446 THE GLANDULAR ORGANS. 



termed odcyamn, is composed partly of biliverdin, and is in part a 

 blue derivative of bilirubin. 



The membranes of birds 7 eggs consist essentially of keratin, but 

 contain also a small amount of mineral salts, of which calcium 

 phosphate is the most abundant. 



In fishes and amphibia the egg envelope is represented by a trans- 

 parent gelatinous material, which seems to consist almost exclusively 

 of mucin. In the invertebrates chitin and skeletins take the place 

 of the keratin of birds' eggs, but in some the latter also is found. 



The weight of the shell and membranes in the case of hens' eggs 

 represents about 9 to 11 per cent, of the total weight of the egg, 

 while the albumen constitutes about 60.5 per cent, and the yolk, 

 viz., the ovum proper, the remaining 29 per cent. The total weight 

 of hens' eggs may vary between 40 and 70 grammes. 



The Albumen. The albumen or white of egg, as obtained directly 

 from the raw egg, appears as a faintly yellow, exceedingly viscid, 

 semiliquid material. On microscopical examination this can be 

 shown to consist of compartments, which are limited by very 

 delicate membranes, and enclose the albumen proper. These 

 membranes are continuous with the so-called chalazse and the 

 membranes immediately beneath the shell, and are, like these, 

 composed of keratin. 



The albumen proper may be separated from its membranous con- 

 stituents by pressing the material through a cloth, and then appears 

 as an opalescent fluid, which is only slightly viscid, and can be 

 filtered without much difficulty. Its reaction is distinctly alkaline, 

 and the specific gravity about 1.045. On boiling, it coagulates to a 

 compact mass, which in the case of hens' eggs is entirely opaque. 

 In some birds, however, such as the swallow, the crow, the finch, 

 etc. i. e., in true nesting birds the albumen remains transparent, 

 owing to the formation of alkaline albuminates. Such albumen has 

 been termed tata-albumen. It may be produced artificially by placing 

 hens' eggs in a 10 per cent, solution of sodium hydrate for two or 

 three days, when a gradual diffusion of alkali occurs into the albu- 

 men. On subsequent boiling, this appears like true tata-albumen. 



Analysis of the albumen of hens' eggs has given the following 

 results : 



Per cent. 



Water 80.00-86.68 



Solids 13.32-20.00 



Albumins 11.50-12.27 



Extractives 0.38- 0.77 



Glucose 0.10- 0.50 



Fats and soaps traces 



Mineral salts 0.30- 0.66 



Lecithins and cholesterin traces 



According to Poleck and Weber, the mineral ash has the follow- 

 ing composition, calculated for 100 parts: 



