628 ORGANS OF GENERATION. 



The Ovum. 



The small ova of man and mammals cannot, 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 1 ). 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 (BniEGER 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 p ^ds, 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 Pfliiger's Arch., 43. 



2 Ueber Ptomaine, Berlin, 1885. 



8 Mesernitzki, Biochem. Centralbl., 1, 739. 

 4 Compt. Rend., 72. 



6 Miiller and Masuyama, Zeitschr. f. Biologic, 39; Stepanek, Centralbl. f. Physiol., 

 18, 188; Wohlgemuth in Salkowski's Festschrift and Zeitschr. f. physiol. Chem., 44. 



