“…At an early period in the history of the use of whale-liver oils as a source of vitamin A a commercial concentrate was studied (Edisbury et al 1935(Edisbury et al , 1937 It speedily emerged in these laboratories, and in those of Lever Brothers and Unilever Ltd. at Port Sunlight, that neither the colour test nor the ultraviolet absorption was anomalous in a constant fashion, and the basis for the empirical use of a conversion factor of 1200 instead of 1600 (widely used for fish-liver oils) disappeared. The correction procedure ofMorton& Stubbs (1946) was often stretched beyond the limits of its utility by the magnitude of the irrelevant absorption. It had also become clear that the factor of 1600 was itself a reflexion of the fact that, on the average, fish-liver oils exhibited some 11 % or so of 'irrelevant' absorption and that a factor of 1800 was appropriate to preparations in which vitamin A was the only significantly absorbing entity (Morton & Stubbs, 1947 light petroleum).…”