognizes the presence of healthy forms, in unfavourable as well as in favourable environments, and puts forward the view that some Amoebae are more adaptable to change of medium than are others. A link is here established with the well-known fact that while the Amoebae in a culture cease to reproduce by fission after a time, many of them do not enter on the cycle of encystment. They die out for no obvious 630 C. W. PARSONS reason. Food remains abundant, overcrowding is avoided, and the pH throughout the culture may be adjusted to give condi- tions normally ideal for multiplication. The attempt is here made to correlate this peculiarity in life history with a con- spicuous variation in body-form, and the types exhibiting this variation are defined. Material.—Adult Amoebae having chromosome blocks in the periphery of their nuclei, from a nourishing sub-culture of Dr. Monica Taylor's culture ' 19 ', type ' B ' (12, pp. 187 and 120). Apparatus included — plunger pipettes, i.e. capillary pipettes fitted internally with drawn-glass rods and sealed with rubber tubing. (See Brooker Klugh, 5.) Solid watch-glasses, 1| in. square; J in. deep for supporting cover-slips in high-power work ; ^ in. deep for general purposes. Sarensen phosphate buffer solutions with indicators, made up to 10 e.c. and 2 c.c. A. Behaviour of Adult Amoebae in Culture Media free from Debris. pH 6-8. The Amoebae are readily seen as white specks if debris con- taining them is taken from the parent culture and placed in a shallow dish on a black background. They may be picked up singly with the plunger pipette and transferred for observa- tion to a solid watch-glass containing clean culture medium. If there is rather less than 2 c.c. of fluid they may be focussed with a Zeiss ' A ' objective (f in.), and their behaviour recorded by notes and drawings taken at suitable intervals. High-power observation of single living Amoebae in a drop of fluid was carried out on a clean glass cover-slip supported in the well of one of the very shallow watch-glasses (£ in. deep). If the drop of fluid is small, the Amoebae may be focussed with a Zeiss ' D ' objective (£ in.), and the drop can be renewed as required from a fine-drawn pipette. When set aside, rapid evaporation may be prevented by placing another solid watch- glass on top of the one already holding the cover-slip, and the Amoebae remain alive in the drop. BEHAVIOUR OF AMOEBA 631 When they are picked up with the plunger pipette the Amoebae withdraw their pseudopodia, and it thus comes about that they are delivered to the solid watch-glasses as rounded masses of protoplasm. If they are kept floating—by gentle agitation of the fluid—they extend numerous blunt pseudo- podia (Text-fig. 1). When allowed to settle, however, they adhere to the glass surface in an orderly fashion. First, one of the pseudopodia reaches the substratum and adheres to it by TEXT-FIGS. 1, 2. Tig. 1.—Typical body-form of a floating Amoeba proteusinits aquarium culture medium. The figure shows a radial disposition of pseudopodia of roughly equal size. Fig. 2.—Contact with the substratum is first established by adhesion to it of one of the radial pseudopodia, which is distinguishable now as the major pseudopodium. the tip. Then it receives the remaining protoplasm (Text- figs. 2, 3, and 4) and, leading the organism down to the sub- stratum, it becomes the directive pseudopodium in the new line of advance. The Amoebae adhere closely to the glass surface as a rule, and move rapidly over it in a digitate form. A broader extremity crowned with active pseudopodia lies in the main axis of advance, and a slight constriction commonly marks the ' tail' (Text-fig. 4, t). The ' tail ' is a conspicuous feature of most Amoebae even in experimental media. It is seldom the seat of pseudopodia 632 C. W. PARSONS formation, a point which is emphasized by observing the- effect of mechanical stimulation upon one of these adhering- forms in culture medium. Schaeffer has shown how they respond when a glass needle is agitated near to them by initiating the ' feeding mechanism' (10, p. 229), but if the medium is- disturbed in this way immediately in front of the advancing pseudopodia, an avoiding reaction is induced. The flow of TEXT-FIGS. 3, 4. Fig. 3.—Further stage in the transition from a floating condition to one of adherence to the substratum. Fig. 4.—A completely adherent active Amoeba of the type shown floating in Text-fig. 1, with a body-form frequently observed, comprising three main pseudopodia, an elongate body, and a slightly constricted ' tail' (t). Same scale as fig. 1. granules is at first arrested and then reversed. After receding' a little, the Amoeba moves away afresh at an angle less than a right angle from its previous direction of flow. If now left undisturbed the pseudopodia gradually deflect into the original alinement and draw the animal into a path parallel to but slightly removed from its former course. On the other hand, this movement may be checked soon after its commencement by disturbing the medium again in front of the pseudopodia when they begin to diverge. The original course is then BEHAVIOUR OF AMOEBA 638 reversed : not, however, by the formation of pseudopodia at the hinder end, but by movement of lateral pseudopodia into the new position which draw the ' tail' round after them. This behaviour is typical of the most active adult Amoebae in culture media. Many adult Amoebae prove to be relatively inactive when taken from the parent culture. They are frequently more consolidated than the more active forms and may be very much shrunken. There seems, in fact, to be a gradation between the most active and least active Amoebae, marked by a change in their appearance under transmitted light from grey to black. It is notable also that the darker forms tend to lose their adhesion to the sides of the vessel containing them with greater ease than do the active grey ones. This suggests that granu- larity and adhesiveness on the one hand, and readiness of movement on the other, may be complementary features. B. Behaviour of Amoeba proteus in Pure Media. The water used in the following observations was distilled once from Glasgow tap-water in a glass condensing apparatus. A little potassium permanganate and a trace of mineral acid was added before distillation to oxidize impurities. The distillate, called hereunder glass distilled Avater, had a steady pH of 5-8 before prolonged exposure to the atmosphere. The Amoebae may reasonably be separated into three types on the basis of their reactions to this medium. 1. The majority quickly extend numerous pseudopodia to relatively great distances. (Text-fig. 5.) The reaction is the same in well-aerated distilled water, and has no relation therefore to the recognized paucity of oxygen in untreated glass distilled water. On theoretical grounds Mr. C. F. A. Pantin informs me that the ratio of surface to volume in Amoeba is so great, that equilibration with oxygen in the external medium is effected in an extremely short space of time. The small increase of surface produced therefore by great extension of pseudopodia, will not avail to compensate for a law oxygen content in the medium; although of course the great variation in ' per- 634 C. W. PARSONS nieability ' of living protoplasm to oxygen is not disputed (cf. ' Air-bladder of Fishes '). TEXT-FIG. 5. The exaggerated floating Jorm ot an active Amoeba suspended in distilled water. The attenuated pseudopodia suggested the dis- tinction of Amoebae that react in this way from others which are less active, and it was convenient to describe them as type ' A ' Amoebae. Amoebae in glass distilled water do not, as a rule, fix them- selves to the substratum. They float with extended pseudo- podia in a most grotesque manner, and are extremely active BEHAVIOUR OF AMOEBA 685 at first. Their energy is slowly dissipated, however, and in 8-10 hours they become sluggish. As time elapses they shrink and grow darker in appearance, but they may remain alive 5-7 days before cytolysis. The death of the organism is fre- quently preceded by its assumption of a more or less spherical form in accordance with its subjection to the ordinary forces of surface tension. Distension of its outer layers—owing to the decrease in efficiency of the contractile vacuole which normally Illustrates a body-form not infrequently observed amongst active Amoebae that are floating in pure media.
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