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W. K. Butterfield, C. F. Helmboldt, R. E. Luginbuhl, Studies on Avian Encephalomyelitis. IV. Early Incidence and Longevity of Histopathologic Lesions in Chickens, Avian Diseases, Vol. 13, No. 1 (Feb., 1969), pp. 53-57
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Butterfield et al. (1969) studied this question.
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