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THE EGG. G37
monamino-acids, especially leucine, hut 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 pcrcnglobulin, 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, (NH4)2S04-r-2K2S04+3KHS04-f-4H20, 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 haematogen (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, Pfliiger’s Arch. 132; Bleibtreu, ibid., 132 (1010).
* Tangl and v. Mituch, Pfluger’s Arch., 121 ; Liebermann, ibid., 43.
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