I.] THE WHITE YOLK. 5 



which, again, there is an opacity, varying in appearance, 

 sometimes homogeneous, and sometimes dotted. 



The disc is always found to be uppermost whatever 

 be the position of the egg, provided there is no restraint 

 to the rotation of the yolk. The explanation of this is 

 to be sought for in the lighter specific gravity of that 

 portion of the yolk Avhich is in the neighbourhood of the 

 disc, and the phenomenon is not in any way due to the 

 action of the chalaz*. 



A section of the yolk of a hard boiled egg will shew 

 that it is not perfectly uniform throughout, but that 

 there is a portion of it having the form of a flask, with 

 a funnel-shaped neck, which, when the egg is boiled, 

 does not become so solid as the rest of the yolk, but 

 remains more or less fluid. 



The expanded neck of this flask-shaped space is 

 situated immediately underneath the disc, while its 

 bulbous enlargement is about in the middle of the yolk. 

 We shall return to it directly. 



The great mass of the yolk is composed of what is 

 known as the yellow yolk (Fig. 1, y. y). This consists 

 of spheres (Fig. 2, A.) of from 25yLi to 1 00/x' in diameter 

 filled with numerous minute highly refractive granules ; 

 these spheres are very delicate and easily destroyed by 

 crushing;. When boiled or otherwise hardened in situ, 

 they assume a polyhedral form, from mutual pressure. 

 The granules they contain seem to be of an albuminous 

 nature, as they are insoluble in ether or alcohol. 



Chemically speaking the yolk is characterized by the presence 

 in large quantities of a proteid matter, having many affinities 

 with globuhn, and called vitellin. This exists in peculiar associa- 



1 M = -001 mm. 



