38 



consequence of the imperfections of the old microscope. 

 These were the motions of minute hairs, or cilia, which 

 existed upon the surface of serous, mucous, and other 

 memhranes. These cilia were inconceivably small, 

 varying in length from the t^oo to tm of an inch; in 

 thickness from about smm to gojbo of an inch ; they were 

 attached usually to epithelial cells or scales, and from this 

 circumstance it was impossible to suppose that they were 

 passive agents, moved by smaller muscles. Each cilium 

 had a variety of movements, lashing backwards and for- 

 wards, from side to side, or in continuous rotatory motion. 

 Fluid was absolutely necessary for them to perform their 

 functions, which were evidently to produce currents in the 

 liquid, so that a fresh supply might be constantly arriving 

 at that part of the surface to which they were attached. 

 The gills of fish and crustaceans were covered with them. 

 The most extraordinary phenomenon connected with their 

 motions, was their long continuance after the death of 

 the animal in which they existed. Under favourable 

 circumstances, the cilia from the turtle had been found in 

 active operation sixteen days after death. Chemical re- 

 agents affected them variously ; acids and alkalies, when 

 weak, produced quiescence, galvanism and opium had no 

 effect; blood made them move faster, but bile destroyed 

 their motions at once. 



But these organs, though they were not under any 

 vital influence in the higher animals, became the voluntary 

 organs of locomotion in many of the infusoria. Many 

 of these were found to have their bodies covered with 

 cilia, which were in action, or at rest, according to the 

 exigencies of the animalcule : others were furnished with 

 cilia around the mouth only, which acted as organs of 

 prehension, and were moved in any direction at will. 

 These cilia, though they were similar in appearance to 

 those in the higher classes, differed from them materially. 



