6 SPECIAL HISTOLOGY. 



nucleus. In the smallest cells the nuclei measure from 0002 — 

 O-003'", they are elongated or round, and usually without any 

 distinct nucleolus j in the polygonal cells, there are invariably 

 one or two beautiful, clearly vesicular, usually spherical nuclei, 

 of 0004 — 0005'" with clear contents, and 1 — 2 nucleoli ; 

 finally, in the plates, the nuclei have begun to retrograde, are 

 smaller, 0*004 — 0-006'" long, 0*002 — 00015'" broad, generally 

 flattened and more homogeneous, without any distinct cavity 

 or nucleolus, or containing instead several granules. With 

 respect to its chemical relations, the pavement epithelium of 

 the mouth agrees, so far as we know, in all essential points with 

 the mucous layer of the epidermis, and with the deepest layer of 

 the horny lamina, particularly in the circumstance, that even 

 the plates readily swell up in alkalies; the reader may therefore 

 be referred to § 45. 



[The most essential physiological characters of the epithelium 

 of the oral cavity are, the continual change to which it is sub- 

 jected, and its relations as regards absorption and secretion. 

 With respect to the former, it may be said that the epithelium 

 undergoes a continual desquamation, which, however, does not 

 here, any more than in the epidermis, appear to be the effect 

 of special vital energies in the mucous membrane, or in the 

 epithelial cells, but rather to result from the manifold mecha- 

 nical disturbances to which the surface of the oral mucous mem- 

 brane is subjected during mastication and speaking. On the 

 one hand, these disturbances give rise to a constant detachment 

 of the uppermost plates; and on the other, an uninterrupted 

 regeneration of the lost parts takes place, a process which I 

 am disposed to interpret in this case exactly as I have done in 

 § 46, for the epidermis, and in § 64, for the hairs. As regards 

 the exact mode of that growth of the oral epithelium, which, 

 from what has been said, must perhaps, always be going on in 

 one part or another, we invariably find, upon the surface of the 

 epithelium, during and after very copious desquamation, large, 

 completely flattened cells (which, of course, possess no power 

 of multiplication), never younger and smaller structures, and, 

 therefore, the reparation of any loss cannot take place by the 

 formation of new cells at the surface of the epithelium ; on 

 the contrary, everything indicates that the renewal occurs in 



