THE EGG. 515 



Protagon contains carbon, hydrogen, nitrogen, oxy- 

 gen and phosphorus. It decomposes below 100, the 

 more readily the more anhydrous it is. When boiled 

 for a long time with baryta-water it yields barium 

 glycerin phosphate, solid fatty acids, and neurine (p. 140). 



Protagon is also contained in blood, in yolk of eggs, 

 and in the vegetable kingdom (e. g. in maize). 



In addition to the substances mentioned, there are 

 contained in the brain protein compounds (particularly 

 casein), cholesterin, lactic acid, inosite, and very small 

 quantities of creatiue, xanthine, sarcine, uric acid, and 

 inorganic salts. 



Other bodies prepared from the brain, and but little 

 known, as cerebrin, cerebric acid, etc., appear to be mix- 

 tures. 



16. The Egg. 



A hen's egg when laid consists of the shell, the 

 white, and the yolk. 



The egg-shell, provided with small pores penetrable 

 by air, is covered on the inside with a solid mem- 

 brane, consisting of two layers, which separate at the 

 larger end of the egg, and leave a space between, 

 which is tilled with air. The shell consists of 97 per 

 cent, of calcium carbonate ; 1 per cent, of calcium 

 phosphate with magnesium phosphate ; and 2 per 

 cent, of organic substance, which remains undissolved, 

 when the shell is treated with hydrochloric acid. 



The white of the egg surrounds the yolk in three 

 layers, of which the outermost is the most liquid. It 

 is inclosed in thin, transparent, membranous cells. At 

 75 it coagulates, forming a solid, white, elastic mass. 

 It contains 12-14 per cent, of albumen, mostly dis- 

 solved in water, as sodium albuminate, besides a very 

 small quantity of fat and grape-sugar, and about 0.7 

 per cent, of inorganic ingredients. These consist of 

 soda, potassium and sodium chlorides, and earthy phos- 

 phates. 



The yolk, inclosed in a thin membrane, appears un- 

 der the microscope as a pulpy mass closely filled with 

 very fine granules, in which yellowish globules and 



