Cholesterol possesses many points in common with the fats and lipoids and is, therefore, usually grouped with these substances. Its presence in the blood seems to go hand in hand with that of the fats, and the quantitative relationship it bears to them is fairly constant. By virtue of this and the fact that it can readily be determined quantitatively, estimates of cholesterol are often used as a measure or index of the total fat content of the blood. The origin of the cholesterol of the blood is not definitely known; some of it is undoubtedly exogenous, and some endogenous. It is subject to marked fluctuations under a variety of conditions. In some it appears to be independent of external causes and definitely associated with metabolic disturbances, as in diabetes, nephritis,1 etc. There also can be no doubt of the relation of the blood cholesterol to the glands of internal