¶Several laboratories are working on the problem of finding a Type I strain of virus that will produce immunity, but with less danger of accidentally causing paralysis than the Mahoney strain now used in the Salk vaccine, reported Surgeon General Leonard A. Scheele in the A.M A Jour-ml. Researchers at Philadelphia Children's Hospital meanwhile disclosed first details of their method for making a preparation that is virtually pure polio virus (TIME June 20). They use a zinc salt to precipitate the virus, then a centrifuge to separate it from unwanted kidney tissue and chemicals. They concentrate 15 gallons to a teaspoonful,...
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