Excerpt from Memoirs of the Wistar Institute of Anatomy and Biology, Vol. 7: An Experimental Analysis of the Origin of Blood and Vascular Endothelium; The Origin of Blood and Vascular Endothelium in Embryos Without a Circulation of the Blood and in the Normal Embryo, Forty-Nine Figures; A Study of Wandering Mesenchymal Cells on Th The origin of blood presents an almost unique problem in embryology. First, on account of the fact that the initial blood anlage in many animals is contributed to by wandering cells. Second, owing to the establishment of an early flow or circulation of embryonic fluids before the blood corpuscles have arisen. Soon after the cells and corpuscles are formed they are swept into this circulating current and carried to all parts of the body. In this way the blood cells become associated and mixed with numerous other types of cells, and it is difficult, if not impossible, to establish their true relationship with their surroundings. For the above reasons one is often ready to believe that many of the even careful and long thought out contributions to the development of blood are, after all, largely a matter of the authors own interpretation rather than a record of the actual processes. The general current of opinion at the present time would seem to indicate that all blood cells arise from a mesenchymal type of cell.
A number of very competent workers have described the change of this mesenchymal cell into a stem cell or mother cell. On one side from this mother cell are developed various leukocytes, which it is important to note always occur in an interstitial position, while on the other hand, this same general type of mother cell gives rise to other cells which later differentiate into typical erythroblasts, and finally erythrocytes which are always found to be located within the vessels. These so called indifferent mesenchymal cells probably, from the evidence contained in the literature, do form blood cells, but to the discriminating reader the evidence is not at all convincing that both white blood cells and red blood cells really arise from one common mother cell or common embryonic anlage. The possibility, and even probability, is certainly present that these so-called stem mother cells may in reality not all belong to one type, but are different and may already be destined to form either red cells or white cells. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work.
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