24 Th. Lewis, 



Here arises a question of much importance. Are the cells lin- 

 ing the reticulum fibres continous ivith the endothelium cells hounding 

 the sinuses? If so, the two varieties of cell are probably of much 

 the same nature; or in other words, the reticulum cells are nothing 

 more than modified endothelium cells. Careful search has convinced 

 me that such a continuity exists. Cells of the endothelium proper 

 show the appearance of being directly continuous with cells lining the 

 reticulum. Moreover, comparison of the shape and size of the two 

 varieties of cell, lends support to the view that there is one more or 

 less continuous lining for reticulum, capsule and adenoid tissue. The 

 endothelium lining the sinus, and separating it from the adenoid tissue, 

 is nothing more than a layer of endothelium cells, attached to the 

 somewhat denser reticulum fibres found in the outermost part of the 

 adenoid tissue. It appears more striking in this situation, not only 

 because the cells are more numerous, but because of their more regular 

 arrangement, and the fact that there are no cells found lining the 

 neighbouring reticulum fibres in the lymphoid tissue. The endothelium 

 lining the reticulum will probably not form an absolutely continuous 

 lining over it, so that in some places it will be washed by the blood 

 stream. A loss of endothelium cells may occur, either mechanically 

 in the section cutting, or during the living state to form phagocytes. 

 In the reticulum a few scattered involuntary muscle or yellow elastic 

 fibres are met with occasionally, and these have already been obser- 

 ved in the lymphoid tissue. 



If this view of the continuity of the endothelium lining be correct, the 

 blood sinuses may be regarded as nothing more than a coarse capillary 

 meshwork, or they may be looked upon as a system of veins, similar to 

 that described by Böhm und DavidofE^) in the spleen; for the sinus is 

 broken up by strands of reticulum, lined on all sides by endothelium, 

 into a network of short communicating channels, which may be re- 

 garded as short irregular capillaries. I prefer to regard these vessels 

 as capillaries and not venules, as the endothelial lining, bounding them 

 is directly continuous, through that lining the outer wall of the so 



^) Loc. cit. 



