The study of diseases in man due to the lack of various essential dietary constituents is still far from complete. The results of feeding experiments with animals have helped to define the rôle of an ever increasing number of vitamins and have served to focus attention on the most conspicuous manifestations of individual deficiency diseases in man. But, as Keefer and Yang1 have recently emphasized, the exact methods of the laboratory are not obtainable with observations on human disease. The diet of the experimental animal is chosen with meticulous care; that of the human being is dictated by geographic location, class or racial custom, individual appetite and the exigencies of economy. A diet so limited as to be deficient in one essential is liable to be defective in several. It is true that the resulting disease may be dominated by symptoms pointing to the absence of one definite constituent,
WEECH AA. ASSOCIATION OF KERATOMALACIA WITH OTHER DEFICIENCY DISEASES. Am J Dis Child. 1930;39(6):1153–1166. doi:10.1001/archpedi.1930.01930180003001
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