BIOCHEMISTRY OF THE SEXUAL ORGANS 283 



amount of iron in organic combination, and it is this substance 

 which is responsible for the presence of iron in the yolk of the egg. 

 According to Bunge, 1 this substance plays an important part in the 

 formation of haemoglobin in the chick. It is the precursor of 

 haemoglobin, and has, therefore, been called by him haematogen. 

 It contains 519 per cent. P and 029 per cent. Fe. Plimmer 2 lias 

 isolated from egg-yolk another protein, Jivetin, soluble in water and 

 containing O'l per cent, phosphorus. 



Two different fats have been isolated from the yolk the one 

 solid, rich in palmitic acid; the other fluid, containing equal parts 

 of palmitic and oleic acids. A small amount of stearic acid is also 

 present in both fats. The composition of the fatty substances is 

 influenced by the food. According to Henriques and Hansen 3 the 

 fat of the food passes into the yolk in the same kind of way as it 

 passes into the fat deposits of the adult organism. The observations 

 of M'Collum and his collaborators 4 have given the extraordinary result 

 that the lecithins of the egg-yolk do not possess a specific composi- 

 tion, but that they are variable in respect of the nature of the fatty 

 acid radicals which they contain, and that these can be made to vary 

 by varying the food. 



The food has also an influence upon the colour of the yolk, which 

 is due to luteins. Feeding with grains produces a light yellow yolk, 

 a dark yellow yolk results if grass and herbs are given, while feeding 

 with worms leads to the production of an even darker reddish yolk. 

 What the changes are in the colouring matter of the yolk has not 

 yet been ascertained. 5 



During the development of the chick a considerable portion of 

 the fat disappears. In other words, a* certain amount of chemical 

 energy, which in the fresh egg is present in the form of fat, 

 disappears. Liebermann 6 has shown, for instance, that of 5'4 gm. 

 of fat present in a fresh egg only 2*7 gm. can be recovered 

 when the chick is hatched. The fate of the chemical energy which 

 has thus disappeared has been accounted for completely by the 

 observations of Bohr and Hasselbalch, 7 which are the most exact 



1 Bunge, " Uber die Assimilation des Eisens," Zeitsch. f. pftysiol. Chem., 1884, 

 vol. ix. 



2 Aders Plimmer, "The Proteins of Egg- Yolk," Join: ('/,<>. ,S'oc., 1908. 



3 Henriques and Hansen, "Uber den Ubergang des Nahrungsfettes in das 

 Hiihnerei," Skandin. Arch. f. Physiol., vol. xiv., 1903. 



4 M'Collum, Halpin, and Drescher, "Synthesis of Lecithin in the Hen," 

 Jour. Biol. C/iem., vol. xiii., 1912. 



5 For the morphological distribution of the constituents of the yolk, see 

 Waldeyer, " Die Geschlechtszellen," in Hertwig's Handbuch der Entwicklungs- 

 lehre der Wirbeltiere, vol. i., Jena, 1903. 



6 Liebermann, " Embryochemische Untersuchungen," Pflttgei** Arch., vol. 

 xliii., 1888. 



7 Bohr and Hasselbalch, " Uber die Warmeproduktion und den Stoffwerhsel 

 des Embryo," Skandin. Arch. f. Physiul., vol. xiv., 1903. 



