The age factor in adaptability of a sarcoma virus to other animal species

The age of the chicken in which the Rous sarcoma is grown has an influence on the variation and subsequent adaptation of the causative virus to ducks. Adaptation is relatively easy to accomplish when the tumor has been grown in adult chickens several months of age. It has never been accomplished when the tumor has been grown in chicks and only occasionally when it has been grown in old chickens.