296 , PHYSIOLOGICAL CHEMISTRY. 



magnesia, 4.4-5.5 iron oxide, 238.4-285.6 chlorine, 31.6-48.3 phos- 

 phoric acid (P 2 5 ), 13.2-26.3 sulphuric acid, 2.8-20.4 silicic acid 

 and 96.7-116 grms. carbon dioxide. Traces of fluorine have also 

 been found (NICKLES). The ash of the white of the egg contains, 

 as compared with the yolk, a greater amount of chlorine and alka- 

 lies, and a smaller amount of lime, phosphoric acid, and iron. 



The Shell-membrane and the Egg-shell. The shell-membrane 

 consists, as above stated (page 35), of a keratin substance. The 

 shell contains very little organic substance, 36-65 p. m. The 

 chief mass, more than 900 p. m., consists of calcium carbonate; 

 besides this there are very small amounts of magnesium carbon- 

 ate and earthy phosphates. 



The different coloring of birds' eggs depends, as WICKE, SORBY, LIEBER- 

 MANN and KRUKENBERG have shown, upon several coloring matters. Among 

 these we find a red or reddish-brown pigment called "oorodein" by SORBY, 

 which is perhaps identical with haematoporphyrin (SORBY, KRUKENBERG). 

 The green or blue coloring matter, SORBY'S oocyan, seems, according to 

 LIEBERMANN, and KRUKENBERG, to be partly biliverdin and partly a blue 

 derivative of the bile-pigments. 



The eggs of birds have a space at their blunt end filled with 

 gas ; this gas contains on an average 23.3 vols. per cent oxygen 

 (BISCHOFF). 



The weight of a hen's egg varies between 40-60 grammes and 

 may weigh sometimes 70 grms. The shell and shell-membrane to- 

 gether when carefully cleaned, but still in the moist state, weigh 

 5-8 grms. The yolk weighs 12-18 and the white 23-34, or about 

 double. 



The white of the egg of cartilaginous and bone fishes contains only traces 

 of true albumin, and the cover of the frog's egg consists, according to GTACOSA, 

 of mucin. The crystalline formations (yolk-spherules or dotterpldttchen) which 

 have been observed in the egg of the tortoise, frog, ray, shark, and other 

 fishes, and which are described by VALENCIENNES and FREMY under the 

 names, emydin, ichthin, icfithidin, and ichthulin, contain lecithin, nuclein, and 

 albumin. They probably correspond to the yellow yolk-globule in the nutri- 

 tive yolk of the hen's egg. The egg of the river crab and the lobster contain 

 the same pigment as the shell of the animal. This pigment, called cyano- 

 erystallin, becomes red on boiling in water. 



In fossil eggs (of APTENODYTES, PELECANUS, and HALI^EUS) in old guano 

 deposits a yellowish-white, silky, lamiated combination, has been found 

 which is called guanoyulit, (NH 4 ) 2 SO 4 -f 2K 2 SO 4 + 3KHSO 4 + 4H a O, and 

 which is easily soluble in water but is insoluble in alcohol and ether. 



Those eggs which develop outside of the mother-organism must 

 contain all the elements necessary for the young animals. One 



