BY DR. KLEIN. 35 



CHAPTER II. 



EPITHELIUM AND ENDOTHELIUM. 



I 



UNDER this heading are included the epithelium of the 

 mucous membranes, of the cornea and conjunctiva, and of the 

 integument, and the endothelium of the serous membranes. 

 The epithelium-like structures which are in relation with the 

 nerves of the various organs of sense will be examined in Part 

 II. 



Ciliated Cylindrical Epithelium. To investigate cili- 

 ated epithelium in the living state, a frog should be selected, 

 and its mouth opened with the handle of a scalpel. Then, 

 using either a lancet-shaped needle or the blade of a sharp knife, 

 we scrape from the projection in the roof of the oral cavit}', 

 corresponding with the floor of the orbit, a little of its epithe- 

 lial covering. This is transferred to a small drop of an indiffe- 

 rent fluid (half per cent, solution of common salt) on a glass 

 slide, slightly separated with needles, and covered in the usual 

 manner. In such a specimen we find not only masses of epi- 

 thelium in connection, but also smaller groups and single cells. 

 In the masses of epithelium we cannot distinguish quite clearly 

 the individual cells, but on the free border on the coast, as 

 it were, of the epithelial island we observe the exceed iugly 

 lively movement of the cilia. In addition we see blood disks, 

 small round particles of protoplasm and granules driven quick- 

 ]y along in the fluid ; and from tnese passing bodies we are 

 able to recognize the direction of the movement of the cilia, 

 an' observation which could not otherwise be made, on account 

 of the extreme rapidity of that movement. In the smaller 

 epithelial groups we are able more easily to recognize the in- 

 dividual shortly-conical cells. These groups are in more or 

 less rapid rotation, th-; rotatory motion being due to the fact 

 that only one portion of their surface is furnished with cilia 

 that, namely, which corresponds to the bases of the conical 

 cells. 



Effects of Reagents on Ciliary Motion. Dilute 

 Alkalies. After some time we perceive that the cilia here 

 and there begin to strike more slowly, and, by-and-by, they 

 come to rest. In a specimen prepared as above described, 

 which has of course been prevented from becoming dry by the 

 occasional addition of a drop of half per cent, solution of com- 

 mon salt, if we choose a spot at which the ciliary movement 



