“…It has been widely assumed that the site of the conversion of the active carotenoids into vitamin A is the liver itself, although the results of in vitro experiments designed to test this view are equivocal (see, e.g., Woolf & Moore, 1932). In the cow, carotenoids are present in the systemic blood plasma in amounts which reflect the dietary intake of carotenoids (Mitchell & Wise, 1944), and the plasma levels presumably represent a balance between absorption from the intestine and removal by the liver, the pigments being merely en route to the liver from the gut.…”