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628 ORGANS OF GENERATION.
The Ovum.
The small ova of man and mammals eannot, for evident reasons, be
the subject of a searching chemical investigation. Up to the present
time the eggs of birds, amphibians, and fishes have been investigated,
but above all the hen’s egg. We will here occupy ourselves with the con-
stituents of this last.
The Yolk of the Hen’s Egg. In the so-called white yolk, which
forms the germ with a process reaching to the center of the yolk (latebra),
and forming a layer between the yolk and yolk-membrane, there occurs
protein, nuclein, lecithin, and potassium (Liebermann l
). The occur-
rence of glycogen is doubtful. The yolk-membrane consists of an albu-
minoid similar in certain respects to keratin (Liebermann).
The principal part of the yolk—the nutritive yolk or yellow—is a
viscous, non-transparent, pale-yellow or orange-yellow alkaline emulsion
of a mild taste. The yolk contains vitellin, lecithin, cholesterin, fat, color-
ing-matters, traces of neuridine (Brieger 2
), purine bases (Mesernitzki 3
),
glucose in very small quantities, and mineral bodies. The occurrence of
cerebrin and of granules similar to starch (Dareste 4
) has not been posi-
tively proved.
Several enzymes have been found in the yolk, especially a diastatic
enzyme (Muller and Masuyama), a glycolytic enzyme (Stepanek)
which in the absence of air brings about an alcoholic fermentation of
sugar and in the presence of air forms carbon dioxide and lactic acid,
and finally a proteolytic, a lipolytic, and a chromolytic (?) enzyme
(Wohlgemuth 5
).
Ovovitellin. This body, which is often considered as a globulin
is in reality a nucleoalbumin. The question as to what relation other
protein substances, which are related to ovovitellin, like the aleuron
grains of certain seeds, and the yolk spherules of the eggs of certain fishes
and amphibians, bear to this substance is one which requires further
investigation.
The ovovitellin which has been prepared from the yolk of eggs is not a
pure protein body, but always contains lecithin. Hoppe-Seyler found
25 per cent lecithin in vitellin. The lecithin may be removed by boiling
alcohol, but the vitellin is changed thereby, and it is therefore probable
1
Pfluger’s Arch., 43.
1
Ueber Ptomaine, Berlin, 1885.
a
Mesernitzki, Bioehem. Centralbl., 1, 739.
* Compt. Rend., 72.
6
Muller and Masuyama, Zeitschr. f. Biologie, 39; Stepanek, Centralbl. f. Physiol.,
18, 188; Wohlgemuth in Salkowski’s Festschrift and Zeitschr. f. physiol. Chem., 44.
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