1. IUPAC, The Vitamin A Potency of β-Carotene (Butterworth, London 1959).
2. FAO/WHO, FAO Nutr. Meet. Rep. Ser. No. 41/World Health Organ. Tech. Rep. Ser. No. 362 (FAO, Rome 1967).
3. Canada Department of Agriculture, Biological Values of Provitamins A for Man, Domestic Animals and Birds (Can. Dep. Agr. Publ. No. 1238) (Roger Duhamel, F.R.S.C., Ottawa 1966).
4. J. Nadai and G. Brubacher, in Fat-Soluble Vitamins (International Encyclopaedia of Food and Nutrition, Vol. 9), ed. by R.A. Morton (Pergamon Press, Oxford 1970), p. 449.
5. R. Ferrando, Cah. Nutr. Diet., in the press (1971).