The work to be described in these communications followed earlier studies (Leitner & Moore, 1946;Leitner, Moore & Sharman, 1947), which were mainly concerned with the lowered blood vitamin A in certain diseases. For purposes of comparison it was desired to know the levels of vitamin A prevalent in normal subjects, and the advisability of obtaining more adequate information became apparent. It was known that the blood vitamin A varied widely in different normal individuals, and that men tended to have higher levels than women (Kimble, 1938-9), but knowledge was scanty on the influence of age or season of the year. Moreover, at the time of our earlier work, dietary restrictions, imposed during the Second World War, were still in force in this country. It was of interest, therefore, to study the effect on the blood vitamin A of the changes in the national food supplies which followed the gradual relaxation of controls.Specimens of blood were taken for a long period from numerous subjects, with the aim of collecting a mass of information large enough to counteract the disturbing effect on averages of the wide individual variations. Estimations of total carotenoids were made parallel with those of vitamin A. Vitamin E is known to be capable of intervening in the metabolism of vitamin A (Moore, 1939; Bacharach, 1940; Harris & Woodside, 194z), so our programme was extended to include estimations of vitamin E. The presentation of our results on vitamin E has, however, been assigned to a later communication (paper no. 2 of this series), and paper no. 3 will deal with observations on chronic hospital patients.
E X P E R I M E N T A LCollection of specimens. Blood was collected by venepuncture from volunteers who came to one of us (2. A. L.) for medical examination. Some were young men in good health, who were examined for purposes of life insurance or for their fitness to do arduous work abroad. Most of the subjects, however, had some complaint, and were examined with a view to diagnosis and treatment.