396 



COMMERCIAL POULTRY RAISING 



Texture of Shell. — It will be noted that the- shell of an egg is 

 exceedingly porous, which enables the embryo to take in oxygen 

 through the shell, otherwise it could not breathe. See Fig. 256. 

 During the early stages of incubation a network of blood-vessels 

 surround the inner membrane of the egg, close to the shell. See 

 Fig. 257. These blood-vessels absorb the oxygen and act as the 

 respiratory apparatus for the embryo until about the nineteenth 

 day of incubation, when the lungs are completed and brought 



into use. The oily secre- 

 tion deposited on the shell 

 in the cloaca tends to stop 

 up the pores temporarily, 

 so as to prevent undue 

 evaporation of the con- • 

 tents of the egg, and to 

 keep the pores clear. Ob- 

 viously, a hatching egg 

 should not be washed; 

 and if very badly soiled it 

 should not be used for 

 hatching purposes at all. 

 To return to the yolk, it 

 must be very apparent 

 that if production is to be 

 successfully carried out, 

 the yolk or ovum,which is 

 the real beginning, must be carefully and normally developed, 

 otherwise the succeeding processes are all thrown out of kelter. 

 Egg making is a very exhaustive process, if we stop to consider that 

 a profitable hen is expected to lay about 150 times a year, which 

 is equivalent to almost five times her weight; hence the drain 

 on her system is enormous. The activity of the ovary, then, 

 depends upon the health of the bird. 



The over-fat hen does not lay because over-fatness is an indi- 

 cation of improper or immoderate feeding, usually accompanied 

 by lack of exercise. The poor, anemic, emaciated hen cannot 



Fig. 258. — Sectional view of fowl's egg. 



1, Yellow yolk composed of successive layers; 



2, vitelline membrane; 3, layers of albumen 

 (white) ; 4, two layers of the lining mem- 

 brane of the shell; 5, calcareous shell; 6, 

 chalaza ; 7, air space between the two layers 

 of the shell membranes; 8, cicatricula, with 

 its nucleus, beneath which is seen the canal 

 leading down to the white yolk cavity, or 

 latebra, 9. 



