Fixation and Staining of the Bacterial Nucleus

An examination of some early methods in bacterial cytology shows that technics for demonstrating the nucleus of the Eubacteriales were available for at least twenty years before the current era of investigation, which began in 1942. Although the bacterial nucleus reacts in many respects like the chromatin elements of higher plants, it shows certain peculiarities in its staining reactions. For example, hematoxylin, methyl green, and several preparations used to stain chromosomes, apparently do not exhibit the same affinity for the bacterial nucleus that they do for chromosomes in higher plants. Not only is the selection of a fixative important in nuclear studies, but also the manner in which the fixation is obtained. For example, when bacteria are fixed and processed in a completely wet state it is generally impossible to stain their nuclei. None of the special fixatives studied revealed any unusual organization in the bacterial cell or exhibited any advantage over the fixatives now in common use by bacteriologists. In view of the properties of osmium tetroxide vapor, particularly its relative lack of interference with positive nuclear staining, there can be little doubt of its superiority as a nuclear fixative. It appears that the basophilic material removed from the bacterial cell by hydrochloric acid is not only in the cytoplasm, but that a very significant amount of it is in close contact with the cell wall.