1953b Spore structure as revealed by thin sections

The cytological study of fully developed rest-ing spores of bacteria is rendered difficult by their extreme refractility. Acid hydrolysis makes spores transparent and stainable and has been valued as an effective means of demonstrating the nuclear material of these cells. Lately, how-ever, it has come under suspicion of causing serious disarrangement of the spore contents (Bisset and Hale, 1951; Preuner, 1951). Direct information on the internal configuration of rest-ing spores that have not been treated with acid is now required. To obtain it spores have been cut into thin slices with the aid of a sectioning technique recently developed for electron micros-copy (Newman et al., 1949; Hartmann and Latta, 1950). The study of these sections has clarified the normal disposition of the nuclear material in resting spores and the extent of its disarrangement when whole spores are subjected to the Feulgen process and other procedures in-volving acid hydrolysis. MATERIALS AND METHODS Spores of Bacillus cereus and Bacillus mega-terium have been examined. Details of the for-mer have been given by Robinow (1951); the latter culture was freshly isolated and some cyto-logical features of spores of this strain have al-ready been described (Robinow, 1953). B. cereus was grown in Povitzky bottles, on the agar medium of Howie and Cruickshank (1940), fortified with 1 per cent casamino acids. Spores were harvested after 9 days, washed repeatedly with distilled water, largely freed from vegetative forms by differential centrifu-gation, and dried to a powder in vacuo over sulfuric acid. The dry spores were kept in glas