The author studied on the resistance of P. mori phage to some factors such as sunlight, ultraviolet light, temperature, dehydration, and pH. The following results were obtained.
(1) The grade of phage inactivation under sunshine depended on the strength of sunlight. The phages were completely inactivated by exposing to sunlight for 60min, in May, but not even for 180min in April.
(2) When the phage suspension was irradiated under a certain dosage of UV-light, the survival rate was higher corresponding to an increase of the initial phage concentration. The phages were inactivated almost completely by exposing to UV light at a distance of 40cm under 15W lamp (2537Å), for 40sec., if the initial phage concentration was less than 10³ per ml.
(3) The phages were able to form plaques at the range of temperatures from 2.5 to 25°C. The highest plaque forming efficiency with clear plaque was obtained at about 20°C, and the plaque formation was retarded at low temperatures. The activity of the phages in sterilized water was relatively stable when they were in high concentration and kept at low temperature.
(4) The phages dried on a cover glass maintained their activity for more than 50 days in a desiccator.
(5) The phage activity was stable at the range of pH 5 to 9 in bouillon.
From the foregoing results, it is evident that P. mori phage is more resistant to dehydration and dry heat compared with that of P. mori.