In 1923 Levaditi and Nicolau1 described the manner in which tumor growth is inhibited. They believed that the virus grows in the tumor and destroys it. The virus usually prefers tumor tissue to the organ it invades. Anything which interferes with viral multiplication, such as an immune host, destroys the carcinolytic activity. The unique feature of this relationship is that each virus has its own tumor spectrum, destroying some, growing in but not destroying others, and not growing in still others. We are unable to determine if a virus will destroy a tumor until it is subjected to direct test.
Koprowski et al.2 (1957) have shown that by inducing tolerance in an animal it is possible to grow tumors in other strains of mice, or even in other species. These derived tumors were often susceptible to destruction by virus, although the original tumor failed to support virus growth.