Lipoid Metabolism in the Developing Chick and Its Relation to Calcification

The liver of the embryo chick during the first two weeks of development contains an abundance of isotropic fatty globules which represent a mixture of lipoids in which phosphorized fats predominate. During the third week of incubation the fatty globules in the liver change their physical and chemical characters. They become anisotropic and exhibit the reactions and properties of esters of cholesterol. The phosphorized fats gradually disappear from the liver during the third week. The phosphoric acid utilized by the embryo chick in calcification is derived from phosphorized fats. It is suggested that the phosphorized fats are split in the liver, the glycerophosphoric acid portion being liberated for calcification, while the free fatty acids are esterfied by cholesterol. A review of chemical analyses of aortic atherosclerosis and calcification made by others, and a comparison of the conditions in atherosclerosis with those of the developing chick liver, suggest that pathological calcification results from a splitting in situ of phosphorized fats with subsequent formation of calcium salts, as suggested by Baldauf.