Chatterjee, B. R. (Baylor University College of Medicine, Houston, Texas) and Robert P. Williams. Cytological changes in aging bacterial cultures. J. Bacteriol. 84:340-344. 1962.-Morphological changes occurring in aging broth and agar cultures of Bacillus anthracis were observed with the phase-contrast microscope. In 4 to 5 days, in liquid culture, cells lost their normal shape and become fusiform or spherical. Chromatin bodies were clearly visible inside the cells at this time. Spontaneous conversion into protoplast-like, spherical cells was observed on the 6th or 7th day. These cells were sensitive to osmotic changes, but could be preserved by the addition of sucrose to the medium. Budding and atypical multicellular forms also were observed at this stage. In agar cultures, the conversion into spherical forms was observed with more regularity; the presence of sucrose in the medium favored the process. In very late stages of growth, the spherical cells disintegrated into conglomerated masses of cellular debris with the discrete chromatin bodies enmeshed in them. At this stage, secondary colonies appeared, superimposed on the primary ones, and on transfer to suitable medium gave rise to unstable L colonies.