ABSTRACT
The occurrence of relatively large stores of vitamin A in the liver oils of many fish has naturally aroused considerable interest in the ultimate origin of this source of the vitamin. From the results obtained by a number of workers, there is no doubt that many constituent organisms of the plankton exhibit the biological activity associated with vitamin A (Jameson et al. 1922; Hjort, 1922; Ahmad, 1930; Drummond & Gunther, 1930), but, whilst it is probable that the carotenoids produced (presumably photochemically) by certain phytoplanktonic organisms are converted into vitamin A itself in vivo in some of the organisms constituting the zooplankton, precise information as to the exact locale of this conversion is lacking. Thus, whilst shrimps (Hjort, 1922) and molluscs (Jameson et al. 1922) have been shown to exhibit the biological activity of vitamin A, some samples of zooplankton have been found to possess no activity of this nature at all (Drummond & Gunther, 1930, 1934).
