146 



ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



fibrillae, of muscle ; and we must regard them as being, like those fibrillae, 

 organs sui generis, Saving their own peculiar endowment, which is, in the 

 higher animals at least, that of continuing in ceaseless vibration, during the 

 whole term of the life of the cells to which they are attached. 



[That this movement is truly molecular and independent of muscular influence and of 

 both the vascular and nervous systems has been proved by experiment. For, besides continu- 

 ing to manifest itself in a single particle for many hours after it has been isolated from 

 the rest of the system, a ciliated surface continues unaffected in its movements though the 

 supply of blood to the subjacent tissues be completely cut off. Neither do hydrocyanic 

 acid, opium, strychnine, belladonna, substances which affect powerfully the nervous sys- 

 tem, exert any influence on ciliary motion ; this phenomenon continuing in the bodies of 

 animals killed by these poisons. And lastly, shocks of electricity passed through the ciliated 

 parts, even the removal of the brain and spinal marrow in frogs, extinguishing as it does 

 muscular motion, do not destroy the action of cilia. 'M. C.] 



The length of time during which the Ciliary movement continues after the 

 general death of the body, is much less in the warm-blooded than in the cold- 

 blooded animals; and in this respect it corresponds with the degree of per- 

 sistence of muscular irritability, and of other vital endowments. 



173. A layer of Ciliated epithelium, of the Tesselated form, is found upon 

 the delicate pia mater which lines the cerebral cavities, not even excepting the 

 mfundibulum and the aqueduct of Sylvius ; and it is also found in the termi- 

 nal ramifications of the bronchial tubes. A Cylindrical epithelium furnished 

 with Cilia is found lining the nasal cavities, the frontal sinuses, the maxillary 

 antra, the lachrymal ducts and sac, the posterior surface of the velum pendu- 

 lum palati, and fauces, the Eustachian tube, the larynx, trachea, and bronchi 

 to their finest divisions, 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 secretions, which would otherwise accumu- 

 late on these membranes, towards the exterior orifices, whence they may be 

 carried off. 



174. The Epithelium-cells, like the scales of the Epidermis, are continually 

 being cast off and renewed from the subjacent surface; but the rapidity of 

 this renewing process varies according to the particular function of the part. 

 Thus we shall hereafter find it to be greater on the Mucous Membranes, 

 which are actively engaged in the introduction of nutrient materials and in the 

 separation of effete matter, than it is on the Serous surfaces, which are com- 

 paratively inert. The epithelial cells that cover the plane surfaces, seem to 

 be developed from granular germs, scattered through the subjacent basement 

 membrane ; but it is different in regard to the cells of the glandular follicles, 

 which usually seem to originate in a single " germinal spot," composed of a 

 mass of granules, at the blind extremity of the follicles. In fact, each of these 

 follicles may be regarded as a parent-cell, which was closed at an earlier 

 period of its existence, and which, even after it has ruptured and given exit 

 to its contents, goes on forming a succession of new generations from its 



nucleus. The accompanying figure represents 

 two follicles of the liver of the common Crab, 

 which are seen to be filled witli secreting cells ; 

 and it is evident, from a comparison of the sizes 

 of the cells at different parts, that they originate 

 at the blind extremity of the follicle, where there 

 is a germinal spot ; and that, as they recede 

 from that point and approach the outlet of the 

 follicle, they gradually increase in size and be- 

 come filled with their characteristic secretion ; be- 

 ing at the same time pushed onwards towards 



Fig. 41. 



Two follicles from the liver of Car- 

 einns mrenas (Common Crnli), with 

 their contained secreting cells. 



