20 TISSUES AND ORGANS 



careful examination, preferably of serial sections, that it is 

 possible to determine an even closer relationship. It can be seen 

 that many of the endothelial cells contain in their cytoplasm 

 extremely tenuous argentaffin fibrils, which, in single sections, 

 usually appear to be nothing more than disconnected fragments. 

 In serial sections it is possible to see that the fragments are not 

 simply an inchoate collection of bits of argentaffin material ; they 

 are indeed fibrils, which seem to emerge from the cells to ramify in 

 the adjacent tissue. It is not clear whether naked argentaffin fibrils 

 leave the cells or whether they split away from the main mass of 

 cytoplasm with an investment of the cell body around each fibril. 

 What is clear, however, is that the scanty fibrils of the earlier 

 stage of Hodgkin's disease are direct derivatives of the endo- 

 thelium. Further examination reveals that there is still another 

 source of the fibrillar material. In addition to the endothelial 

 elements there are also a fair number of elongated reticular cells 

 of the type that normally form part of the boundary of the 

 lymphatic sinuses. Inside these elements there are also argentaffin 

 fibrils, which are more easily visible than are those of the endo- 

 thelial cells. It is, however, not clear that these intra-cellular 

 structures emerge from the cell body ; it seems more likely that 

 they extend all along the ramifications of the elongated processes 

 of the cell without stretching into the tissues in the vicinity. 

 Lastly, the giant cells also show a close relationship to the argen- 

 taffin fibrils. The irregular processes of these large elements 

 contain argentaffin material which seems to emerge from the cells 

 and twine among the neighbouring elements. There seems to be 

 no doubt that the late or so-called fibrotic stage of the malady is 

 caused by a conversion of the predominantly endothelial structure 

 into a reticular one. In other words, whatever the objection to 

 the term " reticulo-endothelium," there are distinct advantages 

 about the name, because it so clearly implies the close relationship 

 of the two forms of histiocytic cell and also suggests their demon- 

 strable interchangeability. In this connection reference may be 

 made to certain of the changes occurring when foreign bodies are 

 present in living tissues ; if these be sterile there occurs a com- 

 pletely aseptic form of inflammation in which the activity of 



