EPITHELIUM. 59 



This little piece is then to be mounted in a one-fourth per 

 cent, salt solution, or serum, and examined. Along the free 

 edge of the mucous membrane the cilia will be seen engaged in 

 active vibratile motion. The appearance presented by a broad 

 expanse of moving cilia has been aptly described as resembling 

 a field of grain which is being swept by the wind, though the 

 motion is often much more rapid than this comparison would 

 imply. It will be seen that various substances, such as blood 

 globules, are propelled in a definite direction. When the frog's 

 mouth is open, all solid particles that are lodged upon the 

 mucous membrane are carried quietly but inevitably toward 

 the gullet, and down toward the stomach. The power of the 

 ciliary movement may be estimated, in a measure, by placing 

 some light but adhering body upon the anterior portion of the 

 roof of the mouth, and then inverting the animal. The sub- 

 stance immediately begins to ascend against gravity, and soon 

 is wedged in the gullet. The same force, though acting in an 

 opposite direction, expels mucus, pus, and indeed all solid 

 matters, from the cavities of the human lungs ; it also propels 

 the ova through the Fallopian tubes into the uterus. In ex- 

 cessive catarrh from mucous membranes the epithelial bodies 

 may themselves be expelled, so that they are not infrequently 

 found with their cilia attached, as in the nasal discharges. After 

 death cilia are hard to recognize ; they contract down to little 

 knobs on the surface of the cells, and can only be demonstrated 

 when the eye looks directly down upon them. Osmic acid is 

 useful to preserve them in their natural condition. Take a fresh 

 specimen and immerse it for twenty-four hours in a one-fourth 

 percent, osmic acid solution, arid for another twenty -four hours 

 in dilute alcohol ; then tease and mount in glycerine and water. 

 It will be observed that each cilium is a slim, straight rod, which 

 is apparently structureless ; they rest upon a band, which, with 

 a high power, may be seen to have vertical striations. 



Effect of reagents. By making use of the moist chamber 

 (Fig. 19, p. 42), and placing a drop of chloroform in the cor- 

 ner of the cell, it will be seen that the action of the cilia rap- 

 idly stops, while, if the chloroform be removed, it will again 

 resume its activity. 



If carbonic acid gas is admitted, the action of the cilia will 

 at first be accelerated, but subsequently retarded, and eventu- 

 ally stopped (Kuehne). 



