The interpretation of appearances in the cytological staining of bacteria

Abstract

BECAUSE of their small size, and because their reactions to standard staining and fixation techniques are often entirely different from those of plant and animal cells, the interpretation of cytological appearances in bacteria is an exceedingly difficult and specialised task, and frequently causes misconception and confusion. In many bacteria the cytoplasm stains very deeply with “nuclear” dyes, and sometimes may cause the nuclear structures to appear lightly stained against a dark background, where they are not entirely concealed. The HCl hydrolysis technique of Piekarski (12) was introduced with the purpose of avoiding this difficulty, and has been employed with considerable success by many workers. A second important point in the study of bacterial cytology is the difficulty of demonstrating the cell wall without the use of mordants. Many species of bacteria are subdivided into small cells by crosswalls derived from the cell wall, and these crosswalls are secreted by cytoplasmic septa containing an element which stains with basic dyes. Thus in preparations stained by simple cytological methods, the multicellular structure of the bacillus is not apparent, whereas the interpretation of the nuclear structures is complicated by material, of similar staining reaction, derived from the cell envelopes. This problem was well explained by Robinow (13), but many conscientious studies have since been rendered valueless because the authors, unaware of, or choosing to ignore the structure of the cell envelopes, have interpreted complex multicellular bacteria as single cells. This applies, for example, to the studies of Knaysi, Hillier and Fabricant (9) upon Mycobacterizzm tuberculosis and to a paper, which recently appeared in this Journal, by DeLamater and Mudd (5). In the latter paper, the authors interpreted various appearances in Bacillus megatherium as classical mitotic figures. They were, in the opinion of the present writer, caused by the effect of unsuitable fixation methods upon this organism, which DeLamater and Mudd apparently believed to consist of multinucleate cells, whereas, in fact, each of their