1) Studies in cholesterol metabolism; 2) Studies on the oxidation of colloidal aqueous solutions of carotene
Further experimental work on animals lis obviously required before any definite conclusion can be reached as to the effect of diet on the total output of bile and cholesterol, but the evidence of the foregoing experiments on human beings indicates that there is no direct correlation between the intake of cholesterol and its level in the blood and bile. Strong support is given to these observations by a recent (193) publication by Heymann & Rack (39) who investigated exogeneous cholesterol metabolism in children. These workers were unable to demonstrate any regular response in the serum cholesterol after the administration of single doses of the pure substance dissolved in olive oil and other solvents (cholesterol tolerance curves) or its daily administration for periods of two to four weeks. Furthermore, prolonged administration of "lipoid- free" diets did not lead to low serum cholesterol in their subjects, and they call attention to the confirmation given to their results by observations on children suffering from coeliac disease, in which there is practically no absorption from the intestine, leading to a state of chronic inanition. In this disease the insufficient absorption of amino acids leads to a definite hypoproteinaemia while the same inability to absorb cholesterol does not invariably decrease the amount of cholesterol in the blood below normal.Heyman & Rack believe that "the human organism is impressively independent of either the administration or the withdrawal of exogeneous cholesterol ", a view which is held by the present writer. Certainly the observations recorded in this paper afford no support to the contention that foods rich in cholesterol should be prohibited in the diet of patients with cholecystitis and cholelithiasis. The exclusion of butter, fat, eggs and liver from the diet of patients with diseases of the biliary tract is based essentially on the fact that gallstones are formed from cholesterol and the hypothesis that a reduction in the intake of cholesterol accordingly reduces the liability to gallstone formation. Such a low -fat, low -cholesterol diet is unphysiological because fat is the natural stimulant to biliary contraction and drainage, and has the further disadvantage of being unpalatable, monotonous and low in fat-soluble vitamins.