hypocholesterinemia than with a hypercholesterinemia. The fatty streaks of the intima of the aorta to which we are referring are lesions quite aside from true endarteritis as well as atheroma. In naked eye appearance the lesion is of a fatty nature and suggests atheroma, but it differs from this well-known lesion in the fact that the fatty materials, cholesterin-esters, are contained within cells which are of uniform type and have no reaction in their immediate vicinity. True atheroma may occur in definite levels of the intima, most commonly in the deepest portion, and is characterized by the fact that we are dealing with a variety of fatty materials, neutral fat, fatty acids, soap, cholesterin-ester and free cholesterin which lie between the tissue cells forming a detritus following a process of true degeneration. It is possible that some of the superficial fatty streaks do give rise to a small atheromatous area by death of the cells which primarily contain the fatty substances. Most commonly, however, the fatty streaks do not progress directly to atheroma but may entirely disappear, as we have seen it occur in our experimental animals. At other times these fatty streaks are followed by a slight thickening of the surface of the intima so that the resemblance to early endarteritis is obtained. We do not believe that these fatty streaks in themselves lead to the chronic nodular thickening of the aorta, but that other factors giving rise to a low grade inflammatory reaction must be present.