Free Vaccinated by Paul A. Offit Page A

concerned. His fears stemmed from an event that had occurred fifty years earlier.
    In 1909 a farmer walked into the Rockefeller Institute in New York City carrying a dead chicken under his arm. Hands thickened by hard work, wearing thick bib overalls and heavy boots, the farmer watched as scientists, technicians, and graduate students milled through the lobby of one of the country’s premier research institutes. Finally he got up the courage to ask where he could find Peyton Rous’s laboratory. The farmer was certain that Rous, an expert in animal diseases, would know what had happened to his chicken.
    A Baltimore-bred, Johns Hopkins–trained pathologist, Peyton Rous was thirty years old when he took the chicken from the farmer, laid it onto his laboratory bench, and dissected it. Just under the right breast was a large cancerous tumor. Rous found that the cancer had also spread to the liver, lungs, and heart. He asked the farmer whether any other chickens in his flock had a similar problem. “No,” the farmer said, “only this one.” Apparently, the cancer wasn’t contagious.
    Rous wanted to find what had caused the chicken’s cancer. So he removed the tumor and carefully ground it up with sterile sand, completely destroying all the malignant tumor cells. Then he suspended the disrupted tumor cells in salt water and passed them through unglazed porcelain, which acted as a filter to trap bacteria. Rous found that when he injected the fluid that had passed through the filter into other chickens, tumors developed in those chickens as well. Within a few weeks, cancer had killed them all. “The [chickens] became emaciated, cold, and drowsy, and shortly died,” he said. Because the tumors were caused by something passing through the filters, Rous knew that it couldn’t be bacteria. And he knew that it couldn’t be the cancer cells, because they had been destroyed by the sand and were too big to pass through the filters. It was something else. Rous reasoned that the agent that had passed through the filters was a virus.
    On January 11, 1911, Peyton Rous, in a paper titled “Transmission of a Malignant Growth by Means of a Cell-Free Filtrate,” was the first person to prove that viruses could cause cancer. Immediately other investigators tried to duplicate Rous’s findings in mice and rats, but without success. Reasoning that cancer-causing viruses were at most a phenomenon unique to chickens, Rous gave up his investigations in 1915, and for the next four decades researchers relegated tumor viruses to the cabinet of freaks.
    Although many cancer researchers working in the 1910s through the 1940s ignored Rous’s findings, evidence continued to mount in favor of cancer-causing viruses. In the early 1930s Richard Shope, a veterinarian from Iowa, found that viruses caused giant warts on wild rabbits in the southwestern United States. (Although many consider them to be mythical creatures, jackalopes—jackrabbits with antelope horns—might be rabbits infected with Shope’s wart-causing virus.) A few years later, researchers found a virus that caused tumors in the mammary glands of mice. But it wasn’t until the 1950s, when Ludwik Gross, a Polish refugee, found a virus that caused leukemia in mice, that cancer-causing viruses came out of the cabinet and into the mainstream of virus research. Ten years later William Jarrett, working at the University of Glasgow in Scotland, found another virus that spread easily from one cat to another, causing leukemia. Not only did viruses cause cancer, but some cancer-causing viruses were also contagious.
    In 1966, more than fifty years after he had examined the farmer’s dead chicken, Peyton Rous won the Nobel Prize in medicine for “the discovery of tumor-inducing viruses.” Rous received the prize, which cannot be awarded posthumously, when he was eighty-six years old.
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