To recognize clinical and subclinical vitamin A deficiency the blood level of vitamin A,1 visual tests for night blindness,2 biomicroscopic changes in the cornea3 and other means have been used. The results obtained and the conclusions drawn have varied. Some authors have concluded that vitamin A deficiency is common4; others have considered it to be rare.5
The liver is the main storage place for vitamin A. It contains about 95 per cent of the total amount of the vitamin in the body.6 Therefore, it can serve as an index of the vitamin A status. Hence, it would seem that those tests for deficiency of the vitamin would be significant which parallel low or absent stores in the liver.
The present study deals with the significance of the vitamin A level of the blood. The vitamin A concentration of human blood plasma was compared with the vitamin A content