814 VII. LIPID DISTRIBUTION IN SPECIFIC TISSUES 



down in four days. A visible demonstration of the periodicity of fat de- 

 position in the egg yolk was given by Gage and Fish, 622 who used a unique 

 method. It was reported that, when stained fats were fed to laying hens 

 on certain days, the yolk fat was stained in layers corresponding to the fat 

 laid down during those particular periods. 



A number of workers h&ve recorded variations in the egg glycerides as 

 affected by diet. Thus, after feeding linseed oil to laying hens, Henriques 

 and Hansen 606 found that the iodine value of the glycerides was increased 

 from 70 (on the basal carbohydrate diet) to 97; when hempseed oil was 

 included in the diet, the iodine number of egg-yolk fat was 119 to 123. 

 Cruickshank 607 ' 608 likewise reported that the iodine number of egg-yolk fat, 

 as well as of depot fat, may be raised by feeding a fat having a high iodine 

 number. However, she found that the iodine number of egg yolk was 

 practically unchanged when more saturated fats, such as mutton fat or 

 palm oil, were fed. Reiser 609 observed that elaeostearic acid was deposited 

 in egg yolk after tung oil had been fed to hens. On the other hand, the 

 iodine values of both the glycerides and the phosphatides in egg yolk were 

 found to be lower in hens on a fat-free diet than when the birds had re- 

 ceived 3 to 4% of fat in the diet. 610 ' 611 



Reiser 612 noted that, when fat-free diets were fed to laying hens, there was 

 a marked decrease in the polyunsaturated acid content of the egg yolks. 

 The 6 double-bond acids were found to disappear from the glycerides after 

 the hens had received the fat-free regimen for four weeks. A oeriod of 

 eight weeks was required before the acids having 5 double bonds dis- 

 appeared from the egg yolks. The acids having 2, 3, or 4 double bonds 

 decreased in the yolks more slowly under these experimental conditions. 

 After fourteen weeks they had declined to 16 to 25% of the control level. 

 The variations in the phospholipid fatty acids resembled those in fatty 

 acids from the triglyceride fraction. When cottonseed oil was included in a 

 purified diet, the hexaenoic acids disappeared from the egg yolks, but the 

 other polyunsaturated acids were still present. It was concluded that the 

 hen cannot synthesize polyunsaturated acids from non-fat precursors, but 

 that it can form acids with 3, 4, and 5, but not with 6 double bonds, from 



606 V. Henriques and C. Hansen, Skand. Arch. Physiol, 14, 390-397 (1903). 



607 E. M. Cruickshank, Harper Adams Utility Poultry J., 17, No. 12, 626-632 (1932). 



608 E. M. Cruickshank, Biochem. J., 28, 965-977 (1934). 

 809 R. Reiser, Arch. Biochem. Biophys., 32, 113-120 (1951). 



610 E. V. McCollum, J. G. Halpin, and A. H. Drescher, J. Biol. Chem., IS, 219-224 

 (1912). 



611 E. F. Terroine and P. Belin, Bull. soc. chim. biol., 9, 12-48 (1927). 

 S1J R. Reiser, J. Nutrition, 40, 429-440 (1950). 



