CILIARY MOVEMENT. 237 



from the body. Thus isolated epithelium-cells have been seen to swim about 

 actively in water, by the agency of their cilia, for some hours after they have 

 been detached from the mucous surface of the nose ; the ciliary movement has 

 been seen fifteen days after death in the body of a Tortoise, in which putrefaction 

 was far advanced; and even in Man, according to the recent observations of M. 

 Gosselin, 1 it may be observed on the mucous lining of the trachea for as long as 

 seven days after death. The purpose of this Ciliary movement is obviously to 

 propel fluids over the surface on which it takes place ; and it is consequently 

 limited, in all save aquatic animals, to certain internal surfaces of the body, and 

 takes place in the direction of the outlets, towards which it aids in propelling the 

 various products of secretion. A layer of ciliated epithelium, of the tessellated 

 form, has been affirmed by Purkinje and Valentin to exist upon the delicate pia 

 mater which lines the cerebral cavities, not even excepting the infundibulum and 

 the aqueduct of Sylvius ; but from the recent observations of Dittrich and Gerlach 

 upon decapitated criminals, it is doubtful if this movement takes place in the 

 Human adult, the previously-cited results having been afforded by embryos and 

 by the lower animals. 2 A cylindrical epithelium furnished with cilia is found 

 lining the nasal cavities, except over the olfactory region, the frontal sinuses, 

 the maxillary antra, the lachrymal ducts and sac, the posterior surface of the 

 velum pendulum palati, and fauces, the Eustachian tube, the larynx, trachea, and 

 bronchi to their finest divisions, where it passes into the tessellated form, the 

 upper portion of the vagina, the uterus, and the Fallopian tubes. The function 

 of the cilia in all these cases appears to be the same ; that of propelling the se- 

 cretions, which would otherwise accumulate on these membranes, towards the 

 exterior orifices, whence they may be carried off. 



232. Of the agency to which the Ciliary movement is immediately due, it is 

 difficult to give any precise account. Although the fact cannot be substantiated 

 in the case of the minute cilia of the epithelium-cells of Man, yet a careful 

 examination of the much larger cilia of some of the lower animals, especially 

 aquatic Mollusks and Animalcules, suggests the idea that they are veritable pro- 

 longations of the cells, of which they have usually been regarded as mere appur- 

 tenances; 3 and that their rhythmical movement is to be regarded, no less than 

 the changes of shape in entire cells, as a manifestation of cell-force (110). It 

 certainly depends upon the continued vitality of the cell, and is affected by 

 agencies which tend to increase or to repress its vigor. And the fact already 

 mentioned ( 113) as to the reciprocity of ciliary movement and secretory 

 action, is a strong indication that both proceed from the same dynamical source. 

 It has been maintained by some, that the action of the cilia is muscular ; but 

 these filaments are usually too small to contain even the minutest fibrillse of 

 true muscular tissue ; and we can scarcely but regard them as organs sui generis, 

 which do not owe their peculiar endowments to any other. 



233. The Epithelium of most parts of the surface of the Mucous Membranes 

 appears to be frequently exuviated and renewed; in fact, in most cases in 

 which it has a true secretory action, that action is completed by the detach- 

 ment of the epithelial cells, after they have developed themselves at the expense 

 of the peculiar matter which they have drawn from the blood ; and preparation 

 is soon made by a new growth for a repetition of the secreting process. No 



1 "Gazette Medicale," 1851, No. 26. These observations were made at the Ecole Prat- 

 ique, on the body of a decapitated criminal. 



2 See the "Priiger Vierteljahrschrift" for 1851, cited in the "Edinb. Monthly Journ. ," 

 Jan. 1852, p. 82. 



3 This is certainly the case with regard to the long filamentous processes of many (so- 

 called) Animalcules, which only differ from cilia in being of much larger size, and in not 

 being multiple ; between the two forms, however, there are many intermediate gradations, 

 so that the similarity of their nature can scarcely be doubted. 



