Abstract
The lack of agreement as to what constitutes subclinical vitamin A deficiency and the uncertainty existing as to the order of the occurrence of the supposed early signs in relation to one another prompted the undertaking of this study. The various suggested symptoms of early avitaminosis A include: defective dark adaptation, macroscopic and microscopic changes in the skin and conjunctivas, changes in the total and differential white blood counts and decreased vitamin A content of the blood. Each of these factors has been investigated individually: there have been studies in which only two or three of the aforementioned signs have been followed in any one subject, the most usual method being to observe dark adaptation and one other sign. It was believed, therefore, that careful observations for all of the suggested subclinical signs of progressive vitamin A deficiency in the same subjects on a vitamin A—low diet would at least
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