472 



OF NUTRITION. 



Fig. 101 



[Certain surfaces, which are, in their natural and healthy state, lubricated by fluid, are 

 covered with a multitude of hair-like processes, of extreme delicacy of structure and 

 minuteness of size. These are called cilia, from ciliurn, an eyelash. They are generally 

 conical in shape, being attached by 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, 

 they are more or less flattened processes, of which the free extremities are rounded ; and 

 this latter form prevails in the human subject. They vary in length from the 1-lOOOth to 

 the l-12,000th of an inch. They are disposed in rows, and are adapted in their arrange- 

 ment to the shape and extent of the surface to which they belong; they adhere to the 

 edges, or to a portion of the surface, of the particles of the epithelium, preferring the 

 columnar variety of them. 



During life, and for a certain period after death, these filaments exhibit a remarkable 



movement, of a fanning or a lashing 

 kind, so that each cilium bends rapidly 

 in one direction, and returns again to 

 the quiescent state. The motion, when 

 viewed under a high magnifying power, 

 is singularly beautiful, presenting an 

 appearance somewhat resembling that 

 of a field of corn agitated by a steady 

 breeze. Any minute objects coming in 

 contact with the free extremities of the 

 cilia are hurried rapidly along in the 

 direction of the predominant movement; 

 one or more blood discs, accidentally 

 present, will sometimes pass rapidly 

 across the field, propelled in this way, 

 and very minute particles of powdered 

 charcoal may be conveniently used to 

 exhibit this phenomenon, and to indicate 

 the direction of the movement. The 

 action of the cilia produces a current in 



Examples of Cilia; 1, portion of a bar of the gill of 

 the sea-mussel, Mytilus edulis, showing cilia attest and 

 in motion ; 2, ciliated epithelium particles from the frog's 

 mouth ; 3, ciliated epithelium particles from inner sur- 

 face of human membrana tympani; 4, ditto, ditto, from 

 the human bronchial mucous membrana; 5, Leucophrys 

 patula, a polygastric infusory animalcule ; to show its 

 surface covered with cilia, and the mouth surrounded 

 by them. 



the surrounding fluid, the direction of 

 which is shown by the course which the 

 propelled particles take. 



An easy way to observe this pheno- 

 menon is to detach by scraping with a 

 knife a few scales of epithelium from 

 the back of the throat of a living frog. 

 These, moistened with water or serum, 

 will continue to exhibit the movement 



of their adherent cilia for a very considerable time, provided the piece be kept duly 

 moistened. On one occasion we observed a piece prepared in this way exhibit motion 

 for seventeen hours; and it would probably have continued doing so for a longer time, 

 had not the moisture around it evaporated. However, Purkinje and Valentin have 

 observed it to last for a much longer time than this in connection with the body of the 

 animal. In the turtle, after death by decapitation, they found it lasted, in the mouth, nine 

 days; in the trachea and the lungs, thirteen days; and, in the oesophagus, nineteen days. 

 In frogs, from which the brain had been removed, it lasted from four to five days. The 

 longest time they observed it to continue in man and mammalia was two days; but in 

 general it did not last nearly so long. What appears to be immediately necessary to the 

 continuation of the movement, is the integrity of the epithelial cells to which the cilia 

 adhere ; for as soon as these shrink up for want of moisture, or become physically altered 

 by chemical reagents or by the progress of putrefaction, the cilia immediately cease to 

 play. 



From these facts we learn two important points in connection with this phenomenon. 

 The first is, the truly molecular character of the movement. Whatever be the immediate 

 cause of the action of the cilia, it is evidently intimately connected with the minute 

 epithelial particles to which they are attached ; for cilia never exist in man and the 

 higher animals without epithelial particles, and these particles have no organic connec- 

 tion with the subjacent textures, excepting such as may arise from simple adhesion. 

 And, secondly, we perceive, that this movement is independent of both the vascular and 

 the nervous systems, for it will continue to manifest itself for many hours in a single 

 particle isolated from the rest of the system. After death it remains longer than the con- 

 tractility of muscle; a circumstance which, together with the facts just mentioned, indi- 

 cates that the cilia cannot be moved by little muscles inserted into their bases, as some 



