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2. Fowler E. P.Jr.: Medicine of the Ear. Thomas Nelson and Sons, page 155.
3. Rose M. S.: The Foundations of Nutrition. Macmillan Co., pp. 218, 219, 293, 300, 1938.
4. LIMITS OF THE ANTI-INFECTIVE VALUE OF PROVITAMIN A (CAROTENE)
5. Eddy W. H., Dalldorf G.: The Avitaminoses. Williams and Wilkins, pp. 258, 262, 263.