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 Distaso[3] summarize the various opinions with regard to the nucleus in bacteria as follows: