224 BLOOD 



her of red cells. Giant cells are characteristic elements of all hemapoietic 

 organs. The megakaryocytes protrude long pseudopodia which segment 

 into blood- platelets (Wright), abundantly present in red marrow. 



8. Erythrocytes. These cells include the several developmental 

 forms of red cells : (a) megaloblast, (b) normoblast, (c) erythroblast and 

 (d) erythroplastid. The megaloblast is very similar to the leukoblast ex- 

 cept that the cytoplasm contains a slight amount of hemoglobin, and 

 therefore gives an oxyphilic staining reaction. The nucleus is granular, 

 with a delicate chromatic network. This is the so-called ichthyoid stage of 

 Minot. Normoblast and erythroblast are closely similar stages (sauroid 

 stage of Minot), characterized by the relatively smaller and denser more 

 chromatic nucleus, and a relatively more extensive shell of cytoplasm 

 with increasingly more hemoglobin: The erythroplastid develops from 

 the erythroblast through loss of nucleus, generally by extrusion. 



Evans (Amer. Jour. Physiol., 37, 2, 1915) has directed attention anew to 

 the phagocytic large mononuclear leukocytes, the 'macrophages' of Metsch- 

 nikoff (1892). On the basis of a specific response to vital azo dyes he iden- 

 tifies them as a group distinct from the large mononuclear elements and 

 lymphocytes of the blood, and includes among them certain endothelial and 

 reticular cells and the 'clasmatocytes' (Ranvier) or 'resting wandering cells' 

 (Maximow) of connective tissue,- all of which may become free macrophages. 

 These cells in mammals, of round or elongated shape, range in diameter 

 from about 10 to 30 microns; they contain a stoutly cresentic nucleus of 

 irregular contour and excentric position ; the . cytoplasm is weakly baso- 

 philic, covered with delicate pseudopods of various sizes, and frequently 

 filled with large vacuoles. As endothelial cells they may line the capillaries 

 and venules of the liver (Von Kuppfer cells'), spleen, red bone-marrow, 

 hemal glands, and the lymphatic sinuses of lymph nodes. They include 

 also reticular cells of lymph nodes, spleen pulp and bone-marrow, and the 

 clasmatocytes of connective tissue. As free cells they occur in the serous 

 cavities, lymph sinuses of lymph nodes, spleen and hepatic capillaries. 

 They are abundant in traiisudates and exudates in serous cavities. Only 

 under pathological conditions do they appear in the peripheral blood stream. 

 Weidenreich identified them with the large mononuclear leukocytes of the 

 blood and lymph. Evans' experiments, on the contrary, give no indication 

 that leukocytes are converted into these cells. They originate chiefly from 

 endothelia. They are phagocytes and are active also in the normal physio- 

 logical processes. They handle the blood and bile pigments, and fats and 

 lipoids. The protoplasm of the macrophages is characterized especially 

 by its response to finely particulate matter. Macrophages share the func- 

 tion of phagocytosis with the polymorphonuclear elements of the blood. 



