EPITHELIOID NEW FORMATION. 



surface of mucous membranes along with the epithelium 

 in such a way, that no real difference was to be per- 

 ceived between the two classes in their earliest stages, 

 and that the mucus-corpuscles must therefore in some 

 sort be looked upon as epithelial cells that had gone 

 astray, as children that had turned out ill, that had been 

 impeded in the progress of their development by some 

 early disturbance, but really were intended to become 

 epithelial cells. Unfortunately the notion was then and 

 long afterwards prevalent, that epithelium like all other 

 tissues was normally developed out of a blastema. It 

 was, you know, imagined that on the surface of every 

 mucous membrane in the first instance there transuded a 

 plastic fluid from the vessels running to the surface, and 

 that the epithelial cells were formed out of it. Schlei- 

 den's theory was steadfastly adhered to, that nuclei first 

 form in a fluid, and that membranes do not develop 

 around them until afterwards. At present, however 

 much the different surfaces presented by the skin and. 

 the mucous and serous membranes are examined, the 

 conviction is everywhere unmistakeably acquired, that, 

 the cellular elements extend down to the very surface of 

 the connective tissue, and that there is nowhere a spot, 

 where free nuclei, blastema or fluid exist, but that on. 

 the contrary it is especially the deepest layers which 

 contain the most densely crowded cells. If, at the time 

 when Henle made his investigations, it had been known, 

 that no blastema ever exists in these parts, and that no- 

 development de novo ever takes place there, but that 

 the epithelial cells there present must have been deve- 

 loped either from old cells or from the connective tissue 

 underneath them, he too would certainly also have 

 come to the conclusion, that mucus- or pus-corpuscles 

 which are not furnished by an ulcerating surface (which, 

 would of course be destituc of epithelium) must be- 



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