36 EPITHELIUM AND ENDOTHELIUM. 



is either exceedingly languid or has ceased altogether, and 



cautiously allow a small quantity of a very delicate solution. 



of potash to act upon it by the irrigation process, we soon ob- 

 serve that the motion is renewed ; becoming equal in rapidity 

 to that seen in the perfectly fresh preparation. The restora- 

 tion of motion is not due to any special property of potash ; 

 nor can it be attributed to the influence of that reagent in dis- 

 solving coagulated material between the cilia, which might be 

 supposed to interfere median \ca\\y with their movements. 

 This is proved by the fact that many other reagents act simi- 

 larly as stimulants of ciliary motion e. </., distilled water, half 

 per cent, solution of common salt, dilute acetic acid, carbonic 

 acid, or the induced current (applied according to the method 

 described in Chapter I.). All these, if used with great care, 

 accelerate the movement in the first instance. The accele- 

 ration lasts only for a short time, and, in most cases, is quick- 

 ly followed by cessation of movement, consequent upon the 

 destructive influence of the reagent used. After the addition 

 of dilute acetic acid (and still more rapidly with concentrated) 

 the bodies of the cells swell and become transparent, and their 

 nuclei well defined, in the same manner as after the addition 

 of water. The investigation of the respective actions of carbo- 

 nic acid gas and oxygen upon ciliary movement is a very im- 

 portant experiment. We make a preparation of the ciliated 

 epithelium from the throat of the frog, in a half per cent, solu- 

 tion of common salt upon a cover-glass, which is then placed 

 on a ring of putty over the gas-chamber of the movable stage 

 (Fig. 2). Into this chamber a drop of water has been previous- 

 ly placed to keep it moist, and if we now allow a stream of 

 carbonic acid to pass, we perceive, as has been already men- 

 tioned, that for a few moments the ciliary motion becomes 

 quicker, but, by-and-by, slower, until it finally ceases. On 

 now substituting atmospheric air (oxygen), we find that the 

 movement slowly recommences, and, before long, is quite as 

 active as before the passage of the carbonic acid. The experi- 

 ment m&y be repeated several times with a like result, until at 

 last the motion can no longer be excited. Oxygen is there-, 

 fore as essential for the continuance of motion in the indi- 

 vidual ^ciliated cell as for the maintenance of animal life in 

 general. 



Study of Ciliary Motion in Situ. To demonstrate 

 ciliary action on a membrane in situ, the most judicious plan 

 is to remove from a female frog or toad that portion of peri- 

 toneum which covers the cisterna lymphalica magna, the so- 

 called septum of the cisterna. Or, instead of this, a portion 

 of the parietal peritoneum of the anterior abdominal wall of 

 the newt may be employed. In either case, the part removed 

 is to be quickly and carefully spread -upon a glass slide with 



