578 



VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



and spleen, whereas this phospholipid, together with free cholesterol, de- 

 creased in both skeletal and cardiac muscle. All essential lipid compo- 

 nents except lecithin and cholesterol esters were found to increase in the 

 brain during growth. 



Fundamental differences distinguish the lipid metabolism of birds from 

 that of mammals. Entenman, Lorenz, and Chaikoff 262 reported that, in 

 contradistinction to the rat, the blood and liver lipids of chickens are ex- 

 ceedingly high at the time of hatching. The total liver lipids of the newly 

 hatched chicks averaged 13 to 14.7%, based upon wet weight, while values 

 as high as 23% were reported immediately after hatching. The high lipid 



Fig. 3. Liver fatty acids present as triglycerides, cholesterol esters, and phos- 

 pholipid: (•) cholesterol ester fatty acids in per cent; (A) phospholipid fatty 

 acids; (U) neutral fat fatty acids. Day H is day of hatching. 262 



content was maintained for only a short period after hatching; in most 

 cases a decline had already begun by the fourth day, and in all cases the 

 decrease was quite definite by the sixth day. The values for liver lipids in 

 the eight-day chick were 5.0 to 5.6%, while those on the twenty-second and 

 thirty-sixth day after hatching were between 1.6 and 3.2%. The changes 

 in the composition of the livers are indicated in Figures 2 and 3. 



In examining the composition of the lipids of the livers of the newly 

 hatched chicks, one is impressed by the enormous concentration of choles- 

 terol. During the first three days after hatching, values of 5.9 to 9.7% of 

 total cholesterol were recorded. 262 At this time, cholesterol comprised as 

 much as 48% of the total liver lipids. After three days, the decrease in 

 cholesterol content was rapid, with values of 1.0% recorded for the nine- 

 day-old and 0.5% for the eleven-day-old chick. Cholesterol levels in the 



