CHANGES OF THE SUPERFICIAL ENDOTHELIUM. 69 



they are both situated on the surface of the membrane, and one can 

 properly speak only of young endothelium. 



As has been already indicated, the proliferation of the endothelium 

 surrounding a true stoma is an active one. Not only do these endo- 

 thelial cells enlarge, become distinctly granular, and present nuclei 

 in the act of division, not only do these cells germinate and produce 

 lymphoid cells, but this change gradually spreads out on the one 

 hand over the endothelial cells of the surface which are in the 

 neighbourhood, as well as over those of the vertical lymph-canals, and 

 further over those of the lymphatic capillaries into which these lymph- 

 canals open. If we search the abdominal surface of a diaphragm 

 furnished with abundant knots of tubercle, we shall recognise the 

 most various appearances of development as regards the proliferation 

 of the endothelium of the stomata. As the youngest stages, those 

 are most undoubtedly to be taken where the stoma is surrounded 

 by a projecting zone of young endothelial cells at both ends, that is 

 to say, not only at the entrance into the vertical canal, but also at 

 the exit of the latter into the straight lymphatic capillary. 



Besides these, we find other places where this zone has become 

 already several cells high ; this has then the appearance of a short 

 cone. Other stages are these : the cone of cells is longer, and at the 

 same time somewhat thinner and solid ; further, broad, long cones, 

 which, although the stoma is collapsed, still show a central cavity ; 

 and, finally, where only a large and broad patch is to be seen, formed 

 of young endothelial cells. In the latter, the diagnosis that we have 

 to do with a germination of endothelium round a stoma is generally 

 not easy. Sometimes it is rendered easy by the following circum- 

 stances : first, one finds an indication of the opening, close round 

 which the germination-process has become most intense, for the 

 smallest cells are found there ; secondly, if the opening itself be not 

 visible, we can still recognise the spot where the stoma is to be looked 

 for, from the presence of an amorphous central fibrinous plug very 

 darkly coloured in silver. Close to this, the smallest elements lie ; 

 finally, a thick cord of fibrine, which, becoming gradually thinner, is 

 seen to dip into the point around which the smallest elements lie, 

 thus indicating the direction and the place of the current of absorp- 



