A text book of physiology / by William Rutherford.

Date:: 1880

Credit: A text book of physiology / by William Rutherford. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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$toplasm. In the amoeba (Fig. 8) tlie protoplasm (2j) usually encloses a vesicular nucleus (n), and this in turn a granule termed a nucleolus («'). The protoplasm may have a uniform finely graimlar appearance, but in some cases its outer part is hyaline. There is usually no periplast, but sometimes this is produced by the protoplasm, and the amceba thus becomes encysted (D). A n r J) Fig. 7. A, Amceba. 1} C, undergoing division. D, quiescent amceba eueysted : s, envelope ; )|, protoplasm ; ii, nucleus, nucleolus, x about 400. (Hceckel.) Amoeboid Movement.—The protamcaba and the non-encysted amoeba constantly exhil)it in their normal condition a motion termed amcehoid. This is characterised by indefinite changes of shape due to a streaming motion of the i)rotoplasm. Protrusions of the j^rotoplasm {yseudopodia) occur at any part of the surface. These may afterwards be M'ithdrawn, or the general mass of the protoplasm may move towards them, and thus a locomotion of a part or of the whole of the amoeba ensue. Amoeboid movement is ascribed to contractility,—a property belonging to some forms of protoplasm and to some of its modifications, whereby its particles assume different relative positions, and tluis occasion an indefinite or definite change of shape in the mass ; thus, when a muscle contracts, the change of shape is always in a definite direction, but in amoeboid masses of pi'otoplasm the changes of shape are altogether indefinite. The study of amoeboid motion is very instructive, for it leads to the conviction that within a continuous protoplasmic imit, excitement may be partial or general. A shock of induced electricity sets up a general excite- ment, the amceba withdrawing its processes and becoming spheroidal. If the shock is not too powerful, the amoeba after a time again begins to crawl about, but with shocks of gi'eat intensity the contractile substance is paralysed. When the amceba comes into contact with solid particles, it throws out processes around them, and the particles are thus enveloped. It seems as if the protoplasm were locally excited by the contact of the particles, nevertheless, processes may be thrown out when the amosba is not in contact with any solid matter. Cold retards, while a moderate heat accelerates the motion—doubt- less by retarding or hastening the metabolism on which the mechanical movement immediately depends. On raising the temperatiu-e from 40° to 45° C. (104° to 113° F.) a permanent heat-stiffening ensues, owing to coagulation of the proteid matter of the protoplasm, and death is the result. Similar effects are produced by heat on the contractile substance of muscle. The movements of the amoeba must be regarded as resulting from chemical changes within the protoplasmic machinery. An appro-$

A text book of physiology / by William Rutherford.

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