46 



POULTRY DISEASES 



tective coat. The shell consists largely of lime salts. An outer 

 shell membrane is located just inside the shell and an inner 

 membrane dips across at the large end of the egg, forming 

 the air cell. This membrane consists of a fibrous structure, 

 the fibers of which extend in all directions. The air chamber 

 becomes larger as incubation goes on, in order to meet the 

 respiratory needs of the emljryo or as we may say the fetus, 

 the head being almost invariably developed in that end if the 

 egg lies on its side. The albumen and a portion of the yolk 

 become appropriated for the formation of the embryo chick. 



Immediatel}^ surrounding the yolk there is a dense layer of 

 albumen and outside of this a less dense layer. 



In the allium en at either pole of the yolk is a long mass of 

 dense and partially twisted albumen apparently adherent to 

 the vitelline mem])rane or volk sac, and to the inner shell 

 membrane by the other end. B}^ some this has been regarded 



as a stay, so to 



h 



fi Q 



\ 



speak, which to a 

 certain extent pre- 

 ^^ents violence to the 

 delicate structures 

 within the central 

 part of the egg. 



The albuminous 

 portion {egg white) 

 consists of 86.2 per 

 cent Avater, 13 per 

 cent protein, 0.2 

 per cent fat and O.H 

 per cent ash and 

 possesses a caloric 

 value of 1,608. The 

 egg yolk consists of 

 16.1 per cent pro- 

 tein, 33.3 per cent 

 fat, 1.1 per cent 

 ash and 49.5 per 

 cent water, with a 

 caloric value of 265. 

 The hen egg corresponds to the oxuin of higher animal life 

 where after fertilization of the ovum development of the fetus 

 takes place normally in the uterus of the mother. The ovum of 

 mammals is made up of a male and a female pronucleus as in 

 the hen egg and protoplasm and deuto])lasm, the deutoplasm 

 being nutriment for the em])ryo till it has developed suffi- 

 ciently to draw on the nutriments of the blood from th3 



Fig. is. Diagrammatic Structure of the Egg. 



a, the blastoderm; b, the shell; c, the outer shell 

 membrane; d, the inner shell membrane; e, the air 

 cell at the large end; f, the all)umen; g, the chalaza; 

 h, the dark yolk; i, the white yolk; j. the vitelline 

 membrane; k, the flask-like white yolk; 1, a fluid 

 all)uminous layer wliich immediately surrounds the 

 yolk. 



