LIPIDS PRESENT IN EGGS 815 



linoleic acid. 612 No changes in the moisture, fat, phospholipid or choles- 

 terol content of egg yolk were occasioned by the fat-free ration. 



In addition to triglyceride fats, fat-soluble components may likewise be 

 transferred to the yolk when they are present in the diet. Thus, Lorenz 

 and associates 613,614 reported that the Halphen test, which is characteristic 

 of malvaceous fats, was positive in both the depot fat and the egg-yolk fat 

 when malvaceous plants such as the little mallow (Malva parviflora), 

 the California tree-mallow (Lavatera assurgentiflora) , the marsh-mallow 

 (Althaea, spp.), or cottonseed meal were fed to the hens. However, it was 

 later shown that the fatty material responsible for the Halphen test could 

 not be transferred from the depot fat to that of the egg. 614 It is well 

 known that the proportion of carotenols, vitamin A, and vitamin D present 

 in the eggs is related to the quantity ingested by the hens. For a discus- 

 sion of this subject, the reader is referred to Volume III. 



b. The Effect of Incubation. Marked variations in lipid occur during 

 the incubation of hens' eggs. Needham 615 reported that the fat content of 

 the egg decreased 50% during incubation. A sudden inflection in the 

 curves of all types of lipids occurred at fourteen days, when an activation 

 of fat metabolism apparently took place. During the week before hatch- 

 ing, there was a considerable augmentation of the body fat of the embryo. 

 According to Cahn, 616 an increase in triglyceride fat occurs during incuba- 

 tion. This rise is greatest after the fourteenth day. After the tenth day 

 of incubation, an increase in unsaturation of fats obtains; this is apparently 

 due to a selection of lipids to be retained, since the early embryo is incapable 

 of desaturating the fatty acids. 617 During the later periods, from the thir- 

 teenth to the twentieth day, the iodine value increases. 



Practically no change in the phospholipids occurs during the incubation of 

 hens' eggs until the sixteenth day, after which they begin to diminish rapidly, 

 with a concomitant increase in inorganic phosphorus. 618,619 Kugler 620 

 reported that the initial lecithin : cephalin ratio of 3 : 1 is maintained, both in 

 the yolk, in which a decrease occurs, and in the embryo, in which the phos- 



613 F. W. Lorenz, H. J. Almquist, and G. W. Hendry, Science, 77, 606 (1933). 



614 H. J. Almquist, F. W. Lorenz, and B. R. Burmester, J. Biol. Chem., 106, 365-371 

 (1934). 



615 J. Needham, Chemical Embryology, Vol. II, Cambridge Univ. Press, 1931, pp. 1163 

 ff. 



618 T. Cahn, Inaugural Dissertation, Paris, 1928; cited by J. Needham, Chemical 

 Embryology, Vol. II, pp. 1167, 1169 ff. 



617 E. C. Eaves, /. Physiol, 40, 451-453 (1910). 



618 R. H. A. Plimmer and F. H. Scott, J. Physiol, 88, 247-253 (1909). 



619 Y. Masai and T. Fukutomi, J. Biochem. (Japan), 2, 271-277 (1923). 



620 O. E. Kugler, Am. J. Physiol, 115, 287-291 (1936). 



