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aDepartment of Bacteriology and Immunology, University of Minnesota, Minneapolis, Minnesota
2
Present address: Department of Medical Microbiology, University of Kansas Medical Center, Kansas City 3, Kansas.
3
Present address: Department of Bacteriology and Medicine, Medical School, University of North Carolina, Chapel Hill, North Carolina.
1
This investigation was supported by a research grant from the Division of Research Grants and Fellowships of the National Institutes of Health, U. S. Public Health Service.