In 1960 a virus was proven to cause a cancer in chickens. It was the first time a virus was found definitely to cause a cancer and the first time a cancer was shown to be contagious. The proof of this finding was affirmed by using Robert Koch's postulates, a set of sensible procedures which eliminate the possibility that there is more than one cause for an effect. First the agent must be isolated from affected individuals and then grown in pure cultures. Next normal individuals exposed to the cultured agent must contract the disease the agent is assumed to cause. Finally the same agent must be isolated from the exposed individuals who contracted the illness.

Researching Sarcoma Cause.

Dr. B. R. Burmester of the U.S. Department of Agriculture Regional Poultry Laboratory in East Lansing, Michigan, applied Koch's postulates to the Rous sarcoma virus...