COLLOIDS, LYOPHOBIC 



veloped system of surface invaginations, 

 reminiscent of tubules, speaks for the fact 

 that structural evidence for micropinocytosis 

 is present. It is, therefore, concluded that the 

 brush cells of the respiratory tract and those 

 of the male reproductive tract are func- 

 tionally different, although the structure of 

 their surfaces is almost identical (Figs. 2, 7). 

 Ciliated cell. The ciliated cells have a 

 cytoplasm which contains only a small 

 amount of RNA-particles and endoplasmic 

 reticulum. These cell organelles are probably 

 used only for maintaining the restricted 

 amount of protein that is synthesized for 

 metabolic processes within the cell. The 

 number of cilia per cell is large; in the rat 

 trachea, it amounts to between 250 and 300. 

 The cilium is covered by the plasma mem- 

 brane and its interior represents an exten- 

 sion of the cytoplasm of the cell. Within 

 this cytoplasm is a number of distinct fibrils 

 oriented longitudinally. They originate from 

 the basal body which is located intracellu- 

 lar ly below the level of the cell surface. There 

 are two central single filaments and nine pe- 

 ripheral double ones. They all join in the tip 

 of the cilium. The central ones divide and 

 split within the basal body and wrap around 

 its central core. The peripheral filaments ex- 

 tend below the basal body and terminate at 

 various levels in the upper part of the ciliated 

 cell as ciliary rootlets. Beneath the basal 

 bodies are clusters of mitochondria, the 

 carriers of enzymes in all cells. It is believed 

 that the filaments of the cilium are contrac- 

 tile. The motion center is represented by the 

 basal body, and the energy recjuired for the 

 contraction is derived from the nearby 

 mitochondria. It has been demonstrated that 

 the ciliary beat can occur as long as the con- 

 tact between the basal body and the cilium 

 proper is maintained. Physical damage, 

 which involves a break between the cilium 

 and the basal body will, therefore, stop the 

 ciliary beat. However, it has also been 

 shown that toxic gases as well as cigarette 

 smoke at a certain concentration stop the 



Fig. 8. A schematic representation of the col- 

 umnar ciliated epithelium of the rat trachea. Con- 

 trary to that of man, this epithelium lacks an 

 evident layer of basal cells (BC) although some 

 may be seen in between the bases of the ciliated 

 (C) and the non-ciliated cells. Among the non-cili- 

 ated cells are found mucous cells (C) in various 

 states of mucous secretion, and brush cells (BRC). 

 The basement membrane is thinner in rat than in 

 man. (After Rhodin and Dalhamn, 1956). 



ciliary activity. Furthermore, infections like 

 influenza damage the ciliated cells so dras- 

 tically that eventually these cells die and 

 become sloughed off. They are then replaced 

 by basal cells which develop into brush cells 

 and from there into cihated cells (Figs. 3, 4, 

 5). 



REFERENCES 



Fawcett, D. W., and Porter, K. R., "A study of 



the fine structure of ciliated epithelia," /. 



Morph., 94, 221 (1954). 

 Rhodin, J. and Dalhamn, T., "Electron micros- 



copj- of the tracheal ciliated mucosa in rat," 



Z. Zellf., 44, 345 (1956). 

 Rhodin, J., "Ciliated epithelia," Int. Rev. CytoL, 



10 (1962). 



Johannes A. G. Rhodtn 



COLLOIDS, LYOPHOBIC 



The Colloidal State 



The colloidal state is essentially that state 

 in which matter exists with at least one 

 dimension in the size range 10~^ to 10~^ cm. 

 In this state can be included large molecules 



123 



