114 HAITTS OF BIRDS; 



the yolk, which intestine was inferred without proof 

 to have existed previous to fecundation. M. Du- 

 trochet, on the contrary, found that the intestine 

 enters the yolk by a development extended by suc- 

 cessive processes over the whole periphery of the 

 yolk. 



The chemical constituents of these several parts 

 of the egg are as follows. The shell consists prin- 

 cipally of carbonate of lime, similar to chalk, with a 

 small quantity of phosphate of lime and animal 

 mucus. When burnt, the animal matter and car- 

 bonic acid are separated, the first being reduced to 

 ashes or animal charcoal, and the second dissipated ; 

 while lime, mixed with a little phosphate of lime, is 

 obtained. The white is without taste or smell, of a 

 viscid glary consistence, readily dissolving in water, 

 coagulable by acids, alcohol, and water heated to 

 165 Fahrenheit. When it has been thus coagulated, 

 it is no longer soluble in either cold or hot water, 

 and acquires a slight insipid taste. The experiments 

 of Dr. Bostock show that it is composed of 80.0 

 parts of water; 15.5 of albumen; and 4.5 of 

 mucus ; exhibiting, besides traces of soda, benzoic 

 acid and sulphuretted hydrogen gas. The latter 

 we observe on eating an egg with a silver spoon 

 to stain it with blackish purple, by combining with 

 the silver, and forming sulphuret of silver. The 

 yolk possesses an insipid, bland, oily taste, and 

 when agitated with water forms a milky emulsion. 

 When long boiled it becomes a granular, friable 

 solid, yielding by expression a yellow, insipid fixed 

 oil. Its chemical constituents are water, oil, albu- 

 men, and gelatine. In proportion to the quantity 

 of albumen, the egg boils hard. The oil of the yolk 

 is soluble in sulphuric ffither. 



An important part of the egg which we have not 

 hitherto named is the air-bag (folliculus aeris), 



