THE EGG. 637 



monamino-acids, especially leucine, but not glycocoll or glutamic acid, is to 

 all appearances not a unit body. The eggs of the river-crab and the lobster 

 contain the same pigment as the shell of the animal. This pigment, called 

 cyanocrystallin, becomes red on boiling in water. 



C. MORNER l has isolated a substance which he calls percaglobulin, from the 

 unripe eggs of the river-perch. It is a globulin and has a strong astringent taste. 

 Especially striking is its property of precipitating certain glycoproteins, such as 

 ovomucoid and ovarial mucoids, and polysaccharides, such as glycogen, gum, 

 tragacanth and starch-paste, and of being precipitated by them. Percaglobulin 

 could not be obtained by MORNER from the eggs of the sea-bass. 



In fossil eggs (of APETNODYTES, PELECANUS, and HALL.EUS) in old guano deposits, 

 a yellowish-white, silky, laminated compound has been found which is called 

 guanovulit, (NH 4 )2S04-h2K 2 S04+3KHS0 4 +4H 2 0, and which is easily soluble in 

 water, but is insoluble in alcohol and ether. 



Those eggs which develop outside of the mother-organism must con- 

 tain all the elements necessary for the young animals. One finds, there- 

 fore, in the yolk and white of the egg an abundant quantity of protein 

 bodies of different kinds, and especially phosphorized proteins in the 

 yolk. Further, we also find abundance of phosphatides in the yolk, 

 which seem to occur habitually in all developing cells. KATO and BLEIB- 

 TREU 2 found glycogen in the eggs of the frog which during the spawning 

 season increased at the cost of the liver glycogen. Besides this the egg 

 is very rich in fat, which doubtless is important as a source of supply 

 for nourishment and in maintaining respiration for the embryo. The 

 cholesterin or at least the lutein can hardly have a direct influence on 

 the development of the embryo. The egg also seems to contain the 

 mineral bodies necessary for the development of the young animal. 

 The lack of phosphoric acid is compensated by an abundant amount of 

 phosphorized organic substance, and the nucleoalbumin containing 

 iron, from which the hsematogen (see page 629) is formed, is doubtless, as 

 BUNGE claims, of great importance in the formation of the haemoglobin 

 containing iron. The silicic acid, necessary for the development of the 

 feathers, is also found in the egg. 



During the period of incubation the egg loses weight, due chiefly to 

 loss of water. The quantity of solids, especially the fat and the proteins, 

 diminishes, and the egg gives off carbon dioxide, but TANGL disproves 

 the older claim of LIEBERMANN 3 that nitrogen or a nitrogenous substance 

 is given off. On the contrary a corresponding absorption of oxygen 

 takes place, and it is found that during incubation a respiratory exchange 

 of gases occurs. 



As BOHR and HASSELBALCH have shown by exact investigations, the 

 elimination of carbon dioxide is very small in the first days of incuba- 



1 Zeitschr. f. physiol. Chem., 40 and 58. 



*Kato, Pfluger's Arch. 132; Bleibtreu, ibid., 132 (1910). 



* Tangl and v. Mituch, Pfluger's Arch., 121; Liebermann, ibid., 43. 



