1) The growth of bacterial cells (Bacillus subtilis var. amyloliquefaciens Fukumoto-K 49) was investigated under various pH values in 5 % soybean extract medium by estimating turbidity of culture solution. The optimum pH is 6.7-7.0 and this bacterium can not multiply at pH above 8 or pH below 5. 2) The plaque formed by K49-phage is clear and circular. Its diameter is 1-2 mm and it has a halo. The influence of temperature on the bacteriophage was examined by plating technique. It was found that the phage is stable for 40 minutes under 60'C, and that above this temperature the activity of phage decreases gradually with the increase of the temperature. The effect of pH-value on the phage was also studied by the same technique. In general, the phage is comparatively stable at the neutral solution and the activity of phage decreases at higher or lower pH. 3) The growth of K49-ph a g e was followed by One Step Growth Curves. Under the optimum condition (pH 7.0, at 37'C) in soybean extract medium this phage multiplies with the average burst size of about 70-95 and the latent period is about 40 minutes. 4) The burst size varies with the pH values ranging from 5.4-8.9, without changing of the latent period. When the host-phage complex was incubated at pH 7 and 37℃ for the initial 38 minutes after infection and then placed at pH 5.4 or 8.6, the phage could not multiply as in the standard medium. 5) This phage gives the greatest titer at 37℃. Although between 37℃ and 48'C, the average burst size is greatly affected but the latent period is not prolonged, the temperature between 37℃ and 22'C affects both the latent period and the burst size. 6) The latent period is also influenced by the age of host. The cells of logarithmic growth phase generally have a minimum latent period and those of stationary phase have a longer period. 7) It was revealed that the growth of the phage seems to keep pace with that of its host cell and is influenced by the biological and physical conditions.
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