26 The Lymphocyte and Lymphocytic Tissue 



slide 1: Stages in the transformation of mesenchymal cells into the first free 

 stem cells and the development of the latter into primitive erythrocytes in the 

 yolk sac and body mesenchyme of several species of mammalian embryos. (A. A. 

 Maximow, Plate XVIII. Reproduced in Bloom. 2 ) 



slides 2 and 3: Various stages in the development of the free stem cells, in 

 the human yolk sac, into primitive erythrocytes, small and medium-sized lym- 

 phocytes, phagocytes, megakaryocytes, and eosinophilic and neutrophilic myelo- 

 cytes. Figure B shows development of primitive and definitive erythroblasts in 

 adjacent foci in a slightly older human yolk sac. (W. Bloom and G. W. Bartel- 

 mez, Plates 1 and 2. 3 ) 



slide 4: Colored photomicrograph of several large stem cells and one medium- 

 sized one in yolk sac of human embryo. 



slide 5: Colored photomicrograph of hematopoiesis in human embryo (70 

 mm.) liver near the capsule. Eosinophilic and neutrophilic myelocytes are inter- 

 mixed with medium-sized lymphocytes, one of which is in mitosis. Nearby are one 

 very large stem cell and a group of polychromatic definitive erythroblasts. 



slide 6: Development of large, medium-sized, and small stem cells in the 

 mesenchyme of primitive bone marrow in embryos of several laboratory mammals. 

 (A. A. Maximow, Plate II. 8 ) 



slide 7: Development of stem cells of various sizes, definitive erythroblasts, 

 and myelocvtes in primitive human embryonic marrow. (A. A. Maximow, Figs. 

 105 and 106>) 



slide 8: Two stages in early human lymph node primordia showing develop- 

 ment of large and many small stem cells (lymphocytes) from mesenchyme. (A. A. 

 Maximow, Figs. 107 and 108.-») 



slides 9-12: Colored photomicrographs of several stages in developing lymph 

 nodes of a human embryo of 70 mm. These formed an important part of the 

 presentation as they showed eosinophilic and neutrophilic myelocytes developing" 

 in moderate numbers in the lymphatic tissue. These granulocytes have nuclei in- 

 distinguishable from those of the surrounding smaller lymphocytes. 



slide 13: Development of eosinophilic and heterophilic myelocytes from small 

 lymphocytes within germinal centers of white pulp of spleen and a nodule of 

 lymph node from guinea pigs. (W. Bloom, Plate l. 1 ) 



slide 14: Colored photomicrograph of three eosinophil myelocytes in human 

 embryonic thymus. 



REFERENCES 



1. Bloom, \Y. The hemopoietic potency of the small lymphocyte. Folia haemal. 

 5 5.122, 1926. 



2. Bloom, \V. "Embryogenesis of Mammalian Blood," in Handbook of Hema- 

 tology, eel. by Downey, H., New York, Paul B. Hoeber, Inc., 1938, vol. 2, p. 865. 



3. Bloom. W., and Bartelmez, G. W. Hematopoiesis in young human embryos. 

 Am. J. Anat. 67:21, 1940. 



4. Downey, H. The structure and origin of mammalian lymph nodes and their 

 relations to endothelium and reticulum. Haematologica 3:431, 1922. 



5. Jordan, H. E. "Comparative Hematology," in Handbook of Hematology, ed. 

 by Downey, H. New York. Paul B. Hoeber, Inc., 1938, vol. 2, p. 699. 



