In previous communications1 we have reported on the vitamin A requirements of infants and of children. The criteria which we used for estimating the vitamin A status of the subjects were (1) growth, (2) susceptibility to infections and (3) visual threshold in the dark (dark adaptation). The results of the studies indicated that, as judged by the aforementioned criteria, the requirement for vitamin A is low and that the average diet of infants and children contains several times the minimum requirement. It is for this reason that patients with frank vitamin A deficiency are so uncommonly observed in the clinic.
The possibility exists, however, that states of subclinical vitamin A deficiency are much more prevalent. In view of the fact that the level of vitamin C in the blood is now regarded as an indicator of the size of the stores of vitamin C in the body and is