To the Editor:—
Your editorial of some months ago (192:54, 1965) called attention to the production of tumors of the central nervous system in mice, by injection of the Rous agent. In the interim other viruses have been found to provoke somewhat similar results in small animals, especially mice, but now tumors in dogs (Nature209:884, 1966) have been induced by Rabotti and others working at the National Cancer Institute. Although nonmetastasizing, the gliomatous quality of many of these has been transparent, even when companion leptomeningeal sarcomas have been present. The animals were all quite young, none as much as 8 weeks old at death, with symptoms beginning in 15 days or a little more. Evidently, symptomatology was followed rapidly by general deterioration of the animals. The potentialities of viruses for provoking neoplastic changes continue as fascinating puzzles.