Chap. IV.] 25 



CHAPTER IV. 



ENDOTHELIUM. 



30. THE free surfaces of the serous and synovia! 

 membranes, and of those of the brain and spinal 

 cord, the posterior surface of the cornea and anterior 

 surface of the iris, the surfaces of tendon and tendon- 

 sheaths, the lymph sinuses or lymph sacs of amphibian 

 animals, the cavity of the heart, of blood-vessels 

 and of lymphatic-vessels are lined with a continuous 

 endothelial membrane, composed of 

 a single layer of flattened trans- 

 parent squamous cells, called endo- 

 thelial cells (Fig. 17). Each contains 

 an oval nucleus, situated generally 

 excentrically. Just as in the case 

 of epithelium, the endothelial cell 

 plates are joined by a fluid or semi- 

 fluid homogeneous interstitial or Xa in ce 8 iis! 'anthe 



7 rt , v , r> nucleus of the latter 



cement substance or the nature ot are wen shown, 

 globulin. When examining any of 

 the above structures fresh the endothelial cells are 

 not, as a rule, visible, owing to their great trans- 

 parency ; but by staining the structures with a 

 dilute solution of nitrate of silver, and then ex- 

 posing them to the influence of the light, the cement 

 substance appears stained black, whereby the shape 

 and size of the cell plates become evident. By various 

 dyes also the nucleus of each cell plate may be brought 

 into view. 



On careful examination, and with suitable re- 

 agents, it can be shown that each endothelial cell 

 consists of a homogeneous ground-plate. In it 



