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It is not unusual for him to work a 16-hour day six days a week, though he tries to take most of Sunday off to be with his boys. Golf and tennis are only memories nowadays. Typical of Dr. Salk's concentration, and an example of his humor, is a story told by Mrs. Salk. She was talking to him about family matters and could tell by his faraway look that his thoughts were back in the lab. "Why, Jonas," she protested, "you're not listening to me at all." Grinned Dr. Salk: "My dear, I'm giving you my undevoted attention."
Medium No. 199. Salk's first chance to make a name for himself in polio work came in 1949. Baltimore's Dr. Bodian and Dr. Howard Howe had concluded that all known strains of polio virus belonged to three types, as far as immunity was concerned. If this were true, one strain of each would have to go into a vaccine, and no more. How to be sure? The National Foundation commissioned four university laboratories, including Dr. Salk's, to classify 100 strains. The task took three years, cost $1,370,000. Salk and his associates typed 74 strains. Along the way, Salk became a devotee of Enders' tissue culture technique (some "older and wiser" polio researchers missed the boat by neglecting this), and characteristically, he sought ways to improve it.
Dr. Salk set his growing staff to testing different parts of the monkey's anatomy to find the most useful virus-growing tissues. Like Enders, they found the kidney the best. But a question that Enders and his colleagues had not settled was the best broth in which to grow the tissue cells. Dr. Salk tested many, picked Medium No. 199, containing 62 carefully balanced ingredients, from common salt to penicillin, which Toronto's Dr. Raymond C. Parker had developed for culturing cancer cells.
It did not take Dr. Salk long to see that ready at hand were all the essentials needed, at least in theory, to make an effective polio vaccine: plenty of virus, grown safely in non-nervous tissue; convincing evidence that only three types of virus need be in the vaccine; means to kill or inactivate the virus and still leave it with the power to stimulate the human system to produce protective antibodies. The best way to kill the virus with formaldehyde solution was not known, but Dr. Salk tried dozens of different concentrations and temperatures. "When you try 30 variables," he says, "you're sure to hit the right one." Also unknown was the level, or titer, of antibodies a person must have to enjoy protection against polio. The Hurry-Up. Step by painstaking step, Dr. Salk made experimental vaccines and tested them in monkeys. In June 1952 he was satisfied that he had a vaccine safe enough to be given to human beings. Still, for utmost safety, he decided that the first subjects should be those who had already recovered from polio. Thus they should be immune to further disease, but he could measure a rise in their antibody level if the vac cine produced, as he expected, a booste effect. It did.