The Fundamentals of Bacteriology. Charles Bradfield Morrey
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Fig. 10.—A thread of bacteria. Compare with Figs. 8 and 9.
Fig. 11.—A chain of spherical blue-green algæ.
Fig. 12.—A chain of spherical bacteria.
Fig. 13.—A pair of spherical blue-green algæ.
Further the chemical composition of bacteria is more like that of other fungous plants than of any of the forms classed as animals.
Fig. 14.—Spherical bacteria. Several pairs are shown.
Fig. 15.—Yeast cells. Some show typical budding.
The food of bacteria is always taken up in solution by diffusion through the outer covering of the cell as it is in all plants. Plant cells never surround and engulf particles of solid food and digest them within the cell as many single-celled animals do, and as the leukocytes and similar ameboid cells in practically all multicelled animals do.2
Fig. 16.—A portion of the mycelium of a mold. Note the large size and the branching.
One of the most marked differences between animals and plants is with respect to their energy relationships. Plants are characteristically storers of energy while animals are liberators of it. Some bacteria which have the power of swimming in a liquid certainly liberate relatively large amounts of energy, and in the changes which bacteria bring about in the material which they use as food considerable heat is evolved (“heating” of manure, etc.). Nevertheless the evidence is good that the bacteria as a class store much more of the energy contained in the substances actually taken into the body cell as food than is liberated in any form.
Bacteria do show some resemblance to the protozoa, or single-celled animal forms, in that the individuals of each group consist of one cell only and some bacteria have the power of independent motion from place to place in a liquid as most “infusoria” do, but here the resemblance ceases.
Bacteria are among the smallest of organisms, so small that it requires the highest powers of the microscope for their successful study, and the use of a special unit for their measurement. This unit is the one-thousandth part of a millimeter and is called the micro-millimeter or micron. Its symbol is the Greek letter mu (µ).
The size varies widely among different kinds but is fairly constant in the same kind. The smallest described form is said to be only 0.18µ long by 0.06µ thick and is just visible with the highest power of the microscope, though it is possible and even probable that there are forms still smaller which cannot be seen. Some large rare forms may measure 40µ in length, but the vast majority are from 1µ to 4µ or 5µ long, and from one-third to one-half as wide.
From the above description a bacterium might be said to be a microscopic, unicellular plant, without chlorophyl, which reproduces by dividing transversely.
PART I.
MORPHOLOGY
CHAPTER II.
CELL STRUCTURES.
The essential structures which may by appropriate means be distinguished in the bacterial cell are cell wall and cell contents, technically termed protoplasm, cytoplasm. The cell wall is not so dense, relatively, as that of green plants, but is thicker than the outer covering of protozoa. It is very similar to the cell wall of other lower fungi. Diffusion takes place readily through it with very little selective action on substances absorbed as judged by the comparative composition of bacteria and their surrounding medium.
Cytoplasm.—The cytoplasm according to Bütschli and others is somewhat different and slightly denser in its outer portion next to the cell wall. This layer is designated the ectoplasm, as distinguished from the remainder of the cell contents, the endoplasm. When bacteria are suddenly transferred from a given medium into one of decidedly greater density, there sometimes results a contraction of the endoplasm, due to the rapid diffusion of water. This phenomenon is designated plasmolysis (Fig. 17), and is similar to what occurs in the cells of higher plants when subjected to the same treatment. This is one of the methods which may be used to show the different parts of the cell just described.
If bacteria are suddenly transferred from a relatively dense medium to one which is of decidedly less density, it occasionally happens that water diffuses into the cell and swells up the endoplasm so much more rapidly than the cell wall that the latter ruptures and some of the endoplasm exudes in the form of droplets on the surface of the cell wall. This phenomenon is called plasmoptysis. Students will seldom observe the distinction between cell wall and cell contents, except that in examining living bacteria the outer portion appears more highly refractive. This is chiefly due to the presence of a cell wall, but is not a proof of its existence.
Fig. 17.—Cells of bacteria showing plasmolysis. The cell substance of three of the cells in the middle of the chain has shrunk until it appears as a round black mass. The cell wall shows as the lighter area.
Fig. 18.—Vacuoles in the bacterial cell. The lighter areas are vacuoles.
Nucleus.—Douglas and Distaso3 summarize the various opinions with regard to the nucleus in bacteria as follows:
1. Those who do not admit, the presence of a nucleus or of anything equivalent to it. (Fischer, Migula, Massart).
2. Those who consider that the entire bacterial cell is the equivalent of a nucleus and contains no protoplasm. (Ruzicka).
3. Those who admit the presence of nuclein but say that this is not morphologically differentiated from the protoplasm as a nucleus. (Weigert).
4. Those who consider the bacterial protoplasm to consist of a central endoplasm throughout which the nuclein is diffused and an external layer of ectoplasm next to the cell wall. (Bütschli, Zettnow).
5. Those who say that the bacterial cell contains a distinct nucleus, at least in most instances. These authors base their claims on staining with a Giemsa stain. (Feinberg, Ziemann, Neuvel, Dobell, Douglass and Distaso).
That nucleoproteins are present in the bacterial cell in relatively large amounts is well established. Also that there are other proteins and that the protoplasm is not all nuclein.
Some workers as noted above have been able to demonstrate collections of nuclein by staining, especially in very young cells. In older cells this material is in most instances diffused throughout the protoplasm and can not be so differentiated.
The following statement probably represents the generally accepted view at the present time:
A nucleus as such is not present in bacterial