450 THE GLANDULAR ORGANS. 



It contains albumins, nucleins, lecithins, potassium salts, and possibly 

 also traces of glycogen, though this is doubtful. 



When broken, the yolk constitutes a creamy, viscid material, of 

 an orange-yellow color, which forms an emulsion with water, and is 

 coagulated by alcohol and on boiling. Its reaction is feebly alka- 

 line. On microscopical examination it is seen to consist of innumer- 

 able spherules, some of which are rich in fats and lipochromes, 

 while others, which are smaller, are colorless, transparent, semi- 

 crystalline structures of an albuminous character. In the eggs of 

 certain amphibia and fishes distinctly crystalline bodies are further 

 met with, which are spoken of as yolk platelets, and are analogous 

 to the aleuron granules of seeds. As has already been mentioned, 

 they probably consist of a compound of albumins with lecithins and 

 nucleins. The ichthidin, which is found in carp eggs, and which in 

 amorphous form is known as ichthulin, belongs to this category. 1 

 The same holds good of the ichthin of shark eggs and the emydin 

 of tortoise eggs. 



As I have stated, the yolk of hens' eggs represents about 29 per 

 cent, of the entire weight. Its actual weight may thus vary between 

 8.7 and 20.3 grammes. The general composition of the yolk is seen 

 in the following analyses, which are taken from Gautier : 



Per cent. 



Water 47.19-51.49 



Solids 48.51-42.81 



Fats (olein, palmitin, and stearin) 21.30-22.84 



Vitellin and other albumins 15.63-15.76 



Lecithins 8.43-10.72 



Cholesterin 0.44- 1.75 



Cerebrin 0.30 



Mineral salts 3.33- 0.36 



Coloring-matter ) n KKO 



Glucose / 



Analysis of the mineral salts, calculated for 100 parts of ash, has 

 given the following results (Poleck and Weber) : 



Sodium (Na 2 O) 5.12- 6.57 



Potassium (K 2 O) 8.05- 8.93 



Calcium (CaO) 12.21-13.28 



Magnesium (MgO) 2.07- 2.11 



Iron (Fe 2 O 3 ) 1-19- 1-45 



Phosphoric acid, free (P 2 O 5 ) 5.72 



Phosphoric acid, combined 63.81-66.70 



Silicic acid (SiO a ) 0.55- 1.40 



Chlorine traces 



1 From recent researches of Levene it appears that different forms of ichthulin 

 exist. The ichthulin of carp eggs thus yields a reducing substance on hydrolytic 

 decomposition, while that of the cod apparently contains no carbohydrate radicle. 

 The latter, on treating with alkalies, yields a paranucleinic acid, which is similar 

 to vitellinic acid (see below). Elementary analysis of the two forms has given the 

 following results: Ichthulin of carp eggs (Walter): C, 53.52; H, 7.6; N, 15.63; 

 S, 0.41 ; P, 0.43 ; Fe, 0.10 ; O, 22.19 per cent. Ichthulin of codfish eggs ; C, 52.44 ; 

 H, 7.45 ; N, 15.96 ; S, 0.92 ; P, 0.65 ; Fe and O, 22.58 per cent. 



