296 THE UNFERTILISED EGG [pt. iii 



prolonged extraction of the yolk with ether, a considerable proportion 

 of the phosphatides still remained behind, and could be extracted 

 with alcohol. It was thought for a long time that the phosphatides 

 and the vitellin were in chemical combination which was broken 

 by the alcohol, but since the paper of Fischer & Hooker in 1 9 1 6 the 

 general opinion has been that this combination is only physical. 

 Stern & Thierfelder isolated traces of the cerebrosides, phrenosin and 

 kerasin, from egg-yolk in 1907. 



The neutral fats and the lipoids of the yolk are variously affected 

 by the nature of the fats in the food of the fowl. Henriques & Hansen, 

 who were the first to investigate this subject, found that, if food con- 

 taining very unsaturated acids was fed to the laying hens, the neutral 

 fats in the eggs were affected, but not the fatty acid components of 

 the lecithin. Their figures are shown in Table 22. When the food 

 consisted of barley, pea or rice, the iodine number of the neutral 

 fats in the egg varied round about 77, but hemp or linseed sent it 

 up to about no, although no matter what the food was the iodine 

 number of the fatty acids in the phosphatide fraction remained con- 

 stant at 75 or so. Henriques & Hansen also found that the iodine 

 number of the fluid fatty acids of the neutral fat was normally 107-5, 

 and that the fluid and solid fatty acids of the phosphatide fraction 

 were 151-3 and 98-9 respectively. The former accounted for 64-3 per 

 cent, of the lecithin fatty acids. The experiments of Henriques & 

 Hansen have been repeated and confirmed by Belin and by Terroine 

 & Belin. The last-named workers, together with McCollum, Halpin 

 & Drescher, some years later reported that the lecithin fatty acids 

 would vary, as well as the neutral fatty acids, with the diet of the 

 hen. Their figures, which are given in Table 22, certainly show a 

 variation in the iodine numbers of both fractions. All these workers 

 recognised the presence of unsaturated acids in the yolk fat, and 

 Henriques and Hansen's figures came between the theoretical values 

 for oleic and linolic acids. 



Work was continued along these lines by McGlure & Carr. Using 

 pigeons, they found that the fat content of the eggs could only be 

 altered slightly by feeding rations high and low in fat. 



% fat in the eggs 

 Cocoanut fat ... ... ... 4-0 



Beef tallow ... ... ... ... 6-75 



Average of all fat diets ... ... 4-96 



Average of all non-fat diets ... 4-81 



