W. B. WHERRY 



873 



blood: (i) the oxyphilic, eosinophile granule, which is large, refractive, uniform in size, 

 round as in human blood, or in long rods as in birds; (2) the amphophilic granule 

 which takes either a basophilic or acidophilic dye, and is found only in young cells; 

 (3) the metachromatic basophilic granule of the mast cell; (4) the truly basophilic 

 granule which is not found in human blood; (5) the fine neutrophilic granulation of 

 human blood. 



Studies on the blood since the time of Ehrlich^ have led to a classification of the 

 white cells into three groups: first, the monocytes, with two different types, large 

 mononuclear forms and the so-called "transitional" cell of Ehrlich; second, the leuko- 

 cytes with their three different cells (neutrophile, eosinophile, and mast cells); and 

 third, the lymphocytes. It is believed that there is no transition between the cells of 

 these three main groups. 



There are three strains of cells of the connective tissues which contribute to the 

 blood cells. All of these strains give more cells to the connective tissues than to the 

 blood. 



1. The angiohlasts, giving the endothelium, the erythrocytes, and the monocytes. — The 

 monocyte stem is largely extra vascular, in small part intravascular, giving the histio- 

 cytes which are the monocytes of the blood and the clasmatocytes of the connective 

 tissues. They have developed along the line of the phagocytic power of their parent- 

 cell, endothelium, and are especially differentiated to take up and store particulate 

 matter. It has, I think, become clear that certain endothelial cells, like the Kupffer 

 cell of the liver which is a specialized endothelial cell within the capillaries of the liver 

 anchored out into the blood stream by guy ropes of cytoplasm, and the endothelial 

 cells of the veins of the splenic pulp as well as the endothelium of the splenic sinuses 

 have the maximum power of phagocytosis and that they clear the blood stream of 

 foreign particles within a very few minutes (Sabin).' 



In the circulating blood two types of monocytes are present — the large mononu- 

 clear cell of Ehrlich, which has a large oval nucleus and basophilic cytoplasm, consti- 

 tutes about 0.2 per cent of the white cells; the other constitutes about 6 per cent of the 

 cells and has a nucleus which varies from indented to horseshoe or S-shape, with a 

 basophilic cytoplasm containing azurophile granules. These are the macrophages of 

 Metchnikoff . These are the histiocytes or monocytes of the blood, the endothelial leu- 

 kocytes of Mallory. According to Evans, Mcjunkin, and others, endothelial cells un- 

 der proper stimulation will leave the vessel walls and enter into the circulation. Sabin, 

 in her studies on the growing blood vessels in the yolk sac of the chick, noted a mul- 

 tiplication of the endothelial cells which wander both into the lumen of the vessel 

 (monocytes) and into the tissues (clasmatocytes). 



2. The second strain, the gramdocyte. — From these descend the neutrophile leu- 

 kocyte, the eosinophile leukocyte, and the mast cell. 



a) The neutrophile leukocyte. — In the higher animals these are formed only in the 

 marrow. They originate from a myelocyte which has a round vesicular nucleus and 

 neutrophile granules. These myelocytes are grouped in extra vascular centers in which 

 development occurs from the center so that the mature cells lie at the periphery; these 



' Complete critical reviews by Sabin, F. R.: Physiol. Reih, 2, 38. 1922; Bunting, C. H.: ibid., 

 p. 505; and Foot, N. C: Anat. Rec, 30, 15. 1925. 



