Embryology, with the physiology of generation ... / Translated from the German, with notes, by William Baly ... From Müller's Elements of physiology and supplement.

  • Johannes Peter Müller
Date:
1848
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Licence: Public Domain Mark

Credit: Embryology, with the physiology of generation ... / Translated from the German, with notes, by William Baly ... From Müller's Elements of physiology and supplement. Source: Wellcome Collection.

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    cal with the formative, vitelline, or embryonic cells of which all the structures of the embryo are originally composed; that they are, in fact, the central cells of the solid mass of which the heart and large blood¬ vessels at first consist. A difference of opinion, however, still exists with respect to the mode in which these original cells are converted into the characteristic corpuscles subsequently found in the blood. According to Vogt, from observations made on the larva of the toad,I (Alytes ohstetricans,) and on the embryo of the salmon (Coregonus palteaj), the cell-wall of each original cell gradually disappears, and the liberated nucleus, in which a secondary nucleus is subsequently formed, becomes the true nucleated hlood-corpuscle. The circumstances which he urges in favour of this view are, first, the close correspondence in size between the nuclei of the original cells and the true corpuscles of the blood; and, secondly, the non-existence of a nucleus at first in the small corpuscles, and its appearance subsequently. Against this view it is objected, by MM. Prevost and Lebert,§ from observations also made on Batrachians, that there is by no means so close a resemblance in size between the nuclei of the primitive cells and the corpuscles of the blood, as stated by Vogt, but that the size of the latter more nearly corresponds with that of the cells themselves: and that, contrary to Vogt’s statement, a nucleus may be detected in the blood-corpuscle in all the phases of its evolution. According to these observers, the blood-corpuscles result from a direct transformation of the cells themselves, which assume an ellipsoid instead of their previously round form, become flattened, lose their granular matter, and acquire coloured contents. Kolliker, also, is opposed to the account given by Vogt, and is of opinion with Prevost and Lebert, that in Batrachians, and also in Mammalia, the embryonic cells themselves are directly transformed into the true blood-corpuscles. Like Prevost and Lebert, he also was unable to find non-nucleated corpuscles in the blood of larval frogs, and of the earliest embryos of Mammalia. A similar view to that of the last three named observers concerning the direct origin of the earliest blood-corpuscles from the em¬ bryonic cells, appears to be entertained also by most other physiologists.^! The conversion of embryonic cells into true blood-corpuscles, in what¬ ever way effected, is probably completed very shortly after the formation of a cavity in the heart and in the large blood-vessels in connection with * Entwickelungs-geschichte der Gebiirtshelferkrote, p. 70. + In Agassiz’s Hist. Nat. des Poissons d’eau douce, tome i. p. 203. J An. des Sc. Nat. 1844, p. 212. § An des Sciences. Nat. 1846, p. 43. || Mr. Macleod (London and Edinb. Monthly Journ. of Med. Sc. Sept. 1842,) is of opinion, however, that in the chick the earliest blood corpuscles are developed from minute dark spherical granules of which alone the blood at first is composed. He believes that each of these possesses the power of enlarging, and being developed into a circular nucleated cell, which subsequently flattens, assumes colouring matter, grows oval, and thus becomes a true red blood-corpuscle.
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