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 cells, except in a few large rare forms and in very young cells. Nuclein, the characteristic chemical substance in nuclei, which when aggregated forms the nucleus, is scattered throughout the cell contents and thus intimately mingled with the protoplasm, and cannot be differentiated by staining as in most cells.
The close association of nuclein and protoplasm may explain the rapid rate of division of bacteria (Chapter VIII, [p. 91]).