TFIE RKTICULO-KNDOTHELIAL SYSTE^E 91 



ill health and disease as well as tlic phagocytic cells of the tissues 

 and the varioiLs types of cells observed in inflammatory exudates. 

 The monopkijletic theory assumes that the embryonic mesenchyme 

 gives rise to a stem cell, called l)y Papi)enheim the lymphoidocyte, 

 which is endowed with in toto-potentialities. The environment in 

 which it finds itself determines the type of cell which develops from 

 it. In contrast to this is the pohjphyletic theory which assumes 

 that the embryonic mesenchyme gives rise to stem cells endoAved 

 with different potentialities : one is destined to give rise to gran- 

 ulocytes, another to lymphocytes, etc., regardless of the environ- 

 ment. 



The adherents of both theories agree that the stem cells originate 

 from cells that are of mesenchymal origin and that the adult 

 mononuclear phagocytic cell of perhaps major importance in the 

 body's defense has a peculiar affinity for trypan blue. The ma- 

 jority of workers are willing to call this cell a clasmatocyte or 

 histiocyte. Sabin et al. formerly (1925) divided the large mononu- 

 clear phagocytes into two groups. One group which has an af- 

 finity for trypan blue she called clasmatocytes. These, she thought, 

 originate intravascularly in the bone marrow, liver, spleen, and 

 lymph glands and migrate into the tissues, to become the tissue 

 phagocytes. The second group, which has little affinity for trypan 

 blue, she called the monocyte. These, she thought, originate ex- 

 travascularly from reticular cells in the same tissues. They enter 

 the blood stream and constitute the monocytes of the peripheral 

 circulation although they too are found in the tissues. More re- 

 cently Sabin (1932) has come to regard the monocyte and clas- 

 matocyte as one and the same cell exhibiting difference in appear- 

 ance as a result of the kind of material it has ingested. The various 

 types of cells found in tlie blood and tissues are illustrated in 

 Plates I, II, and III. 



These show the monocytes and clasmatocytes of Sabin as they 

 appear in supravital preparations where neutral red is used to 

 demonstrate granules and vacuoles and Janus green to stain any 

 mitochondria present. It will l)e observed that the monocyte has 

 a kidney-shaped nucleus with a rosette of neutral red granules in 

 the cytoplasm within the hof of the nucleus. These granules sur- 

 round the centrosphere. The vacuoles containing neutral red are 

 more or less peripherally arranged. The clasmatocyte has an oval, 



