EPITHELIAL AND ENDOTHELIAL TISSUE. 319 



about the same diameter in all directions j while the columnar 

 epithelia are elongated in one direction viz., that vertical to 

 the subjacent connective tissue. The cement-substance com- 

 pletely envelops the body of the epithelium. 



Columnar epitJielia have two sub- varieties viz., ciliated epi- 

 thelium,witln. moving, hair-like prolongations on the outer surface, 

 and Vacillated epithelium,, provided with motionless, short, deli- 

 cate rods, such as are found in the intestinal canal and the bile- 

 ducts. 



Columnar, ciliated epithelia usually occur in single layers ; 

 sometimes, however, the plastids inserted between the feet of the 

 columnar epithelia are so numerous, and the wedged formations 

 so regularly arranged, as to give the appearance of stratified 

 columnar, ciliated epithelium f. i., in the larynx, the trachea, 

 the larger bronchi, the mucosa of the nasal cavities. The basis 

 of the epithelial body i. e., the broadest outer surface is sup- 

 plied with delicate bent hair-like formations, which, during life, 

 and for a short time after the removal of the epithelia from the 

 body, have a waving motion, in a direction corresponding to the 

 concave side of the hairs. Max Schultze has observed that the 

 cilia penetrate the investing shell of the cement-substance, and 

 are visible in the interior of the epithelium. Th. Eimer and E. 

 Klein have demonstrated that the cilia, penetrating the outer 

 shell, are in connection with the net- work within the epithelium. 

 This fact I can fully corroborate. It explains the motion of the 

 cilia in a satisfactory manner. The reticulum during life is 

 never in perfect rest, and as each hair is attached to the reticu- 

 lum by its short arm, while the long arm projects freely, the 

 horny cement- substance representing the fulcrum of the lever, 

 a slight pull on the short arm must result in a marked extension 

 of the free long arm. This excursion will be most evident in the 

 direction of the concavity of the cilium, each one being slightly 

 curved. It also becomes explicable why liquids, slightly stimu- 

 lating the living matter, increase the motion of the hairs, and 

 make them move actively, even after they have become appar- 

 ently inert. This delicate motion in one main direction is of 

 importance in carrying foreign bodies or secretions outward, and 

 other substances inward. The motion in the air passages f. i., 

 tending upward will greatly assist in the elimination of mucus, 

 which, collecting on the most sensitive portions of the larynx, 

 the inner surface of the posterior wall, and the under surface of 

 the vocal bands, produces reflex action, such as hawking, cough- 



