On the source and the course of the embryonic blood circulation during development in the warm-blooded Vertebralia / by W. Macdonald.

  • Macdonald, William, 1797-1875.
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: On the source and the course of the embryonic blood circulation during development in the warm-blooded Vertebralia / by W. Macdonald. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    It is not a little strange that, with these clear views, Harvey should have supported the established theory of the fcetal circulation, so difficult it is for even the most eminent minds to escape the thraldom of prejudice in favour of long- established theory supported by the majority. Had he thoroughly then wrought out his views of the blood and its foetal circulution as al)ove expressed, he would then have capped and culminated his immortal discovery, which is still left an open question as regards the early course of the fcetal circulation. About the middle of the eighteenth century, Caspar Frederic Wolff promulgated in the Petrapolotan Transac- tions, and afterwards separately published in Berlin, his thesis Theoria Gencrationis controverting the evolution theory then prevalent among physiologists. This distinguished author endeavoured to show, by the numerous observations he had made on the development of the chick, that the fecundated egg, previous to incubation, is very simple in structure, and does not contain, as far as by the greatest attention he could discover, any part to be compared to any organ either of the foetal or adult animal, but that the several organs of the chick may be seen gradually forming ah initio by formation of their parts,— carefully avoiding speculation as to the causes of the plienomena which he had observed, as he considered it was the indulgence in theory, without due attention to facts, that those who had preceded him had been led into error. Being aware of the difficulty of disproving by mere argument the assertion made and supported by an opposing party at tliat time, that all the organs of an animal really exist, though their minuteness and transparency render them invisible, in the germ of the egg, he at once endeavoured to establish his own opinions, without directly opposing their hypothesis, by recording those observations in the experi- ments he had made, which seemed to prove the formation of a new part in the egg. Having delayed commencing his experiments beyond the fortieth hour of incubation, the first part he described was the superior mesenteric vascular network lying above the surface of the yolk, but entirely