OVUM. 597 



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 l ), purine bases (MESERNITZKI 2 ), 

 glucose in very small quantities, and mineral bodies. The occurrence of 

 cerebrin and of granules similar to starch (DARESTE 3 ) has not been posi- 

 tively proven. 



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 4 ) . 



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 

 that the lecithin is chemically united with the vitellin (HOPPE-SEYLER 5 ). 

 According to OSBORNE and CAMPBELL, the so-called ovovitellin is a mix- 

 ture of various vitellin-lecithin combinations, with 15 to 30 per cent of 

 lecithin. The protein substance freed from lecithin is the same in all 

 these compounds and has the following composition: C 51.24, H 7.16, 

 N 16.38, S 1.04, P 0.94, O 23.24 per cent. These figures differ somewhat 

 from those obtained by GROSS for vitellin prepared by another method 

 (precipitation with [NH 4 ] 2 SO 4 ), namely, C 48.01, H 6.35, N 14.91-16.97, 

 P 0.32-0.35, S 0.88, and the composition of ovovitellin is theretore not 

 positively known. Besides the vitellin GROSS found a globulin coagulating 

 at 76-77 C. in a solution containing salt, and PLIMMER 6 found a protein 



1 Ueber Ptomaine, Berlin, 1885. 



2 Mesernitzki, Biochem. CentralbL, 1, 739. 



3 Compt. rend., 72. 



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

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



5 Med. chem. Untersuch., 216. 



8 Osborne and Campbell, Connecticut Agric. Exp. Station, 23d Ann. Report, New 



