In an attempt to study the role played by the virus in leukemia induced by X-ray irradiation, the author described the successful serial passage of the cell-free filtrate from RF mice with leukemia by X-ray irradiaion.
Cell-free filtrate from RF mice with leukemia induced by exposure of the entire body to a single dose of X-ray was bioassayed by the inoculation to new-born RF mice within 16 hours of birth. Four of sixteen test mice developed leukemia in 357 days, 374 days, 616 days and 663 days respectively. Serial implantation of the cell-free filtrate was successful in 60 per cent, 6 of 10 test mice, on the second passage, and in 17 per cent, one of 6 test mice, on the third passage. No leukemia was induced by the inoculation of cell-free filtrate from normal RF mice.