152 MANUAL OF HISTOLOGY. 



Simple ciliated cells are also met with covering the mucous membrane 

 of the female generative apparatus from about the middle of the neck of 

 the uterus up to the free edge of the fimbria. 



Again, in the male, the vasa e/erentia, coni vasculosi, and the passage of 

 the epididymis, down to about its middle, are clothed with similar cells, 

 which become larger and support longer cilia as we advance downward 

 (Becker, KolUker). 



In the new-born child it would appear the cavities of the brain and 

 spinal cord still possess throughout a lining of ciliated cells. This is only 

 partially the case, however, in the adult. Thus, we find these cells in the 

 central canal of the cord, at the posterior end of the fourth ventricle, in 

 the aquceductus Silvii, and in the lateral ventricles. The remaining parts 

 of these regions are lined by simple pavement epithelium of more or less 

 rounded cells, in the adult individual. The plexus clwroidei and telce 

 choroidcee are covered by that modified rounded pavement epithelium men- 

 tioned already in an earlier section ( 88), though in the embryo they are 

 clothed with ciliated cells. 



In conclusion, we find a stratum of flattened epithelium cells, arranged 

 simply or in layers, and covered with cilia, in the Eustacldan tube and 

 cavity of the tympanum, which gives way on the surface of the latter, 

 however, to a niultilaminar pavement epithelium. 



Pigmentary ciliated cells are unknown. Ciliated epithelium appears 

 to possess a limited physiological power of renovation. " Goblet-cells " 

 are frequently met with among them (Schulze). 



94 



Any chemical examination of epithelium to meet adequately the require- 

 ments of present day histology would have to undertake the analysis of 

 cells and intercellular substance, as well as that of the nucleus, body, and 

 envelope of the latter, should it be present. It would have to show also 

 what the changes in chemical constitution are which the young cell 

 passes through in laminated epithelium, while undergoing transformation 

 into the scale-like formations of the older and more superficial layers. 



But these theoretical requirements cannot be responded to, in that we 

 possess no means of isolating the several portions of epithelial tissue from 

 one another, and can only subject the whole mass in the form of a mix- 

 ture to analysis. In spite of all this, however, so much is certain, that 

 epithelium is a tissue which, in its simpler forms and younger layers, is 

 made up of cell-bodies, consisting frequently of protoplasm, while in 

 epithelia of greater thickness the superficial layers undergo chemical 

 transformation to a considerable degree, owing to which they become 

 hard, dried, and more consistent, i.e., become converted into corneous 

 matter or keratin ( 14), or. as the saying is, become horny. 



Many non-laminated pavement epithelia, together with cylinder and 

 ciliated cells, display the ordinary characters of elements formed of unstable 

 protoplasm, the action of water even causing changes in the cell, such as 

 puffing, expulsion of spherical drops, and bursting of the envelope. On 

 the other hand, numbers of simple pavement epithelia resist the action 

 of both cold and hot water, and are affected only by acids and alkalies, 

 earlier or later, after which the protoplasm is changed, though a portion 

 of it may remain unaltered around the nucleus. The latter usually offers 

 a determined resistance to the action of acetic acid. 



The bearing of the deeper or younger cells of laminated epithelia agrees 



