PHENOMENA IN THE ANIMAL BODY. 361 



is by much the most extraordinary in the whole 

 animal economy.* A portion of the mucous mem- 

 brane of an animal recently killed is placed, with 

 great nicety, under the field of the microscope, 

 and in water: some fine particles, which will float 

 in the water, are then added. What has been 

 used with most advantage is the black pigment of 

 the eye, which is easily diflfused, and the particles 

 of which are very minute. The experimenter is 

 here cautioned to distinguish the molecular mo- 

 tions discovered by Mr. Brown, from those now 

 to be described. A rapid vibratory motion is to 

 be seen on the surface of the membrane, and 

 these motions produce a current in the fluid in 

 contact, which is made apparent by the floating 

 of the minute particles of the pigment. The re- 

 markable part of this phenomenon is the direction 

 of these currents. The cilia, or small filaments 

 projecting from the membrane, move in such a 

 manner that the current is always directed to- 

 wards the outlet of the cavity or tube ; and thus 

 it is conjectured that a new source and kind of 

 action, independent of muscularity, (that is, the 

 irritability of the grosser muscular fibre,) is pro- 

 vided for the gradual and regular ejection of the 

 secretions from these tubes and cavities which 

 enter deep into the animal structure. In this 

 country these extraordinary endowments of the 



* First observed by Purkinjo and Valentin. 

 32 



