Iviii 



CILIATED EPITHELIUM. 



Fig. XXVII. 



Fig. XXVII. CELLS OP INTESTINAL EPI- 

 THELIUM OF BABBIT, TREATED WITH 

 WATER ; MAGNIFIED 350 DIAMETERS. 

 1 and 2 show striated or porous border, 



somewhat swollen by imbibition; a, b, 



pellucid drops of mucus which have escaped 



from the cells (from Kolliker). 



way by which it might be conveyed from the cells into the lacteal vessels ; but 

 hitherto the search has not been successful. The alleged communication of the cells 



in question with lacteal vessels, through 

 the intermedium of connective-tissue- 

 corpuscles, rests on no sufficient evi- 

 dence. It is true that processes, like 

 roots, have in some cases been observed 

 running down from columnar cells into 

 the subjacent tissue, and in the epithe- 

 lium of the olfactory membrane these 

 radical processes are long and ramified ; 

 but the connection of these prolongations 

 with connective-tissue-corpuscles is as 

 yet a matter of presumption only ; 

 although there is proof of such con- 

 nection in the case of some ciliated 

 epithelium-cells; and it is material to ob- 

 serve that the intestinal epithelium, 

 when examined fresh and without the 

 aid of condensing reagents, shows no 

 such processes. 



The particles of columnar epithelium are undoubtedly subject to shedding and 

 renovation ; but although various suppositions have been hazarded as to the mode in 

 which this is effected, it must be admitted that no satisfactory account has been given 

 of the process. According to Donders and Kolliker, the columnar cells on the villi 

 appear occasionally to cast off a part from their upper end, with subsequent repara- 

 tion of the loss. That is, a cell enlarges and a second nucleus appears ; the upper and 

 broader part, with one nucleus and much of the cell-contents, separates, and the lower 

 remaining portion, with its nucleus, grows again to the natural size. The extruded 

 portion is supposed to become a mucus-corpuscle. 



Spheroidal Epithelium. Tn this variety, the cells for the most part retain 

 their primitive roundness, or, being flattened where they touch, acquire a 

 polyhedral figure, in which no one dimension remarkably predominates. 

 Hence the above term was applied to this form of epithelium by Mr. 

 Bowman. But in some places the cells show a tendency to lengthen into 

 columns and in others to flatten into tables, especially when this epithelium 

 approaches the confines of one or other of the preceding varieties ; in such 

 cases it has been named transitional ; moreover, when the scaly and columnar 

 varieties border upon one another, the figure of their particles is gradually 

 changed, presenting various intermediate forms ; 

 in other words, the epithelium there puts on the 

 transitional character, though it may be only 

 for a very small space. 



The spheroidal epithelium is found in the 

 excretory ducts of the mammary, perspiratory, 

 and of many mucous glands, and a modification 

 of the spheroidal epithelium lines the inmost 

 secreting cavities, or commencing ducts of 

 glands generally (fig. xxvm.). In this last- 

 mentioned situation, where it is sometimes dis- 

 tinguished by the name of glandular epithelium t 

 the nucleated cells contain a large proportion of 



fine granular matter ; in some cases even, the peculiar ingredients of the 

 secretion may be recognised in them ; and it is conceived, that they have a 

 considerable share in preparing or separating these matters from the blood. 

 Ciliated Epithelium. In this form of epithelium, the particles, which are 



Fig. XXVIII. 



Fig. XXVIII CELLS FROM 



THE LlVER MAGNIFIED (Dr. 



Baly). 



