Ludwik Gross

Summary1. Extracts prepared from livers, spleens, and lymphatic tumors of leukemic Ak mice, were centrifugated at 1400 × g (15 minutes), then 7000 × g (5 to 10 minutes), and finally passed through Selas porcelain niters. The filtered extracts were then inoculated into newborn (less than 16 hours old) C3H or C3H(f) suckling mice. 2. Of the 84 mice inoculated with fresh, filtered extracts, 9 died from leukemia, and 15 others developed bilateral epitheliomas possibly arising in the salivary glands. Of the 54 control litter-mates inoculated with heated (68°C for 30 minutes) extracts, only one developed a cervical tumor. 3. Extracts prepared from Ak leukemic cells may therefore contain 2 different agents, pathogenic for newborn C3H or C3H(f) mice: one, causing leukemia, and another salivary gland epitheliomas. These agents may differ in size. 4. It is assumed that the leukemic agent may interfere with the tumor agent preventing it from exerting its pathogenic properties on the cells of its usual Ak, carrier host, or that mice of the Ak line may be naturally resistant to the tumor agent. 5. Salivary gland tumors have not been observed in untreated mice of either the Ak, the C3H, or C3H(f) inbred lines.

Summary1. A strain of a filterable mouse leukemia agent has been developed from a spontaneous Ak leukemia through several successive cell-free inoculations of newborn C3H mice. 2. This agent induced acute, generalized leukemia within 2 1/2 to 3 1/2 months in 40 to 100% of the inoculated newborn C3H mice (Bittner substrain). 3. Newborn mice had to be inoculated; adult C3H mice were with few exceptions resistant to inoculation of the cell-free agent. 4. The leukemic agent could be preserved at −70°C from 46 days to 5 1/2 months, with no apparent loss of infectivity.

1. A filterable leukemic agent designated “virus X'recovered from a C3H female in which leukemia was induced by x-ray irradiation, was passed serially through 4 consecutive cell-free inoculations of suckling C3H mice. 2. Of 40 mice inoculated, 26 thus far developed leukemia (65%) at ages varying from 3 to 11 months. 3. Inactivated (56°C 1/2 hr) rabbit and guinea pig serum, prepared with agent X filtrates, only partially neutralized passage A leukemic agent; passage A immune rabbit serum had a distinct, though not complete neutralization effect on the passage A agent.