Abstract
1. The bacteriophage for Bacterium malvacearum E. F. S. was obtained from the aqueous suspension of the crushed, diseased cotton leaves which had been kept at 10°C for three weeks.
2. The potency of the lytic principle was determined by the following two methods: (1) Dilution method; (2) plaque formation on the potato dextrose agar. The former reveals that the filtrate of three passages has given the titre of 10-7. According to the latter it is found that a loopful of the 1/100 diluted filtrate (the 7th passage) has produced 4 plaques and the same amount of the 1/10 filtrate has given 109. Three drops of the same filtrate seem to be the limit for accurate counting of plaques, as they have given 1950 plaques.
3. The greatest lytic activity may be found near 28°C or between 25°C and 28°C and in all probability the maximum lytic activity approximately parallels the maximum growth of the homologous bacteria. It seems likely that 37°C is near the maximum temperature, and the minimum may come below 10°C.
4. Any of the four strains isolated from the phagic cultures has been proved to be highly resistant to the lytic action. In no case was a strain susceptible to the lytic action recovered. The pathogenicity of these resistant strains, however, has not been appreciably differed from the original, so far as the results of the inoculation on detached cotton bolls are concerned.
5. The size of the plaques produced on the potato dextrose agar varies according to the difference of agar concentration, and enlarges to a certain extent with the increase of the incubation period. In general, the more diluted the agar is, the larger the plaques are.
