Seven vitamins have to date proved essential for the survival and multiplication of a mouse fibroblast (strain L) and a human carcinoma cell (strain HeLa) in tissue culture: choline, folic acid, nicotinamide, pantothenic acid, pyridoxal, riboflavin, and thiamin. It was necessary to cultivate the cells for 5 to 15 days in a medium lacking the specific vitamin before the deficiency became apparent in the cessation of multiplication and the development of specific cytopathogenic effects. In their early stages these changes could be reversed by the addition of the missing vitamin, an in vitro, "cure" of a vitamin deficiency. The maximally effective concentrations were in the range 107 to 108 gm. per ml.

The probability that additional vitamins not demonstrably essential under the conditions of the present experiments are nevertheless required for survival and growth is discussed in the text.

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