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The extensive studies reported on the biological effects of cholesterol administration are chiefly concerned with changes brought about in the lipid composition of tissues. In the blood only the cholesterol fractions have been systematically examined after cholesterol feeding (cf. Anitschkow & Cowdry, 1933); only a few workers have examined the other blood lipids. Page & Bernhardt (1935), who fed rabbits with cholesterol dissolved in olive oil, reported that besides free and esterified cholesterol the phospholipids were increased in the plasma. Weinhouse & Hirsch (1940) found that phospholipids and neutral fats, as well as the cholesterol fractions, were increased in the serum of rabbits after cholesterol feeding. Vermeulen, Dragstedt, Clark, Julian & Allen (1942) also found that there was a great rise in the 'non-cholesterol fraction' of the serum lipids ofrabbits fed cholesterol dissolved in sunflower-seed oil. The studies quoted were concerned chiefly with the experimental production of atheroma; the plasma-lipid values were estimated only after a very long period ofcholesterol administration and no attempts were made to elucidate the mode of action of cholesterol. Most of the changes in tissueand blood-lipids reported as having been brought about by exogenous cholesterol cannot strictly be attributed to cholesterol alone (except those found by Weinhouse & Hirsch), but to cholesterol plus a high fat diet. It was generally held until recently that cholesterol is not appreciably absorbed from the alimentary tract unless fats are administered with it (cf. Bloor, 1943, pp. 106-8). This is apparently true only for crystalline cholesterol, for Domosi & Egyed (1939) have shown that cholesterol is readily absorbed from the alimentary tract of rabbits if it is administered in the form of an amorphous suspension in water. The total blood-cholesterol level of their rabbits, fed 1 g. of cholesterol daily, rose in 4-5 days from the normal ofabQut 80 to 300-400 mg./100 ml., and in 3-4 weeks the rabbits developed atheroma in the aorta and pulmonary arteries and the total blood-cholesterol levels reached 1300-1800 mg./ 100 ml. Domosi & Egyed made no observations on non-cholesterol lipid fractions in the blood and their earliest observations were made after 4 days of cholesterol administration. The experiments to be reported here were originally designed to study the effect of cholesterol on the kidney lipids. It might be mentioned that while cholesterol readily induces fatty livers'cholesterol-fatty liver' (Best & Ridout, 1933; Chanutin & Ludewig, 1933; Okey, 1933; Best, Channon & Ridout, 1934; Channon & Wilkinson, 1934)-in fhe kidney only negligibly small amounts of cholesterol or neutral fat are deposited in the tubular epithelium during cholesterol feeding. In these rabbits' kidneys cholesterol accumulated only in the interstitial cells and capillary endothelium. The plasma-lipids during the experiments were also investigated and results were obtained which are thought to cast some new light on the rather obscure role of cholesterol in fat metabolism. The changes observed in plasma-lipids in the present experiments can be attributed entirely to the action of cholesterol as no fats, save the small amounts contained in the usual vegetable diet, were administered to the rabbits.

The effect of feeding cholesterol without fat on the plasma-lipids of the rabbit. The role of cholesterol in fat metabolism