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An attempt has been made to rule out possible causes of artefacts in establishing survival curves of Bacillus licheniformis spores heated (30–80 °C) in 4.4 mol/l hydrogen peroxide (pH 2.0). A tailing phenomenon apparent as that of a suspension of spores produced by routine subculture was obtained with those grown‐up from a single spore selected by micromanipulation. No spore fraction differing in size or density could be separated from the whole population. The tail was not due to decomposition of hydrogen peroxide, protective effect by other spores, release of protective factors, or temperature heterogeneity during treatment. Changing from an open vessel to a closed tube did not influence the tailing. The only apparent artefact was therefore the formation of clumps under the conditions of the treatment. Since the spore catalase was demonstrated to be highly resistant, it was concluded that a spore could be protected against hydrogen peroxide by the catalase of the other spores in the clump. Conditions resembling those arising in spore suspensions could occur under industrial conditions, for example in sterilizing surfaces contaminated with aggregates of Bacillus spores.
Cerf et al. (Wed,) studied this question.