The authors are indebted to Mrs. Erminie B. Compton and Miss Carol L. Voss for assistance in compilation of data.* Subsequent to the submission of this manuscript for publication the term "coronavirus" was proposed to include the avian infectious bronchitis virus (IBV) group, the mouse heaptitis virus (MHV) group, and the human "avian IBVlike" virus group (Coronaviruses, Nature 220: 650, 1968).
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