The particle size was of great influence as may be seen from the table. Sand was found most efficient when the grain size was between sieve numbers 40 and 60, while glass beads destroyed bacteria most rapidly when they passed sieve No. 60, but not 80. An increase in size resulted in a lower death rate, and a decrease had the same effect. Vegetative cells were more sensitive than spores, but the difference was not great. With the spores of Bacillus cohaeren8, when shaken with glas beads in distilled water, the death rate constant was K = 0.8. Escherichia coli under identical conditions had the constant 1.8. The same E. coli aken with the same glass beads in broth showed a death rate constant of only 0.8, the protection being probably due to the foaming. The spores of different species differ considerably in their sensitivity to mechanical destruction, as table I shows, and this difference is not correlated with the difference in heat resistance.

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4 on February 25, 2017 by guest Downloaded from STERILIZATION OF MICROORGANlSMS According to Campbell-Renton (1942b), bacteriophage is sensitive to shaking, but a great variation of sensitivity was observed with different phages. The shaking was carried out without addition of solid particles. With Salmonella schottmuelleri, the phage was inactivated to a much greater extent than the bacteria. It is possible to obtain apparently phage-free cultures of bacteria by shaking, provided that the culture is not too heavily infected with phage. 2. Death by pressure. It is not very probable, reasoning a priori, that pressure can affect bacteria suspended in a liquid.


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