158 MANUAL OF HISTOLOGY. 



warmth of the body, and thus transforms their contents into nnicin 

 (Simon, Frerichs). If this mode of explaining its origin be correct, mucin 

 must represent in numerous cases a physiological transformation product 

 of epithelial tissue. 



97. 



To what extent epithelial cells are endowed with the property of vital 

 contractility, when young and still soft, we are for the present unable to 

 state. But a most remarkable movement is met with on the other hand 

 in ciliated epithelia, which has been named ciliary motion (Motus vibra- 

 to ius). This phenomenon, known from the earliest epochs of microscopic 

 research, has been recently very closely studied, but unfortunately with 

 but small results. For although its wide distribution throughout the 

 animal kingdom has been recognised, and ciliary motion not long since 

 observed in low vegetable organisms, we are still completely in the dark 

 as to its mechanism and object. The elucidation of points of this kind 

 regarding it are rendered thus difficult by the fact, that the phenomenon 

 of ciliary motion is met with in very varied extent throughout the animal 

 kingdom, parts which are ciliated in one class being no longer so in, 

 another group ; thus, for instance, none of these cells can be found among 

 any of the arthropoda. 



Ciliary motion, a simultaneous and regular swinging of all the minute 

 hairs, appears, as seen on the edge of a fold of membrane, somewhat 

 like to the undulation of a shaken cloth, or the flickering of a candle 

 flame. Seen from above it frequently reminds us of the waving of a 

 tield of corn moved by the wind, or when it takes place in a tube of 

 extreme fineness, of the current of a brook in the sun light. All these 

 comparisons, however, are perhaps hardly adequate to express the pecu- 

 liarity of the appearance. 



Small particles suspended in water as, for instance, blood-corpuscles 

 and pigmentary granules are driven along by the movements of the cilia 

 at the edge of a membrane possessing them in one definite direction, and 

 apparently with great rapidity when the action is energetic, and the 

 magnifying power great. In reality, however, this rapidity is much less 

 than it seems, but still by no means inconsiderable, for an interval of an 

 inch may be traversed by one of these particles in a few minutes. Even 

 a shred of a ciliated stratum of cells may be driven along by the motion of 

 its own particular cilia, if it be not altogether too large, while a smaller 

 piece, or single detached cell, may whirl itself through the water in 

 a lively manner, simulating in a most deceptive way the motions of the 

 infusoria. 



However, in a fresh state, and when the cilia are endued with great 

 vital energy, the motions of the hairs follow so rapidly in succession, that 

 the latter are not seen, nor can the phenomenon be recognised as a rule. 

 Several vibrations are usually observed to take place in the course of a 

 single second. 



For the closer examination of the phenomenon that moment is most 

 suitable at which the movement of the cilia has become slower and 

 weaker, owing to the approaching death of the cells, and when each 

 individual little hair may be observed for itself. The mode in which it 

 is carried out is not always the same, so that the motion has been classified 

 into four varieties (Purkinje and Valentin), namely, into (1), the hook- 

 like (hakenformige), in which each cilium makes the movement of a 



