HANDBOOK OF PHYSIOLOGY. 



vous system is shown also in its occurrence in the lowest invertebrate 

 animals apparently unprovided with anything analogous to a nervous 

 system, in its persistence in animals killed by prussic acid, by narcotic 

 or other poisons, and after the direct application of narcotics, such as 

 morphia, opium, and belladonna, to the ciliary surface, or of electricity 

 through it. The vapor of chloroform arrests the motion; but it is re- 

 newed on the discontinuance of the application (Lister). The movement 

 ceases when the cilia are deprived of oxygen, but is revived on the 

 admission of this gas. Carbonic acid stops the movement. The contact 

 of various substances, e.g., bile, strong acids, and alkalies, will stop the 



FIG. 24. Epithelium of the bladder, a, 

 one of the cells of the first row ; 6, a cell of 

 the second row ; c, cells in situ, of first, 

 second, and deepest layers. (Obersteiner.) 



FIG. 25. Transitional epithelial cells from 

 a scraping of the mucous membrane of the 

 bladder of the rabbit. (V. D. Harris.) 



motion altogether; but this seems to depend chiefly on destruction of 

 the delicate substance of which the cilia are composed. Temperatures 

 above 45 C., and below C., stop the movement; but moderate heat 

 and dilute alkalies are favorable to the action and revive the movement 

 after temporary cessation. 



As a special subdivision of ciliary action may be mentioned the mo- 

 tion of spermatozoa, which may be regarded as cells with a single cil- 

 ium. 



B. Transitional Epithelium. This term has been applied to cells, 

 which are neither arranged in a single layer, as is the case with simple 

 epithelium, nor yet in many superimposed strata as in laminated ; in 

 other words, it is employed when epithelial cells are found in two, three, 

 or four superimposed layers. 



The upper layer may be either columnar, ciliated, or squamous. 

 When the upper layer is columnar or ciliated, the second layer consists 

 of smaller cells fitted into the inequalities of the cells above them, as in 

 the trachea (Fig. 24, J). 



The epithelium which is met with lining the urinary bladder and 

 ureters is, however, the transitional par excellence. In this variety there 

 are two or three layers of cells, the upper being more or less flattened 

 according to the full or collapsed condition of the organ, their under 



