Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/77

GERMINAL MEMBRANE. a milk-white colour to the fluid. These granules, which are of various size, resemble milk-globules, and, as has been frequently remarked by others, exhibit also like them a brisk molecular motion. In consequence of the speedy action of water upon these globules, they must be examined in albumen or a weak solution of common salt, which preserves them better. These fluids also do not impart a white colour to the surface of a yelk which is opened in them, as water does. The globule, when crushed under the compressorium, tears somewhat suddenly on one side, the other margins remaining smooth, and then, without any increase of the pressure, a large quantity of the globules contained in it flow slowly forth. This fact indicates an external membrane belonging to the globules, but it must be a very soft and delicate one. Baer, who distinguishes four kinds of them, believes that he has also sometimes seen such a mem- brane in the yelk-globules of immature ovarian eggs. The yelk-globules when isolated are round, but, in their natural position in the yelk, they flatten against one another into angular shapes, in which manner the crystal-like bodies observed by Purkinje in the boiled yelk are produced. These bodies generally make up the whole of the true yelk-substance of a fresh egg, so that, with the exception of the contents of the yelk-globules, we do not usually meet with any free granulous substance in the yelk. The minutely granulous substance which is observed in addition to the yelk-globules, particularly after the action of water upon them, appears in most instances, and on the external layers of the yelk invariably, to be produced solely by the destruction of the yelk-globules. In the vicinity of the yelk-cavity of a boiled egg, however, we frequently find a coagulated substance composed of granules similar to those contained in the yelk-globules, and which appears to be actually free yelk substance not enclosed within globules.

It is necessary to examine the eggs while still contained in the ovary, if we wish to become acquainted with the process of formation of these two kinds of globules (those of the yelk- cavity and yelk-substance), and the mode of production of the yelk-cavity and its canal. The younger eggs, having a diameter of one or two lines, have a grayish-white colour, but are not yellow ; if such an one be cut through the centre, under water, it is found to contain a thick, semi-fluid, grayish-white mass,