274 THE PHYSIOLOGY OF REPRODUCTION 



Liebermann records a loss of nitrogenous substances in his 

 analysis of hens' eggs at various stages of development ; but as 

 Hasselbalch l pointed out, this loss is accounted for by the egg- 

 membrane, which is left behind when the chick is hatched, and 

 which was not included in Liebermann's analysis. 



Reference has already been made to nitrogenous consti- 

 tuents of the yolk : the two phosphoproteins vitellin and live tin. 

 The other protein substances of the white of the egg can be 

 distinguished according to their reactions as albumens, globulins, 

 and a substance behaving like a peptone in so far as it is not 

 coagulated by heat and not precipitated by ammonium sulphate or 

 by hydrochloric and acetic acids. According to the investiga- 

 tions of Morner, 2 this substance is a true glucoprotein and belongs 

 to the mucoid substances. It has, therefore, received the name 

 Ovomucoid. On boiling with hydrochloric acid it yields 34 per 

 cent, of glucosamine. 3 The amount of ovomucoid present in the 

 white of the egg is about 10 per cent, of the proteins ; 6 per 

 cent, of the proteins belong to the globulin group, the remainder 

 being the albumens. All the proteins of the white of the egg, 

 not only the ovomucoid, are exceptionally rich in the carbo- 

 hydrate radicle, and on boiling with dilute hydrochloric acid 

 yield considerable quantities of glucosamine. The albumens 

 and globulins contain about 10 per cent, of glucosamine. This 

 explains perhaps the almost complete absence of carbohydrates 

 in the egg. It acquires further significance from the fact that 

 the developing tissues of the embryo are very rich in mucin, a 

 protein containing considerable quantities of glucosamine. 



The globulin fraction of the egg-white has not yet been 

 studied in detail. It is probable that it is a mixture of several 

 globulins. 



The investigation of the albumen fraction has been greatly 

 facilitated by the work of Hofmeister 4 and Hopkins, 5 which 



1 Hasselbalch, " Uber den respiratorischen Stoffwechsel des Hiihner- 

 embryos," Slcandinav. Arch. f. Physiologic, vol. x., 1900. 



2 Morner, " Uber die im Hiihnereiweiss in reichlicher Menge vorkonimende 

 Mucinsubstanz," Zeitschr. f. physiol. Chemie, vol. xviii. 



3 Quoted from Ergebnisse der Physiologic, vol. i. , Part I. 



4 Hofmeister, " Uber Kry stall isation des Eialbumins," Zeitschrift fur 

 physiolog. Chemie, vol. xiv., 1890, and vol. xvi., 1892. 



5 Hopkins and Pinkus, " Observations on the Crystallisation of Proteids," 

 Journal of Physiology, vol. xxiii., 1898. 



