SECTION II 

 FAT METABOLISM 



1 1 -I. Fat Metabolism of Avian Eggs 



One of the first definite pieces of information acquired about the 

 chemical changes during incubation was that the "fats" diminished 

 in quantity. As early as 1846 Prevost & Morin reported that the 

 total ether extract diminished from 10-72 per cent, of the egg- 

 contents at the beginning of development to 9-82 per cent, on the 

 7th day, 9-48 per cent, on the 14th day and 5-68 per cent, on the 

 2 1 St day. This was confirmed by Sacc in the following year, who 

 made these interesting reflections: "Life is an ardent fire which needs 

 nourishment incessantly; its activity is such that it will even devour 

 its own hearth if it can find no other combustible. That is the reason 

 why the same wisdom which we admire throughout nature has put 

 at the disposal of the life in the egg this so abundant oil the destruction 

 of which prevents that of the albumen. Without this oil of which the 

 yolk is full (for it is in the yolk that the first traces of the embryo 

 are formed) the albuminous matter would be burnt up by the oxygen 

 of the air so that the development of the chicken could not go on", 



Liebermann, in his important paper of 1 888, decided that the fatty 

 acids of the egg-contents were distributed thus : 40 per cent, oleic, 38 

 per cent, palmitic and 15 per cent, stearic. During incubation in 

 one experiment the amount of "ether-soluble fatty substances" 

 diminished from 5-401 gm. to 2-729 gm., and his general conclusion 

 was that 2-672 gm. of fat were lost by an egg during development. 

 This confirmed the older observations of Parke in 1 866 and of Pott 

 in 1879, but it is only since 1900 that data have been obtained of 

 sufficient accuracy to allow of comparisons with those concerning 

 protein and carbohydrate metabolism. Nevertheless Liebermann's 

 figures were sufficiently definite to illuminate the subsequent re- 

 spiratory researches of Bohr & Hasselbalch, and to lead to the con- 

 clusion that the expired carbon dioxide could be completely accounted 

 for by the missing fat. It was here, of course, that the inaccuracy of 

 the estimation methods for fat upset the calculations, and the quan- 

 titatively minor though very important participation of proteins and 

 carbohydrates was overlooked. 



