History of the development of the human ovum, with a comparative view of the development of the ova of mammalia and birds / translated and abridged from the German of G. Valentin ... by Martin Barry.

  • Valentin, G. (Gabriel), 1810-1883.
Date:
[1834?]
Catalogue details

Licence: Public Domain Mark

Credit: History of the development of the human ovum, with a comparative view of the development of the ova of mammalia and birds / translated and abridged from the German of G. Valentin ... by Martin Barry. Source: Wellcome Collection.

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

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    a perfectly transparent, pellucid, half-Jtuid and viscid matter, which, after laceration of the membrane of the ovulum, flows out in part more slowly than the layer of granules. It appears through maceration to lose some of its viscidity, and, besides, easily to acquire a more fluid form. 4. Germinal Vesicle always lies close under the membrane of the ovulum, and is generally in part embraced by the layer of granules. Of its existence there can no longer be any doubt, as I have, sometimes alone, sometimes in company with Purkinje, Bernhardt, and others, observed it more than sixty times in the ovula of the most widely different Mammalia; indeed, with the exception of some of those of ruminating animals, I have hitherto sought it in no ovula in vain. But to discover it is not so very easy. That it can be made visible only through compression of the ovulum, we have above stated. One must learn, however, to observe the due degree of pressure, for if it be too weak, nothing is seen, at least not in a decided manner, the vesicle; but if it be too strong, the extremely delicate germinal vesicle bursts, even before the continuity of the outer membrane of the ovulum is de- stroyed, just so as in the smaller ova of birds, the germinal ve- sicle usually bursts before the laceration of the membrane of the yolk. Extremely seldom only, in the ovulum of the Mammalia, does the contrary happen, that the germinal vesicle comes free, and uninjured, out of the lacerated ovulum. I have hitherto had the opportunity for seeing this only three times, and have given a drawing of the appearance of the vesicle, under such circum- stances, in the above-mentioned dissertation of Bernhardt. I re- commend those to whom it is possible to use, besides, an aplana- tic apparatus. If this be provided, the germinal vesicle, with some dexterity and practice in examinations of the kind, can scarcely escape notice. It is, just as in the egg of the bird, a transparent vesicle of a spherical or slightly oval form, and con- sists of a perfectly transparent, homogeneous membrane, and a not less transparent throughout colourless, and non-granulous content, which indeed is itself of more viscid consistence than the diaphanous fluid contained in the centre of the ovulum, though the viscidity of the former does not continue so long as that of the latter. If one succeeds, as in rare cases, in isolating the ger- minal vesicle out of the cavity of the ovulum, one may by fur- ther pressing, burst it, and thus here also separate from one another, its covering and content. The relative size of the ger- minal vesicle seems always to continue nearly the same. The absolute, on the contrary, adapts itself to the absolute size of the ovulum. Thus in the rabbit, where the ovula are relatively smaller than in beasts of prey, I found the germinal vesicle cor- respondingly smaller.