As found by earlier workers, , growing in broth at 37° was rendered incapable of gross multiplication either on nutrient agar or in nutrient broth by sudden cooling in many diluents at 4°. Killing is due to the joint action of a suitable diluent and of sudden chilling, since survival was complete either after sudden chilling in 0·3-sucrose or after gradual cooling in a potentially lethal diluent, such as Ringer's solution. Organisms in the stationary phase of growth were completely resistant. The susceptibility of growing organisms to sudden chilling changed rapidly during the exponential phase. Comparison with the survival after exposure to streptomycin, another bactericidal agent which has no effect on stationary phase cultures, showed that survival after chilling was not due to a fraction of the population being in the stationary phase. Sudden cooling of , strain B, infected with phage T2, had the same effect as ultrasonic disruption; namely, destruction of infective centres in the first half of the latent period followed, in the second half, by release of intracellular mature phage.


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