THE RKTICULO-KNDOTHELIAL SYSTEM 89 



Maim and Higgins suggest that the reactions to vital dyes of 

 the fibrocytes and ordinary vascular and lymphatic endothelium 

 are so slight that these two groups could well be eliminated. Jaffe 

 reviews the various theories that have been offered to explain vital 

 staining. It is evident from his discussion that there is great dif- 

 ference of opinion. A concept that is held by Hadfield and Garrod 

 and many others is that vital staining consists of phagocytosis and 

 concentration of the colloidal dye particles and that it differs from 

 simple staining in this respect and also in that the process of os- 

 mosis is not involved as it is in simple staining. It should also be 

 added that the living nucleus is not stained in vital staining. 



According to Hadfield and Oarrod (1938) the discovery that the 

 cells of the reticulo-endothelial system come from undifferentiated 

 mesenchyme and that there is actually present in the tissues of the 

 adult, ancestral cells of the embryonic mesenchyme having toto- 

 potentialities should be credited to Maximow. 



The undifferentiated mesenchyme in adult tissues is described as 

 a cell syncytium in which it is difficult to make out cell boundaries. 

 The cytoplasm of the syncytium is pale and slightly neutrophilic. 

 The nuclei are pale, but there is usually no nucleolus. Hadfield 

 and Garrod say that in the unstimulated organ the cell syncytia 

 are inconspicuous and lie on the basement membrane of the lymph 

 or blood sinuses. When the cells are stimulated, they swell and de- 

 velop a cell outline. Such cells are called reticulum cells (Plate III, 

 Fig. 4), and it can be established that they can be divided into tAvo 

 types only, the so-called littoral cell that does not contain ar- 

 gyrophil fibrils in the resting state while the other does. Both cells 

 may free themselves from the sinus walls and become motile 

 histiocytes (Plate III). These have been called polyblasts by 

 ]\[aximow, macrophages hy Metchnikoff, and clasmatocytes by 

 Ranvier and others. Downey's Handbook of Hematology'^ contains 

 splendid chapters on the fibroblasts and macrophages and on the 

 fixed s^-stem of histiocytes in the liver by Bloom (1938) and 

 Mann and Higgins (1938), respectively, while Jaffe gives an ex- 

 cellent discussion of the reticulo-endothelial system. The supra- 

 vital method of studying blood cells is well presented by Cunning- 

 ham and Tompkins (1938). 



It should be remembered tliat there are conflicting theories held 

 regarding the origin of cells found in the peripheral circulation 



♦Paul B. Hoeber, Inc., Xew York, 1938. 



