117 



The yolk is also insipid, but has a bland oily taste ; and 

 when agitated with water, forms a milky emulsion. When 

 boiled it becomes a granular solid, and yields by expression 

 a yellow insipid fixed oil. It consists of four constituents, 

 water, oil, albumen and gelatine ; on the presence of the 

 albumen depends the hardness of the boiled yolk. 



The air cell is a circular space left between two layers of 

 the external membrane at the larger end of the egg, and is 

 supposed to be designed for the respiration of the chick. 



Dr. Paris in a valuable paper on the Physiology of the 

 Egg, in 10th vol. Lin. Trans, says, 



" I have uniformly found that the folliculus aeris is of 

 greater magnitude in the eggs of those birds which place 

 their nests on the ground, and whose young are hatched, 

 fledged, and capable of exerting their muscles as soon as 

 they burst from their shell, than in the eggs of those whose 

 uests are generally built on trees, and whose progeny are 

 born, blind and forlorn. Thus the folliculi in the eggs of 

 fowls, partridges, and moor hens are of considerable extent, 

 whilst those in the eggs of crows, sparrows and doves are 

 extremely contracted ; the chick, therefore, of fowls and 

 partridges have a more perfect plumage, and a greater apti- 

 tude to locomotion, than the callow nestlings of doves and 

 sparrows. 



It is curious to observe a bird on its perch and at rest ; 

 it is not by any voluntary action which it exerts by which it 

 is prevented from falling when asleep ; it is by the pressure 

 of the body upon the legs by which the flexor tendons of 

 the feet are compelled to embrace the branch upon which 

 it is seated. 



For a new method of rearing poultry to advantage, see 

 the 25th vol. of the Trans, of the Society of Arts. 



