Clarity of high lipid sera is closely correlated with elevated proportions of serum phospholipids, and lipemia (milkiness) with low proportions of phospholipids. Clear high lipid sera occur uniquely in obstructive jaundice, both intra- and extrahepatic in origin.
Destruction of the polar nature of serum "lecithin" by enzymatic hydrolysis, using Cl. welchii lecithinase, results in a degree of lipemia which is linearly proportional to total lipid content in clear or lipemic high lipid or normal lipid sera.
Even in grossly lipemic sera, a significant proportion of the serum lipids is masked in particles of invisible size. Enzymatic removal of the stabilizing properties of serum "lecithin" unmasks this hitherto invisible fraction.
The concentration of serum phospholipids available for complex formation with serum proteins appears to be an important factor in determining particle size of serum lipids and hence of their occurrence in serum as masked or as visible particles.
The implications of these findings for studies of the genesis of atheromatosis are discussed.