THE LUNGS. 



571 



fifty-two or even fifty-six and seventy-eight hours after death (Biermer, 

 Gosselin).* There is nothing to show the occurrence, normally, of a 

 desquamation of the ciliated epithelium of the larynx and air-passages. 



Fisr. 233. 



Occasionally, it is true, isolated, ciliated cylinders are thrown off and 

 expelled with the mucus of the trachea, but of an extensive detachment 

 of the ciliated cells there is no indication. Even in diseases of the re- 

 spiratory passages, the detachment of the ciliated cells is by no means 

 so common a phenomenon as is believed by many, and the epithelium 

 may be frequently found uninjured under puriform mucus, or even be- 

 neath croupose exudations. The mode in which the ciliated cylinders 

 that have been thrown off are replaced, is probably simply this : that 

 the deep cells multiply, perhaps by division (vide 12), and succeed 

 them, the outermost again producing cilia. 



The laryngeal mucous membrane contains a considerable number of 



FIG. 233. Ciliated epithelium from the human trachea, magnified 350 diam. Jl, epithelium 

 in situ : a, most external portion of the elastic longitudinal fibres ; 6, homogeneous, most ex- 

 ternal layer of the mucous membrane ; c, deepest, rounded cells ; d, middle, elongated cells ; 

 e, most superficial cells, supporting cilia. B, isolated cells from the various layers. 



* [The motion of the cilia is destroyed by many chemical and mechanical agents, but 

 hitherto, notwithstanding the careful researches of Purkinje and Valentin (De phenomeno. 

 gen. et fundam. motus vibratorii continui, Vratisl. 1835, pp. 74-7G) none have been known 

 which possessed the power of re-exciting it. Virchow (Archiv f. path. Anat. VI. 1) has, 

 however, quite lately, whilst examining the epithelium of a human trachea, discovered 

 that by the application of a solution of potassa the ciliary motion may be recalled. Under 

 the action of the potassa, he states, isolated cilia begin at first to exhibit irregular, jerking 

 movements. These gradually acquire more regularity and force, until at last the rapid, 

 rhythmical, sweeping movement of a whole series of cells is restored. A solution of soda 

 acts in the same manner as one of potassa ; a solution of ammonia produces, on the other 

 hand, at once a chemical decomposition. These experiments, Virchow thinks, prove con- 

 clusively, that the substance of the vibratile cilia approximates the contractile substance of 

 muscle (Syntonin of Lehmann). DaC.] 



