. Principles of human physiology : with their chief applications to pathology, hygiene, and forensic medicine : especially designed for the use of students. urfaces, which are, in their natural and healthy state, lubricatedby fluid, are covered with a multitude of hair-like processes, of extremedelicacy of structure and minuteness of size. These are called cilia, fromcilium, an eye-lash. They are generally conical in shape, being attachedby their bases to the epithelium that covers the surface on which they play,and tapering gradually to a point; or, as Purkinje and Valentin state, theyare mor
. Principles of human physiology : with their chief applications to pathology, hygiene, and forensic medicine : especially designed for the use of students. urfaces, which are, in their natural and healthy state, lubricatedby fluid, are covered with a multitude of hair-like processes, of extremedelicacy of structure and minuteness of size. These are called cilia, fromcilium, an eye-lash. They are generally conical in shape, being attachedby their bases to the epithelium that covers the surface on which they play,and tapering gradually to a point; or, as Purkinje and Valentin state, theyare more or less flattened processes, of which the free extremities arerounded; and this latter form prevails in the human subject. They varyin length from the ToW to the j^^q- of an inch. They are disposed inrows, and are adapted in their arrangement to the shape and extent of thesurface to which they belong; they adhere to the edges, or to a portion ofthe surface, of the particles of the epithelium, preferring the columnarvariety of them. During life, and for a certain period after death, these filaments exhibit aremarkable movement, of a fan- Fig. 55, ning or a lashing kind, so thateach cilium bends rapidly in onedirection, and returns again tothe quiescent state. The mo-tion, when viewed under a highmagnifying power, is singularlybeautiful, presenting an appear-ance somewhat resembling thatof a field of corn agitated by asteady breeze. Any minute ob-jects coming in contact with thefree extremities of the cilia arehurried rapidly along in the di-rection of the predominant move-ment; one or more blood-discs,accidentally present, will some-times pass rapidly across thefield, propelled in this way, andvery minute particles of pow-dered charcoal may be conveni-ently used to exhibit this phe-nomenon, and to indicate the di-rection of the movement. The action of the cilia produces a current inthe surrounding fluid, the direction of which is shown by the course whichthe propelled part
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Keywords: ., bookcentury1800, bookdecade1840, bookpubli, booksubjectphysiology
