136 PRACTICAL HISTOLOGY. [vi. 



(&.) (H) Select a single, cilium observe that it is a clear homo- 

 geneous tapering filament, placed on a clear band which covers the 

 cells on the surface of the bar of the gill. Notice how the cilium 

 bends more at the top than base, and how it straightens itself again. 

 The movement may go on for several hours. The backward move- 

 ment is less rapid than the forward stroke. 



3. Heat (H). By means of a camel-hair brush run a ring of oil 



Fia. 96. Slide with a King of Glass Tube fixed to it, for Studying the Action of 

 Chloroform on Cilia. 



round the preparation (2), and put it aside for an hour or so, until 

 the ciliary motion becomes slower. 



(a.) Place the slide on a hot stage (fig. 75) and gradually apply 

 heat. As the cilia are warmed they move more quickly; but if the 

 temperature be too high, of course the proteids are coagulated and 

 the cells killed. If, while the cilia are moving rapidly, the source 

 of heat be removed, as the preparation cools the cilia gradually move 

 more and more slowly. 



Use the hot stage described in Lesson III. 5. But in using it, 

 put the preparation of cilia on a cover-glass moistened with a drop 

 of sea-water, and invert the cover-glass over the aperture in the hot 

 stage, so that the drop of fluid and cilia hang in the little circular 

 cavity. 



4. Weak Alkalies. To a preparation in which the cilia move 

 languidly, apply a drop of -J per cent, solution of caustic potash. 

 This immediately revives their action for a short time ; but as the 

 alkali penetrates into the cells, it ultimately kills them. 



5. Chloroform (L and H). Place a fragment of a mussel's gill in 

 a drop of salt water on a cover-glass. Put a small drop of chloroform 

 in a glass cell and place the cover-glass on the cell, with the drop of 

 fluid hanging into the latter, as shown in fig. 96. 



(a.) (H) Observe the movement of the cilia, and, as the chloroform 

 vapour diffuses into the drop of water and acts on the cilia, how 

 they move slower and slower. If the action of the chloroform be 

 pushed too far, their movement will be arrested. If the action of 

 the chloroform be not too prolonged, and the preparation removed 

 and freely exposed to the air, the cilia may begin to move again. 



6. Action of Gases on Ciliary Motion, e.g., Carbon Dioxide. 

 Carbonic acid is generated in the usual way in a flask containing 



