The elements of embryology / by M. Foster and the late Francis M. Balfour ; edited by Adam Sedgwick and Walter Heape.

  • Michael Foster
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: The elements of embryology / by M. Foster and the late Francis M. Balfour ; edited by Adam Sedgwick and Walter Heape. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

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    THE WHITE YOLK. 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 which is in the neighbourhood of the disc, and the phenomenon is not in any way due to the action of the chalazae. 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 25//. to lOO//,1 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 globulin, and called vitellin. This exists in peculiar associa- 1 m = -001 mm.
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